/* Alias analysis for trees. Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. Contributed by Diego Novillo This file is part of GCC. GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GCC; see the file COPYING3. If not see . */ #include "config.h" #include "system.h" #include "coretypes.h" #include "tm.h" #include "tree.h" #include "rtl.h" #include "tm_p.h" #include "hard-reg-set.h" #include "basic-block.h" #include "timevar.h" #include "expr.h" #include "ggc.h" #include "langhooks.h" #include "flags.h" #include "function.h" #include "diagnostic.h" #include "tree-dump.h" #include "gimple.h" #include "tree-flow.h" #include "tree-inline.h" #include "tree-pass.h" #include "tree-ssa-structalias.h" #include "convert.h" #include "params.h" #include "ipa-type-escape.h" #include "vec.h" #include "bitmap.h" #include "vecprim.h" #include "pointer-set.h" #include "alloc-pool.h" /* Broad overview of how aliasing works: First we compute points-to sets, which is done in tree-ssa-structalias.c During points-to set constraint finding, a bunch of little bits of information is collected. This is not done because it is necessary for points-to, but because points-to has to walk every statement anyway. The function performing this collecting is update_alias_info. Bits update_alias_info collects include: 1. Directly escaping variables and variables whose value escapes (using is_escape_site). This is the set of variables and values that escape prior to transitive closure of the clobbers. 2. The set of variables dereferenced on the LHS (into dereferenced_ptr_stores) 3. The set of variables dereferenced on the RHS (into dereferenced_ptr_loads) 4. The set of all pointers we saw. 5. The number of loads and stores for each variable 6. The number of statements touching memory 7. The set of address taken variables. #1 is computed by a combination of is_escape_site, and counting the number of uses/deref operators. This function properly accounts for situations like &ptr->field, which is *not* a dereference. After points-to sets are computed, the sets themselves still contain points-to specific variables, such as a variable that says the pointer points to anything, a variable that says the pointer points to readonly memory, etc. These are eliminated in a later phase, as we will see. The rest of the phases are located in tree-ssa-alias.c The next phase after points-to set computation is called "setup_pointers_and_addressables" This pass does 3 main things: 1. All variables that can have TREE_ADDRESSABLE removed safely (IE non-globals whose address is not taken), have TREE_ADDRESSABLE removed. 2. All variables that may be aliased (which is the set of addressable variables and globals) at all, are marked for renaming, and have symbol memory tags created for them. 3. All variables which are stored into have their SMT's added to written vars. After this function is run, all variables that will ever have an SMT, have one, though its aliases are not filled in. The next phase is to compute flow-insensitive aliasing, which in our case, is a misnomer. it is really computing aliasing that requires no transitive closure to be correct. In particular, it uses stack vs non-stack, TBAA, etc, to determine whether two symbols could *ever* alias . This phase works by going through all the pointers we collected during update_alias_info, and for every addressable variable in the program, seeing if they alias. If so, the addressable variable is added to the symbol memory tag for the pointer. As part of this, we handle symbol memory tags that conflict but have no aliases in common, by forcing them to have a symbol in common (through unioning alias sets or adding one as an alias of the other), or by adding one as an alias of another. The case of conflicts with no aliases in common occurs mainly due to aliasing we cannot see. In particular, it generally means we have a load through a pointer whose value came from outside the function. Without an addressable symbol to point to, they would get the wrong answer. After flow insensitive aliasing is computed, we compute name tags (called compute_flow_sensitive_info). We walk each pointer we collected and see if it has a usable points-to set. If so, we generate a name tag using that pointer, and make an alias bitmap for it. Name tags are shared between all things with the same alias bitmap. The alias bitmap will be translated from what points-to computed. In particular, the "anything" variable in points-to will be transformed into a pruned set of SMT's and their aliases that compute_flow_insensitive_aliasing computed. Note that since 4.3, every pointer that points-to computed a solution for will get a name tag (whereas before 4.3, only those whose set did *not* include the anything variable would). At the point where name tags are all assigned, symbol memory tags are dead, and could be deleted, *except* on global variables. Global variables still use symbol memory tags as of right now. After name tags are computed, the set of clobbered variables is transitively closed. In particular, we compute the set of clobbered variables based on the initial set of clobbers, plus the aliases of pointers which either escape, or have their value escape. After this, maybe_create_global_var is run, which handles a corner case where we have no call clobbered variables, but have pure and non-pure functions. Staring at this function, I now remember it is a hack for the fact that we do not mark all globals in the program as call clobbered for a function unless they are actually used in that function. Instead, we only mark the set that is actually clobbered. As a result, you can end up with situations where you have no call clobbered vars set. After maybe_create_global_var, we set pointers with the REF_ALL flag to have alias sets that include all clobbered memory tags and variables. After this, memory partitioning is computed (by the function compute_memory_partitions) and alias sets are reworked accordingly. Lastly, we delete partitions with no symbols, and clean up after ourselves. */ /* Alias information used by compute_may_aliases and its helpers. */ struct alias_info { /* SSA names visited while collecting points-to information. If bit I is set, it means that SSA variable with version I has already been visited. */ sbitmap ssa_names_visited; /* Array of SSA_NAME pointers processed by the points-to collector. */ VEC(tree,heap) *processed_ptrs; /* ADDRESSABLE_VARS contains all the global variables and locals that have had their address taken. */ struct alias_map_d **addressable_vars; size_t num_addressable_vars; /* POINTERS contains all the _DECL pointers with unique memory tags that have been referenced in the program. */ struct alias_map_d **pointers; size_t num_pointers; /* Pointers that have been used in an indirect load/store operation. */ struct pointer_set_t *dereferenced_ptrs; }; /* Structure to map a variable to its alias set. */ struct alias_map_d { /* Variable and its alias set. */ tree var; alias_set_type set; }; /* Counters used to display statistics on alias analysis. */ struct alias_stats_d { unsigned int alias_queries; unsigned int alias_mayalias; unsigned int alias_noalias; unsigned int simple_queries; unsigned int simple_resolved; unsigned int tbaa_queries; unsigned int tbaa_resolved; unsigned int structnoaddress_queries; unsigned int structnoaddress_resolved; }; /* Local variables. */ static struct alias_stats_d alias_stats; static bitmap_obstack alias_bitmap_obstack; /* Local functions. */ static void compute_flow_insensitive_aliasing (struct alias_info *); static void dump_alias_stats (FILE *); static tree create_memory_tag (tree type, bool is_type_tag); static tree get_smt_for (tree, struct alias_info *); static tree get_nmt_for (tree); static void add_may_alias (tree, tree); static struct alias_info *init_alias_info (void); static void delete_alias_info (struct alias_info *); static void compute_flow_sensitive_aliasing (struct alias_info *); static void setup_pointers_and_addressables (struct alias_info *); static void update_alias_info (struct alias_info *); static void create_global_var (void); static void maybe_create_global_var (void); static void set_pt_anything (tree); void debug_mp_info (VEC(mem_sym_stats_t,heap) *); static alloc_pool mem_sym_stats_pool; /* Return memory reference stats for symbol VAR. Create a new slot in cfun->gimple_df->mem_sym_stats if needed. */ static struct mem_sym_stats_d * get_mem_sym_stats_for (tree var) { void **slot; struct mem_sym_stats_d *stats; struct pointer_map_t *map = gimple_mem_ref_stats (cfun)->mem_sym_stats; gcc_assert (map); slot = pointer_map_insert (map, var); if (*slot == NULL) { stats = (struct mem_sym_stats_d *) pool_alloc (mem_sym_stats_pool); memset (stats, 0, sizeof (*stats)); stats->var = var; *slot = (void *) stats; } else stats = (struct mem_sym_stats_d *) *slot; return stats; } /* Return memory reference statistics for variable VAR in function FN. This is computed by alias analysis, but it is not kept incrementally up-to-date. So, these stats are only accurate if pass_may_alias has been run recently. If no alias information exists, this function returns NULL. */ static mem_sym_stats_t mem_sym_stats (struct function *fn, tree var) { void **slot; struct pointer_map_t *stats_map = gimple_mem_ref_stats (fn)->mem_sym_stats; if (stats_map == NULL) return NULL; slot = pointer_map_contains (stats_map, var); if (slot == NULL) return NULL; return (mem_sym_stats_t) *slot; } /* Set MPT to be the memory partition associated with symbol SYM. */ static inline void set_memory_partition (tree sym, tree mpt) { #if defined ENABLE_CHECKING if (mpt) gcc_assert (TREE_CODE (mpt) == MEMORY_PARTITION_TAG && !is_gimple_reg (sym)); #endif var_ann (sym)->mpt = mpt; if (mpt) { if (MPT_SYMBOLS (mpt) == NULL) MPT_SYMBOLS (mpt) = BITMAP_ALLOC (&alias_bitmap_obstack); bitmap_set_bit (MPT_SYMBOLS (mpt), DECL_UID (sym)); /* MPT inherits the call-clobbering attributes from SYM. */ if (is_call_clobbered (sym)) { MTAG_GLOBAL (mpt) = 1; mark_call_clobbered (mpt, ESCAPE_IS_GLOBAL); } } } /* Mark variable VAR as being non-addressable. */ static void mark_non_addressable (tree var) { tree mpt; if (!TREE_ADDRESSABLE (var)) return; mpt = memory_partition (var); clear_call_clobbered (var); TREE_ADDRESSABLE (var) = 0; if (mpt) { /* Note that it's possible for a symbol to have an associated MPT and the MPT have a NULL empty set. During init_alias_info, all MPTs get their sets cleared out, but the symbols still point to the old MPTs that used to hold them. This is done so that compute_memory_partitions can now which symbols are losing or changing partitions and mark them for renaming. */ if (MPT_SYMBOLS (mpt)) bitmap_clear_bit (MPT_SYMBOLS (mpt), DECL_UID (var)); set_memory_partition (var, NULL_TREE); } } /* qsort comparison function to sort type/name tags by DECL_UID. */ static int sort_tags_by_id (const void *pa, const void *pb) { const_tree const a = *(const_tree const *)pa; const_tree const b = *(const_tree const *)pb; return DECL_UID (a) - DECL_UID (b); } /* Initialize WORKLIST to contain those memory tags that are marked call clobbered. Initialized WORKLIST2 to contain the reasons these memory tags escaped. */ static void init_transitive_clobber_worklist (VEC (tree, heap) **worklist, VEC (int, heap) **worklist2, bitmap on_worklist) { referenced_var_iterator rvi; tree curr; FOR_EACH_REFERENCED_VAR (curr, rvi) { if (MTAG_P (curr) && is_call_clobbered (curr)) { VEC_safe_push (tree, heap, *worklist, curr); VEC_safe_push (int, heap, *worklist2, var_ann (curr)->escape_mask); bitmap_set_bit (on_worklist, DECL_UID (curr)); } } } /* Add ALIAS to WORKLIST (and the reason for escaping REASON to WORKLIST2) if ALIAS is not already marked call clobbered, and is a memory tag. */ static void add_to_worklist (tree alias, VEC (tree, heap) **worklist, VEC (int, heap) **worklist2, int reason, bitmap on_worklist) { if (MTAG_P (alias) && !is_call_clobbered (alias) && !bitmap_bit_p (on_worklist, DECL_UID (alias))) { VEC_safe_push (tree, heap, *worklist, alias); VEC_safe_push (int, heap, *worklist2, reason); bitmap_set_bit (on_worklist, DECL_UID (alias)); } } /* Mark aliases of TAG as call clobbered, and place any tags on the alias list that were not already call clobbered on WORKLIST. */ static void mark_aliases_call_clobbered (tree tag, VEC (tree, heap) **worklist, VEC (int, heap) **worklist2, bitmap on_worklist) { bitmap aliases; bitmap_iterator bi; unsigned int i; tree entry; var_ann_t ta = var_ann (tag); if (!MTAG_P (tag)) return; aliases = may_aliases (tag); if (!aliases) return; EXECUTE_IF_SET_IN_BITMAP (aliases, 0, i, bi) { entry = referenced_var (i); /* If you clobber one part of a structure, you clobber the entire thing. While this does not make the world a particularly nice place, it is necessary in order to allow C/C++ tricks that involve pointer arithmetic to work. */ if (!unmodifiable_var_p (entry)) { add_to_worklist (entry, worklist, worklist2, ta->escape_mask, on_worklist); mark_call_clobbered (entry, ta->escape_mask); } } } /* Tags containing global vars need to be marked as global. Tags containing call clobbered vars need to be marked as call clobbered. */ static void compute_tag_properties (void) { referenced_var_iterator rvi; tree tag; bool changed = true; VEC (tree, heap) *taglist = NULL; FOR_EACH_REFERENCED_VAR (tag, rvi) { if (!MTAG_P (tag)) continue; VEC_safe_push (tree, heap, taglist, tag); } /* We sort the taglist by DECL_UID, for two reasons. 1. To get a sequential ordering to make the bitmap accesses faster. 2. Because of the way we compute aliases, it's more likely that an earlier tag is included in a later tag, and this will reduce the number of iterations. If we had a real tag graph, we would just topo-order it and be done with it. */ qsort (VEC_address (tree, taglist), VEC_length (tree, taglist), sizeof (tree), sort_tags_by_id); /* Go through each tag not marked as global, and if it aliases global vars, mark it global. If the tag contains call clobbered vars, mark it call clobbered. This loop iterates because tags may appear in the may-aliases list of other tags when we group. */ while (changed) { unsigned int k; changed = false; for (k = 0; VEC_iterate (tree, taglist, k, tag); k++) { bitmap ma; bitmap_iterator bi; unsigned int i; tree entry; bool tagcc = is_call_clobbered (tag); bool tagglobal = MTAG_GLOBAL (tag); if (tagcc && tagglobal) continue; ma = may_aliases (tag); if (!ma) continue; EXECUTE_IF_SET_IN_BITMAP (ma, 0, i, bi) { entry = referenced_var (i); /* Call clobbered entries cause the tag to be marked call clobbered. */ if (!tagcc && is_call_clobbered (entry)) { mark_call_clobbered (tag, var_ann (entry)->escape_mask); tagcc = true; changed = true; } /* Global vars cause the tag to be marked global. */ if (!tagglobal && is_global_var (entry)) { MTAG_GLOBAL (tag) = true; changed = true; tagglobal = true; } /* Early exit once both global and cc are set, since the loop can't do any more than that. */ if (tagcc && tagglobal) break; } } } VEC_free (tree, heap, taglist); } /* Set up the initial variable clobbers, call-uses and globalness. When this function completes, only tags whose aliases need to be clobbered will be set clobbered. Tags clobbered because they contain call clobbered vars are handled in compute_tag_properties. */ static void set_initial_properties (struct alias_info *ai) { unsigned int i; referenced_var_iterator rvi; tree var; tree ptr; bool any_pt_anything = false; enum escape_type pt_anything_mask = 0; FOR_EACH_REFERENCED_VAR (var, rvi) { if (is_global_var (var)) { if (!unmodifiable_var_p (var)) mark_call_clobbered (var, ESCAPE_IS_GLOBAL); } else if (TREE_CODE (var) == PARM_DECL && gimple_default_def (cfun, var) && POINTER_TYPE_P (TREE_TYPE (var))) { tree def = gimple_default_def (cfun, var); get_ptr_info (def)->value_escapes_p = 1; get_ptr_info (def)->escape_mask |= ESCAPE_IS_PARM; } } if (!clobber_what_escaped ()) { any_pt_anything = true; pt_anything_mask |= ESCAPE_TO_CALL; } compute_call_used_vars (); for (i = 0; VEC_iterate (tree, ai->processed_ptrs, i, ptr); i++) { struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr); tree tag = symbol_mem_tag (SSA_NAME_VAR (ptr)); /* A pointer that only escapes via a function return does not add to the call clobber or call used solution. To exclude ESCAPE_TO_PURE_CONST we would need to track call used variables separately or compute those properly in the operand scanner. */ if (pi->value_escapes_p && pi->escape_mask & ~ESCAPE_TO_RETURN) { /* If PTR escapes then its associated memory tags and pointed-to variables are call-clobbered. */ if (pi->name_mem_tag) mark_call_clobbered (pi->name_mem_tag, pi->escape_mask); if (tag) mark_call_clobbered (tag, pi->escape_mask); } /* If the name tag is call clobbered, so is the symbol tag associated with the base VAR_DECL. */ if (pi->name_mem_tag && tag && is_call_clobbered (pi->name_mem_tag)) mark_call_clobbered (tag, pi->escape_mask); /* Name tags and symbol tags that we don't know where they point to, might point to global memory, and thus, are clobbered. FIXME: This is not quite right. They should only be clobbered if value_escapes_p is true, regardless of whether they point to global memory or not. So removing this code and fixing all the bugs would be nice. It is the cause of a bunch of clobbering. */ if ((pi->pt_global_mem || pi->pt_anything) && pi->memory_tag_needed && pi->name_mem_tag) { mark_call_clobbered (pi->name_mem_tag, ESCAPE_IS_GLOBAL); MTAG_GLOBAL (pi->name_mem_tag) = true; } if ((pi->pt_global_mem || pi->pt_anything) && pi->memory_tag_needed && tag) { mark_call_clobbered (tag, ESCAPE_IS_GLOBAL); MTAG_GLOBAL (tag) = true; } } /* If a pt_anything pointer escaped we need to mark all addressable variables call clobbered. */ if (any_pt_anything) { bitmap_iterator bi; unsigned int j; EXECUTE_IF_SET_IN_BITMAP (gimple_addressable_vars (cfun), 0, j, bi) { tree var = referenced_var (j); if (!unmodifiable_var_p (var)) mark_call_clobbered (var, pt_anything_mask); } } } /* Compute which variables need to be marked call clobbered because their tag is call clobbered, and which tags need to be marked global because they contain global variables. */ static void compute_call_clobbered (struct alias_info *ai) { VEC (tree, heap) *worklist = NULL; VEC (int,heap) *worklist2 = NULL; bitmap on_worklist; timevar_push (TV_CALL_CLOBBER); on_worklist = BITMAP_ALLOC (NULL); set_initial_properties (ai); init_transitive_clobber_worklist (&worklist, &worklist2, on_worklist); while (VEC_length (tree, worklist) != 0) { tree curr = VEC_pop (tree, worklist); int reason = VEC_pop (int, worklist2); bitmap_clear_bit (on_worklist, DECL_UID (curr)); mark_call_clobbered (curr, reason); mark_aliases_call_clobbered (curr, &worklist, &worklist2, on_worklist); } VEC_free (tree, heap, worklist); VEC_free (int, heap, worklist2); BITMAP_FREE (on_worklist); compute_tag_properties (); timevar_pop (TV_CALL_CLOBBER); } /* Dump memory partition information to FILE. */ static void dump_memory_partitions (FILE *file) { unsigned i, npart; unsigned long nsyms; tree mpt; fprintf (file, "\nMemory partitions\n\n"); for (i = 0, npart = 0, nsyms = 0; VEC_iterate (tree, gimple_ssa_operands (cfun)->mpt_table, i, mpt); i++) { if (mpt) { bitmap syms = MPT_SYMBOLS (mpt); unsigned long n = (syms) ? bitmap_count_bits (syms) : 0; fprintf (file, "#%u: ", i); print_generic_expr (file, mpt, 0); fprintf (file, ": %lu elements: ", n); dump_decl_set (file, syms); npart++; nsyms += n; } } fprintf (file, "\n%u memory partitions holding %lu symbols\n", npart, nsyms); } /* Dump memory partition information to stderr. */ void debug_memory_partitions (void) { dump_memory_partitions (stderr); } /* Return true if memory partitioning is required given the memory reference estimates in STATS. */ static inline bool need_to_partition_p (struct mem_ref_stats_d *stats) { long num_vops = stats->num_vuses + stats->num_vdefs; long avg_vops = CEIL (num_vops, stats->num_mem_stmts); return (num_vops > (long) MAX_ALIASED_VOPS && avg_vops > (long) AVG_ALIASED_VOPS); } /* Count the actual number of virtual operators in CFUN. Note that this is only meaningful after virtual operands have been populated, so it should be invoked at the end of compute_may_aliases. The number of virtual operators are stored in *NUM_VDEFS_P and *NUM_VUSES_P, the number of partitioned symbols in *NUM_PARTITIONED_P and the number of unpartitioned symbols in *NUM_UNPARTITIONED_P. If any of these pointers is NULL the corresponding count is not computed. */ static void count_mem_refs (long *num_vuses_p, long *num_vdefs_p, long *num_partitioned_p, long *num_unpartitioned_p) { gimple_stmt_iterator gsi; basic_block bb; long num_vdefs, num_vuses, num_partitioned, num_unpartitioned; referenced_var_iterator rvi; tree sym; num_vuses = num_vdefs = num_partitioned = num_unpartitioned = 0; if (num_vuses_p || num_vdefs_p) FOR_EACH_BB (bb) for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { gimple stmt = gsi_stmt (gsi); if (gimple_references_memory_p (stmt)) { num_vuses += NUM_SSA_OPERANDS (stmt, SSA_OP_VUSE); num_vdefs += NUM_SSA_OPERANDS (stmt, SSA_OP_VDEF); } } if (num_partitioned_p || num_unpartitioned_p) FOR_EACH_REFERENCED_VAR (sym, rvi) { if (is_gimple_reg (sym)) continue; if (memory_partition (sym)) num_partitioned++; else num_unpartitioned++; } if (num_vdefs_p) *num_vdefs_p = num_vdefs; if (num_vuses_p) *num_vuses_p = num_vuses; if (num_partitioned_p) *num_partitioned_p = num_partitioned; if (num_unpartitioned_p) *num_unpartitioned_p = num_unpartitioned; } /* The list is sorted by increasing partitioning score (PSCORE). This score is computed such that symbols with high scores are those that are least likely to be partitioned. Given a symbol MP->VAR, PSCORE(S) is the result of the following weighted sum PSCORE(S) = FW * 64 + FR * 32 + DW * 16 + DR * 8 + IW * 4 + IR * 2 + NO_ALIAS where FW Execution frequency of writes to S FR Execution frequency of reads from S DW Number of direct writes to S DR Number of direct reads from S IW Number of indirect writes to S IR Number of indirect reads from S NO_ALIAS State of the NO_ALIAS* flags The basic idea here is that symbols that are frequently written-to in hot paths of the code are the last to be considered for partitioning. */ static inline long mem_sym_score (mem_sym_stats_t mp) { return mp->frequency_writes * 64 + mp->frequency_reads * 32 + mp->num_direct_writes * 16 + mp->num_direct_reads * 8 + mp->num_indirect_writes * 4 + mp->num_indirect_reads * 2 + var_ann (mp->var)->noalias_state; } /* Dump memory reference stats for function CFUN to FILE. */ void dump_mem_ref_stats (FILE *file) { long actual_num_vuses, actual_num_vdefs; long num_partitioned, num_unpartitioned; struct mem_ref_stats_d *stats; stats = gimple_mem_ref_stats (cfun); count_mem_refs (&actual_num_vuses, &actual_num_vdefs, &num_partitioned, &num_unpartitioned); fprintf (file, "\nMemory reference statistics for %s\n\n", lang_hooks.decl_printable_name (current_function_decl, 2)); fprintf (file, "Number of memory statements: %ld\n", stats->num_mem_stmts); fprintf (file, "Number of call sites: %ld\n", stats->num_call_sites); fprintf (file, "Number of pure/const call sites: %ld\n", stats->num_pure_const_call_sites); fprintf (file, "Number of asm sites: %ld\n", stats->num_asm_sites); fprintf (file, "Estimated number of loads: %ld (%ld/stmt)\n", stats->num_vuses, (stats->num_mem_stmts) ? CEIL (stats->num_vuses, stats->num_mem_stmts) : 0); fprintf (file, "Actual number of loads: %ld (%ld/stmt)\n", actual_num_vuses, (stats->num_mem_stmts) ? CEIL (actual_num_vuses, stats->num_mem_stmts) : 0); if (actual_num_vuses > stats->num_vuses + (stats->num_vuses / 25)) fprintf (file, "\t(warning: estimation is lower by more than 25%%)\n"); fprintf (file, "Estimated number of stores: %ld (%ld/stmt)\n", stats->num_vdefs, (stats->num_mem_stmts) ? CEIL (stats->num_vdefs, stats->num_mem_stmts) : 0); fprintf (file, "Actual number of stores: %ld (%ld/stmt)\n", actual_num_vdefs, (stats->num_mem_stmts) ? CEIL (actual_num_vdefs, stats->num_mem_stmts) : 0); if (actual_num_vdefs > stats->num_vdefs + (stats->num_vdefs / 25)) fprintf (file, "\t(warning: estimation is lower by more than 25%%)\n"); fprintf (file, "Partitioning thresholds: MAX = %d AVG = %d " "(%sNEED TO PARTITION)\n", MAX_ALIASED_VOPS, AVG_ALIASED_VOPS, stats->num_mem_stmts && need_to_partition_p (stats) ? "" : "NO "); fprintf (file, "Number of partitioned symbols: %ld\n", num_partitioned); fprintf (file, "Number of unpartitioned symbols: %ld\n", num_unpartitioned); } /* Dump memory reference stats for function FN to stderr. */ void debug_mem_ref_stats (void) { dump_mem_ref_stats (stderr); } /* Dump memory reference stats for variable VAR to FILE. */ static void dump_mem_sym_stats (FILE *file, tree var) { mem_sym_stats_t stats = mem_sym_stats (cfun, var); if (stats == NULL) return; fprintf (file, "read frequency: %6ld, write frequency: %6ld, " "direct reads: %3ld, direct writes: %3ld, " "indirect reads: %4ld, indirect writes: %4ld, symbol: ", stats->frequency_reads, stats->frequency_writes, stats->num_direct_reads, stats->num_direct_writes, stats->num_indirect_reads, stats->num_indirect_writes); print_generic_expr (file, stats->var, 0); fprintf (file, ", tags: "); dump_decl_set (file, stats->parent_tags); } /* Dump memory reference stats for variable VAR to stderr. */ void debug_mem_sym_stats (tree var) { dump_mem_sym_stats (stderr, var); } /* Dump memory reference stats for variable VAR to FILE. For use of tree-dfa.c:dump_variable. */ void dump_mem_sym_stats_for_var (FILE *file, tree var) { mem_sym_stats_t stats = mem_sym_stats (cfun, var); if (stats == NULL) return; fprintf (file, ", score: %ld", mem_sym_score (stats)); fprintf (file, ", direct reads: %ld", stats->num_direct_reads); fprintf (file, ", direct writes: %ld", stats->num_direct_writes); fprintf (file, ", indirect reads: %ld", stats->num_indirect_reads); fprintf (file, ", indirect writes: %ld", stats->num_indirect_writes); } /* Dump memory reference stats for all memory symbols to FILE. */ static void dump_all_mem_sym_stats (FILE *file) { referenced_var_iterator rvi; tree sym; FOR_EACH_REFERENCED_VAR (sym, rvi) { if (is_gimple_reg (sym)) continue; dump_mem_sym_stats (file, sym); } } /* Dump memory reference stats for all memory symbols to stderr. */ void debug_all_mem_sym_stats (void) { dump_all_mem_sym_stats (stderr); } /* Dump the MP_INFO array to FILE. */ static void dump_mp_info (FILE *file, VEC(mem_sym_stats_t,heap) *mp_info) { unsigned i; mem_sym_stats_t mp_p; for (i = 0; VEC_iterate (mem_sym_stats_t, mp_info, i, mp_p); i++) if (!mp_p->partitioned_p) dump_mem_sym_stats (file, mp_p->var); } /* Dump the MP_INFO array to stderr. */ void debug_mp_info (VEC(mem_sym_stats_t,heap) *mp_info) { dump_mp_info (stderr, mp_info); } /* Update memory reference stats for symbol VAR in statement STMT. NUM_DIRECT_READS and NUM_DIRECT_WRITES specify the number of times that VAR is read/written in STMT (indirect reads/writes are not recorded by this function, see compute_memory_partitions). */ void update_mem_sym_stats_from_stmt (tree var, gimple stmt, long num_direct_reads, long num_direct_writes) { mem_sym_stats_t stats; gcc_assert (num_direct_reads >= 0 && num_direct_writes >= 0); stats = get_mem_sym_stats_for (var); stats->num_direct_reads += num_direct_reads; stats->frequency_reads += ((long) gimple_bb (stmt)->frequency * num_direct_reads); stats->num_direct_writes += num_direct_writes; stats->frequency_writes += ((long) gimple_bb (stmt)->frequency * num_direct_writes); } /* Given two MP_INFO entries MP1 and MP2, return -1 if MP1->VAR should be partitioned before MP2->VAR, 0 if they are the same or 1 if MP1->VAR should be partitioned after MP2->VAR. */ static inline int compare_mp_info_entries (mem_sym_stats_t mp1, mem_sym_stats_t mp2) { long pscore1 = mem_sym_score (mp1); long pscore2 = mem_sym_score (mp2); if (pscore1 < pscore2) return -1; else if (pscore1 > pscore2) return 1; else return DECL_UID (mp1->var) - DECL_UID (mp2->var); } /* Comparison routine for qsort. The list is sorted by increasing partitioning score (PSCORE). This score is computed such that symbols with high scores are those that are least likely to be partitioned. */ static int mp_info_cmp (const void *p, const void *q) { mem_sym_stats_t e1 = *((const mem_sym_stats_t *) p); mem_sym_stats_t e2 = *((const mem_sym_stats_t *) q); return compare_mp_info_entries (e1, e2); } /* Sort the array of reference counts used to compute memory partitions. Elements are sorted in ascending order of execution frequency and descending order of virtual operators needed. */ static inline void sort_mp_info (VEC(mem_sym_stats_t,heap) *list) { unsigned num = VEC_length (mem_sym_stats_t, list); if (num < 2) return; if (num == 2) { if (compare_mp_info_entries (VEC_index (mem_sym_stats_t, list, 0), VEC_index (mem_sym_stats_t, list, 1)) > 0) { /* Swap elements if they are in the wrong order. */ mem_sym_stats_t tmp = VEC_index (mem_sym_stats_t, list, 0); VEC_replace (mem_sym_stats_t, list, 0, VEC_index (mem_sym_stats_t, list, 1)); VEC_replace (mem_sym_stats_t, list, 1, tmp); } return; } /* There are 3 or more elements, call qsort. */ qsort (VEC_address (mem_sym_stats_t, list), VEC_length (mem_sym_stats_t, list), sizeof (mem_sym_stats_t), mp_info_cmp); } /* Return the memory partition tag (MPT) associated with memory symbol SYM. */ static tree get_mpt_for (tree sym) { tree mpt; /* Don't create a new tag unnecessarily. */ mpt = memory_partition (sym); if (mpt == NULL_TREE) { mpt = create_tag_raw (MEMORY_PARTITION_TAG, TREE_TYPE (sym), "MPT"); TREE_ADDRESSABLE (mpt) = 0; add_referenced_var (mpt); VEC_safe_push (tree, heap, gimple_ssa_operands (cfun)->mpt_table, mpt); gcc_assert (MPT_SYMBOLS (mpt) == NULL); set_memory_partition (sym, mpt); } return mpt; } /* Add MP_P->VAR to a memory partition and return the partition. */ static tree find_partition_for (mem_sym_stats_t mp_p) { unsigned i; VEC(tree,heap) *mpt_table; tree mpt; mpt_table = gimple_ssa_operands (cfun)->mpt_table; mpt = NULL_TREE; /* Find an existing partition for MP_P->VAR. */ for (i = 0; VEC_iterate (tree, mpt_table, i, mpt); i++) { mem_sym_stats_t mpt_stats; /* If MPT does not have any symbols yet, use it. */ if (MPT_SYMBOLS (mpt) == NULL) break; /* Otherwise, see if MPT has common parent tags with MP_P->VAR, but avoid grouping clobbered variables with non-clobbered variables (otherwise, this tends to creates a single memory partition because other call-clobbered variables may have common parent tags with non-clobbered ones). */ mpt_stats = get_mem_sym_stats_for (mpt); if (mp_p->parent_tags && mpt_stats->parent_tags && is_call_clobbered (mpt) == is_call_clobbered (mp_p->var) && bitmap_intersect_p (mpt_stats->parent_tags, mp_p->parent_tags)) break; /* If no common parent tags are found, see if both MPT and MP_P->VAR are call-clobbered. */ if (is_call_clobbered (mpt) && is_call_clobbered (mp_p->var)) break; } if (mpt == NULL_TREE) mpt = get_mpt_for (mp_p->var); else set_memory_partition (mp_p->var, mpt); mp_p->partitioned_p = true; mark_sym_for_renaming (mp_p->var); mark_sym_for_renaming (mpt); return mpt; } /* Rewrite the alias set for TAG to use the newly created partitions. If TAG is NULL, rewrite the set of call-clobbered variables. NEW_ALIASES is a scratch bitmap to build the new set of aliases for TAG. */ static void rewrite_alias_set_for (tree tag, bitmap new_aliases) { bitmap_iterator bi; unsigned i; tree mpt, sym; EXECUTE_IF_SET_IN_BITMAP (MTAG_ALIASES (tag), 0, i, bi) { sym = referenced_var (i); mpt = memory_partition (sym); if (mpt) bitmap_set_bit (new_aliases, DECL_UID (mpt)); else bitmap_set_bit (new_aliases, DECL_UID (sym)); } /* Rebuild the may-alias array for TAG. */ bitmap_copy (MTAG_ALIASES (tag), new_aliases); } /* Determine how many virtual operands can be saved by partitioning MP_P->VAR into MPT. When a symbol S is thrown inside a partition P, every virtual operand that used to reference S will now reference P. Whether it reduces the number of virtual operands depends on: 1- Direct references to S are never saved. Instead of the virtual operand to S, we will now have a virtual operand to P. 2- Indirect references to S are reduced only for those memory tags holding S that already had other symbols partitioned into P. For instance, if a memory tag T has the alias set { a b S c }, the first time we partition S into P, the alias set will become { a b P c }, so no virtual operands will be saved. However, if we now partition symbol 'c' into P, then the alias set for T will become { a b P }, so we will be saving one virtual operand for every indirect reference to 'c'. 3- Is S is call-clobbered, we save as many virtual operands as call/asm sites exist in the code, but only if other call-clobbered symbols have been grouped into P. The first call-clobbered symbol that we group does not produce any savings. MEM_REF_STATS points to CFUN's memory reference information. */ static void estimate_vop_reduction (struct mem_ref_stats_d *mem_ref_stats, mem_sym_stats_t mp_p, tree mpt) { unsigned i; bitmap_iterator bi; mem_sym_stats_t mpt_stats; /* We should only get symbols with indirect references here. */ gcc_assert (mp_p->num_indirect_reads > 0 || mp_p->num_indirect_writes > 0); /* Note that the only statistics we keep for MPT is the set of parent tags to know which memory tags have had alias members partitioned, and the indicator has_call_clobbered_vars. Reference counts are not important for MPT. */ mpt_stats = get_mem_sym_stats_for (mpt); /* Traverse all the parent tags for MP_P->VAR. For every tag T, if partition P is already grouping aliases of T, then reduce the number of virtual operands by the number of direct references to T. */ if (mp_p->parent_tags) { if (mpt_stats->parent_tags == NULL) mpt_stats->parent_tags = BITMAP_ALLOC (&alias_bitmap_obstack); EXECUTE_IF_SET_IN_BITMAP (mp_p->parent_tags, 0, i, bi) { if (bitmap_bit_p (mpt_stats->parent_tags, i)) { /* Partition MPT is already partitioning symbols in the alias set for TAG. This means that we are now saving 1 virtual operand for every direct reference to TAG. */ tree tag = referenced_var (i); mem_sym_stats_t tag_stats = mem_sym_stats (cfun, tag); mem_ref_stats->num_vuses -= tag_stats->num_direct_reads; mem_ref_stats->num_vdefs -= tag_stats->num_direct_writes; } else { /* This is the first symbol in tag I's alias set that is being grouped under MPT. We will not save any virtual operands this time, but record that MPT is grouping a symbol from TAG's alias set so that the next time we get the savings. */ bitmap_set_bit (mpt_stats->parent_tags, i); } } } /* If MP_P->VAR is call-clobbered, and MPT is already grouping call-clobbered symbols, then we will save as many virtual operands as asm/call sites there are. */ if (is_call_clobbered (mp_p->var)) { if (mpt_stats->has_call_clobbered_vars) mem_ref_stats->num_vdefs -= mem_ref_stats->num_call_sites + mem_ref_stats->num_asm_sites; else mpt_stats->has_call_clobbered_vars = true; } } /* Helper for compute_memory_partitions. Transfer reference counts from pointers to their pointed-to sets. Counters for pointers were computed by update_alias_info. MEM_REF_STATS points to CFUN's memory reference information. */ static void update_reference_counts (struct mem_ref_stats_d *mem_ref_stats) { unsigned i; bitmap_iterator bi; mem_sym_stats_t sym_stats; for (i = 1; i < num_ssa_names; i++) { tree ptr; struct ptr_info_def *pi; ptr = ssa_name (i); if (ptr && POINTER_TYPE_P (TREE_TYPE (ptr)) && (pi = SSA_NAME_PTR_INFO (ptr)) != NULL && pi->memory_tag_needed) { unsigned j; bitmap_iterator bj; tree tag; mem_sym_stats_t ptr_stats, tag_stats; /* If PTR has flow-sensitive points-to information, use PTR's name tag, otherwise use the symbol tag associated with PTR's symbol. */ if (pi->name_mem_tag) tag = pi->name_mem_tag; else tag = symbol_mem_tag (SSA_NAME_VAR (ptr)); ptr_stats = get_mem_sym_stats_for (ptr); tag_stats = get_mem_sym_stats_for (tag); /* TAG has as many direct references as dereferences we found for its parent pointer. */ tag_stats->num_direct_reads += ptr_stats->num_direct_reads; tag_stats->num_direct_writes += ptr_stats->num_direct_writes; /* All the dereferences of pointer PTR are considered direct references to PTR's memory tag (TAG). In turn, references to TAG will become virtual operands for every symbol in TAG's alias set. So, for every symbol ALIAS in TAG's alias set, add as many indirect references to ALIAS as direct references there are for TAG. */ if (MTAG_ALIASES (tag)) EXECUTE_IF_SET_IN_BITMAP (MTAG_ALIASES (tag), 0, j, bj) { tree alias = referenced_var (j); sym_stats = get_mem_sym_stats_for (alias); /* All the direct references to TAG are indirect references to ALIAS. */ sym_stats->num_indirect_reads += ptr_stats->num_direct_reads; sym_stats->num_indirect_writes += ptr_stats->num_direct_writes; sym_stats->frequency_reads += ptr_stats->frequency_reads; sym_stats->frequency_writes += ptr_stats->frequency_writes; /* Indicate that TAG is one of ALIAS's parent tags. */ if (sym_stats->parent_tags == NULL) sym_stats->parent_tags = BITMAP_ALLOC (&alias_bitmap_obstack); bitmap_set_bit (sym_stats->parent_tags, DECL_UID (tag)); } } } /* Call-clobbered symbols are indirectly written at every call/asm site. */ EXECUTE_IF_SET_IN_BITMAP (gimple_call_clobbered_vars (cfun), 0, i, bi) { tree sym = referenced_var (i); sym_stats = get_mem_sym_stats_for (sym); sym_stats->num_indirect_writes += mem_ref_stats->num_call_sites + mem_ref_stats->num_asm_sites; } /* Addressable symbols are indirectly written at some ASM sites. Since only ASM sites that clobber memory actually affect addressable symbols, this is an over-estimation. */ EXECUTE_IF_SET_IN_BITMAP (gimple_addressable_vars (cfun), 0, i, bi) { tree sym = referenced_var (i); sym_stats = get_mem_sym_stats_for (sym); sym_stats->num_indirect_writes += mem_ref_stats->num_asm_sites; } } /* Helper for compute_memory_partitions. Add all memory symbols to *MP_INFO_P and compute the initial estimate for the total number of virtual operands needed. MEM_REF_STATS points to CFUN's memory reference information. On exit, *TAGS_P will contain the list of memory tags whose alias set need to be rewritten after partitioning. */ static void build_mp_info (struct mem_ref_stats_d *mem_ref_stats, VEC(mem_sym_stats_t,heap) **mp_info_p, VEC(tree,heap) **tags_p) { tree var; referenced_var_iterator rvi; FOR_EACH_REFERENCED_VAR (var, rvi) { mem_sym_stats_t sym_stats; tree old_mpt; /* We are only interested in memory symbols other than MPTs. */ if (is_gimple_reg (var) || TREE_CODE (var) == MEMORY_PARTITION_TAG) continue; /* Collect memory tags into the TAGS array so that we can rewrite their alias sets after partitioning. */ if (MTAG_P (var) && MTAG_ALIASES (var)) VEC_safe_push (tree, heap, *tags_p, var); /* Since we are going to re-compute partitions, any symbols that used to belong to a partition must be detached from it and marked for renaming. */ if ((old_mpt = memory_partition (var)) != NULL) { mark_sym_for_renaming (old_mpt); set_memory_partition (var, NULL_TREE); mark_sym_for_renaming (var); } sym_stats = get_mem_sym_stats_for (var); /* Add VAR's reference info to MP_INFO. Note that the only symbols that make sense to partition are those that have indirect references. If a symbol S is always directly referenced, partitioning it will not reduce the number of virtual operators. The only symbols that are profitable to partition are those that belong to alias sets and/or are call-clobbered. */ if (sym_stats->num_indirect_reads > 0 || sym_stats->num_indirect_writes > 0) VEC_safe_push (mem_sym_stats_t, heap, *mp_info_p, sym_stats); /* Update the number of estimated VOPS. Note that direct references to memory tags are always counted as indirect references to their alias set members, so if a memory tag has aliases, do not count its direct references to avoid double accounting. */ if (!MTAG_P (var) || !MTAG_ALIASES (var)) { mem_ref_stats->num_vuses += sym_stats->num_direct_reads; mem_ref_stats->num_vdefs += sym_stats->num_direct_writes; } mem_ref_stats->num_vuses += sym_stats->num_indirect_reads; mem_ref_stats->num_vdefs += sym_stats->num_indirect_writes; } } /* Compute memory partitions. A memory partition (MPT) is an arbitrary grouping of memory symbols, such that references to one member of the group is considered a reference to all the members of the group. As opposed to alias sets in memory tags, the grouping into partitions is completely arbitrary and only done to reduce the number of virtual operands. The only rule that needs to be observed when creating memory partitions is that given two memory partitions MPT.i and MPT.j, they must not contain symbols in common. Memory partitions are used when putting the program into Memory-SSA form. In particular, in Memory-SSA PHI nodes are not computed for individual memory symbols. They are computed for memory partitions. This reduces the amount of PHI nodes in the SSA graph at the expense of precision (i.e., it makes unrelated stores affect each other). However, it is possible to increase precision by changing this partitioning scheme. For instance, if the partitioning scheme is such that get_mpt_for is the identity function (that is, get_mpt_for (s) = s), this will result in ultimate precision at the expense of huge SSA webs. At the other extreme, a partitioning scheme that groups all the symbols in the same set results in minimal SSA webs and almost total loss of precision. There partitioning heuristic uses three parameters to decide the order in which symbols are processed. The list of symbols is sorted so that symbols that are more likely to be partitioned are near the top of the list: - Execution frequency. If a memory references is in a frequently executed code path, grouping it into a partition may block useful transformations and cause sub-optimal code generation. So, the partition heuristic tries to avoid grouping symbols with high execution frequency scores. Execution frequency is taken directly from the basic blocks where every reference is made (see update_mem_sym_stats_from_stmt), which in turn uses the profile guided machinery, so if the program is compiled with PGO enabled, more accurate partitioning decisions will be made. - Number of references. Symbols with few references in the code, are partitioned before symbols with many references. - NO_ALIAS attributes. Symbols with any of the NO_ALIAS* attributes are partitioned after symbols marked MAY_ALIAS. Once the list is sorted, the partitioning proceeds as follows: 1- For every symbol S in MP_INFO, create a new memory partition MP, if necessary. To avoid memory partitions that contain symbols from non-conflicting alias sets, memory partitions are associated to the memory tag that holds S in its alias set. So, when looking for a memory partition for S, the memory partition associated with one of the memory tags holding S is chosen. If none exists, a new one is created. 2- Add S to memory partition MP. 3- Reduce by 1 the number of VOPS for every memory tag holding S. 4- If the total number of VOPS is less than MAX_ALIASED_VOPS or the average number of VOPS per statement is less than AVG_ALIASED_VOPS, stop. Otherwise, go to the next symbol in the list. */ static void compute_memory_partitions (void) { tree tag; unsigned i; mem_sym_stats_t mp_p; VEC(mem_sym_stats_t,heap) *mp_info; bitmap new_aliases; VEC(tree,heap) *tags; struct mem_ref_stats_d *mem_ref_stats; int prev_max_aliased_vops; mem_ref_stats = gimple_mem_ref_stats (cfun); gcc_assert (mem_ref_stats->num_vuses == 0 && mem_ref_stats->num_vdefs == 0); if (mem_ref_stats->num_mem_stmts == 0) return; timevar_push (TV_MEMORY_PARTITIONING); mp_info = NULL; tags = NULL; prev_max_aliased_vops = MAX_ALIASED_VOPS; /* Since we clearly cannot lower the number of virtual operators below the total number of memory statements in the function, we may need to adjust MAX_ALIASED_VOPS beforehand. */ if (MAX_ALIASED_VOPS < mem_ref_stats->num_mem_stmts) MAX_ALIASED_VOPS = mem_ref_stats->num_mem_stmts; /* Update reference stats for all the pointed-to variables and memory tags. */ update_reference_counts (mem_ref_stats); /* Add all the memory symbols to MP_INFO. */ build_mp_info (mem_ref_stats, &mp_info, &tags); /* No partitions required if we are below the threshold. */ if (!need_to_partition_p (mem_ref_stats)) { if (dump_file) fprintf (dump_file, "\nMemory partitioning NOT NEEDED for %s\n", get_name (current_function_decl)); goto done; } /* Sort the MP_INFO array so that symbols that should be partitioned first are near the top of the list. */ sort_mp_info (mp_info); if (dump_file) { fprintf (dump_file, "\nMemory partitioning NEEDED for %s\n\n", get_name (current_function_decl)); fprintf (dump_file, "Memory symbol references before partitioning:\n"); dump_mp_info (dump_file, mp_info); } /* Create partitions for variables in MP_INFO until we have enough to lower the total number of VOPS below MAX_ALIASED_VOPS or if the average number of VOPS per statement is below AVG_ALIASED_VOPS. */ for (i = 0; VEC_iterate (mem_sym_stats_t, mp_info, i, mp_p); i++) { tree mpt; /* If we are below the threshold, stop. */ if (!need_to_partition_p (mem_ref_stats)) break; mpt = find_partition_for (mp_p); estimate_vop_reduction (mem_ref_stats, mp_p, mpt); } /* After partitions have been created, rewrite alias sets to use them instead of the original symbols. This way, if the alias set was computed as { a b c d e f }, and the subset { b e f } was grouped into partition MPT.3, then the new alias set for the tag will be { a c d MPT.3 }. Note that this is not strictly necessary. The operand scanner will always check if a symbol belongs to a partition when adding virtual operands. However, by reducing the size of the alias sets to be scanned, the work needed inside the operand scanner is significantly reduced. */ new_aliases = BITMAP_ALLOC (&alias_bitmap_obstack); for (i = 0; VEC_iterate (tree, tags, i, tag); i++) { rewrite_alias_set_for (tag, new_aliases); bitmap_clear (new_aliases); } BITMAP_FREE (new_aliases); if (dump_file) { fprintf (dump_file, "\nMemory symbol references after partitioning:\n"); dump_mp_info (dump_file, mp_info); } done: /* Free allocated memory. */ VEC_free (mem_sym_stats_t, heap, mp_info); VEC_free (tree, heap, tags); MAX_ALIASED_VOPS = prev_max_aliased_vops; timevar_pop (TV_MEMORY_PARTITIONING); } /* Compute may-alias information for every variable referenced in function FNDECL. Alias analysis proceeds in 3 main phases: 1- Points-to and escape analysis. This phase walks the use-def chains in the SSA web looking for three things: * Assignments of the form P_i = &VAR * Assignments of the form P_i = malloc() * Pointers and ADDR_EXPR that escape the current function. The concept of 'escaping' is the same one used in the Java world. When a pointer or an ADDR_EXPR escapes, it means that it has been exposed outside of the current function. So, assignment to global variables, function arguments and returning a pointer are all escape sites, as are conversions between pointers and integers. This is where we are currently limited. Since not everything is renamed into SSA, we lose track of escape properties when a pointer is stashed inside a field in a structure, for instance. In those cases, we are assuming that the pointer does escape. We use escape analysis to determine whether a variable is call-clobbered. Simply put, if an ADDR_EXPR escapes, then the variable is call-clobbered. If a pointer P_i escapes, then all the variables pointed-to by P_i (and its memory tag) also escape. 2- Compute flow-sensitive aliases We have two classes of memory tags. Memory tags associated with the pointed-to data type of the pointers in the program. These tags are called "symbol memory tag" (SMT). The other class are those associated with SSA_NAMEs, called "name memory tag" (NMT). The basic idea is that when adding operands for an INDIRECT_REF *P_i, we will first check whether P_i has a name tag, if it does we use it, because that will have more precise aliasing information. Otherwise, we use the standard symbol tag. In this phase, we go through all the pointers we found in points-to analysis and create alias sets for the name memory tags associated with each pointer P_i. If P_i escapes, we mark call-clobbered the variables it points to and its tag. 3- Compute flow-insensitive aliases This pass will compare the alias set of every symbol memory tag and every addressable variable found in the program. Given a symbol memory tag SMT and an addressable variable V. If the alias sets of SMT and V conflict (as computed by may_alias_p), then V is marked as an alias tag and added to the alias set of SMT. For instance, consider the following function: foo (int i) { int *p, a, b; if (i > 10) p = &a; else p = &b; *p = 3; a = b + 2; return *p; } After aliasing analysis has finished, the symbol memory tag for pointer 'p' will have two aliases, namely variables 'a' and 'b'. Every time pointer 'p' is dereferenced, we want to mark the operation as a potential reference to 'a' and 'b'. foo (int i) { int *p, a, b; if (i_2 > 10) p_4 = &a; else p_6 = &b; # p_1 = PHI ; # a_7 = VDEF ; # b_8 = VDEF ; *p_1 = 3; # a_9 = VDEF # VUSE a_9 = b_8 + 2; # VUSE ; # VUSE ; return *p_1; } In certain cases, the list of may aliases for a pointer may grow too large. This may cause an explosion in the number of virtual operands inserted in the code. Resulting in increased memory consumption and compilation time. When the number of virtual operands needed to represent aliased loads and stores grows too large (configurable with option --param max-aliased-vops and --param avg-aliased-vops), alias sets are grouped to avoid severe compile-time slow downs and memory consumption. See compute_memory_partitions. */ unsigned int compute_may_aliases (void) { struct alias_info *ai; timevar_push (TV_TREE_MAY_ALIAS); memset (&alias_stats, 0, sizeof (alias_stats)); /* Initialize aliasing information. */ ai = init_alias_info (); /* For each pointer P_i, determine the sets of variables that P_i may point-to. For every addressable variable V, determine whether the address of V escapes the current function, making V call-clobbered (i.e., whether &V is stored in a global variable or if its passed as a function call argument). */ compute_points_to_sets (); /* Update various related attributes like escaped addresses, pointer dereferences for loads and stores. This is used when creating name tags and alias sets. */ update_alias_info (ai); /* Collect all pointers and addressable variables, compute alias sets, create memory tags for pointers and promote variables whose address is not needed anymore. */ setup_pointers_and_addressables (ai); /* Compute type-based flow-insensitive aliasing for all the type memory tags. */ compute_flow_insensitive_aliasing (ai); /* Compute flow-sensitive, points-to based aliasing for all the name memory tags. */ compute_flow_sensitive_aliasing (ai); /* Compute call clobbering information. */ compute_call_clobbered (ai); /* If the program makes no reference to global variables, but it contains a mixture of pure and non-pure functions, then we need to create use-def and def-def links between these functions to avoid invalid transformations on them. */ maybe_create_global_var (); /* Compute memory partitions for every memory variable. */ compute_memory_partitions (); /* Remove partitions with no symbols. Partitions may end up with an empty MPT_SYMBOLS set if a previous round of alias analysis needed to partition more symbols. Since we don't need those partitions anymore, remove them to free up the space. */ { tree mpt; unsigned i; VEC(tree,heap) *mpt_table; mpt_table = gimple_ssa_operands (cfun)->mpt_table; i = 0; while (i < VEC_length (tree, mpt_table)) { mpt = VEC_index (tree, mpt_table, i); if (MPT_SYMBOLS (mpt) == NULL) VEC_unordered_remove (tree, mpt_table, i); else i++; } } /* Populate all virtual operands and newly promoted register operands. */ { gimple_stmt_iterator gsi; basic_block bb; FOR_EACH_BB (bb) for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) update_stmt_if_modified (gsi_stmt (gsi)); } /* Debugging dumps. */ if (dump_file) { dump_mem_ref_stats (dump_file); dump_alias_info (dump_file); dump_points_to_info (dump_file); if (dump_flags & TDF_STATS) dump_alias_stats (dump_file); if (dump_flags & TDF_DETAILS) dump_referenced_vars (dump_file); } /* Deallocate memory used by aliasing data structures. */ delete_alias_info (ai); if (need_ssa_update_p ()) update_ssa (TODO_update_ssa); timevar_pop (TV_TREE_MAY_ALIAS); return 0; } /* Data structure used to count the number of dereferences to PTR inside an expression. */ struct count_ptr_d { tree ptr; unsigned num_stores; unsigned num_loads; }; /* Helper for count_uses_and_derefs. Called by walk_tree to look for (ALIGN/MISALIGNED_)INDIRECT_REF nodes for the pointer passed in DATA. */ static tree count_ptr_derefs (tree *tp, int *walk_subtrees, void *data) { struct walk_stmt_info *wi_p = (struct walk_stmt_info *) data; struct count_ptr_d *count_p = (struct count_ptr_d *) wi_p->info; /* Do not walk inside ADDR_EXPR nodes. In the expression &ptr->fld, pointer 'ptr' is *not* dereferenced, it is simply used to compute the address of 'fld' as 'ptr + offsetof(fld)'. */ if (TREE_CODE (*tp) == ADDR_EXPR) { *walk_subtrees = 0; return NULL_TREE; } if (INDIRECT_REF_P (*tp) && TREE_OPERAND (*tp, 0) == count_p->ptr) { if (wi_p->is_lhs) count_p->num_stores++; else count_p->num_loads++; } return NULL_TREE; } /* Count the number of direct and indirect uses for pointer PTR in statement STMT. The number of direct uses is stored in *NUM_USES_P. Indirect references are counted separately depending on whether they are store or load operations. The counts are stored in *NUM_STORES_P and *NUM_LOADS_P. */ void count_uses_and_derefs (tree ptr, gimple stmt, unsigned *num_uses_p, unsigned *num_loads_p, unsigned *num_stores_p) { ssa_op_iter i; tree use; *num_uses_p = 0; *num_loads_p = 0; *num_stores_p = 0; /* Find out the total number of uses of PTR in STMT. */ FOR_EACH_SSA_TREE_OPERAND (use, stmt, i, SSA_OP_USE) if (use == ptr) (*num_uses_p)++; /* Now count the number of indirect references to PTR. This is truly awful, but we don't have much choice. There are no parent pointers inside INDIRECT_REFs, so an expression like '*x_1 = foo (x_1, *x_1)' needs to be traversed piece by piece to find all the indirect and direct uses of x_1 inside. The only shortcut we can take is the fact that GIMPLE only allows INDIRECT_REFs inside the expressions below. */ if (is_gimple_assign (stmt) || gimple_code (stmt) == GIMPLE_RETURN || gimple_code (stmt) == GIMPLE_ASM || is_gimple_call (stmt)) { struct walk_stmt_info wi; struct count_ptr_d count; count.ptr = ptr; count.num_stores = 0; count.num_loads = 0; memset (&wi, 0, sizeof (wi)); wi.info = &count; walk_gimple_op (stmt, count_ptr_derefs, &wi); *num_stores_p = count.num_stores; *num_loads_p = count.num_loads; } gcc_assert (*num_uses_p >= *num_loads_p + *num_stores_p); } /* Remove memory references stats for function FN. */ void delete_mem_ref_stats (struct function *fn) { if (gimple_mem_ref_stats (fn)->mem_sym_stats) { free_alloc_pool (mem_sym_stats_pool); pointer_map_destroy (gimple_mem_ref_stats (fn)->mem_sym_stats); } gimple_mem_ref_stats (fn)->mem_sym_stats = NULL; } /* Initialize memory reference stats. */ static void init_mem_ref_stats (void) { struct mem_ref_stats_d *mem_ref_stats = gimple_mem_ref_stats (cfun); mem_sym_stats_pool = create_alloc_pool ("Mem sym stats", sizeof (struct mem_sym_stats_d), 100); memset (mem_ref_stats, 0, sizeof (struct mem_ref_stats_d)); mem_ref_stats->mem_sym_stats = pointer_map_create (); } /* Helper for init_alias_info. Reset existing aliasing information. */ static void reset_alias_info (void) { referenced_var_iterator rvi; tree var; unsigned i; bitmap active_nmts, all_nmts; /* Clear the set of addressable variables. We do not need to clear the TREE_ADDRESSABLE bit on every symbol because we are going to re-compute addressability here. */ bitmap_clear (gimple_addressable_vars (cfun)); active_nmts = BITMAP_ALLOC (&alias_bitmap_obstack); all_nmts = BITMAP_ALLOC (&alias_bitmap_obstack); /* Clear flow-insensitive alias information from each symbol. */ FOR_EACH_REFERENCED_VAR (var, rvi) { if (is_gimple_reg (var)) continue; if (MTAG_P (var)) MTAG_ALIASES (var) = NULL; /* Memory partition information will be computed from scratch. */ if (TREE_CODE (var) == MEMORY_PARTITION_TAG) MPT_SYMBOLS (var) = NULL; /* Collect all the name tags to determine if we have any orphaned that need to be removed from the IL. A name tag will be orphaned if it is not associated with any active SSA name. */ if (TREE_CODE (var) == NAME_MEMORY_TAG) bitmap_set_bit (all_nmts, DECL_UID (var)); /* Since we are about to re-discover call-clobbered variables, clear the call-clobbered flag. */ clear_call_clobbered (var); } /* There should be no call-clobbered variable left. */ gcc_assert (bitmap_empty_p (gimple_call_clobbered_vars (cfun))); /* Clear the call-used variables. */ bitmap_clear (gimple_call_used_vars (cfun)); /* Clear flow-sensitive points-to information from each SSA name. */ for (i = 1; i < num_ssa_names; i++) { tree name = ssa_name (i); if (!name || !POINTER_TYPE_P (TREE_TYPE (name))) continue; if (SSA_NAME_PTR_INFO (name)) { struct ptr_info_def *pi = SSA_NAME_PTR_INFO (name); /* Clear all the flags but keep the name tag to avoid creating new temporaries unnecessarily. If this pointer is found to point to a subset or superset of its former points-to set, then a new tag will need to be created in create_name_tags. */ pi->pt_anything = 0; pi->pt_null = 0; pi->value_escapes_p = 0; pi->memory_tag_needed = 0; pi->is_dereferenced = 0; if (pi->pt_vars) bitmap_clear (pi->pt_vars); /* Add NAME's name tag to the set of active tags. */ if (pi->name_mem_tag) bitmap_set_bit (active_nmts, DECL_UID (pi->name_mem_tag)); } } /* Name memory tags that are no longer associated with an SSA name are considered stale and should be removed from the IL. All the name tags that are in the set ALL_NMTS but not in ACTIVE_NMTS are considered stale and marked for renaming. */ bitmap_and_compl_into (all_nmts, active_nmts); mark_set_for_renaming (all_nmts); BITMAP_FREE (all_nmts); BITMAP_FREE (active_nmts); } /* Initialize the data structures used for alias analysis. */ static struct alias_info * init_alias_info (void) { struct alias_info *ai; referenced_var_iterator rvi; tree var; static bool alias_bitmap_obstack_initialized; ai = XCNEW (struct alias_info); ai->ssa_names_visited = sbitmap_alloc (num_ssa_names); sbitmap_zero (ai->ssa_names_visited); ai->processed_ptrs = VEC_alloc (tree, heap, 50); ai->dereferenced_ptrs = pointer_set_create (); /* Clear out all memory reference stats. */ init_mem_ref_stats (); /* If aliases have been computed before, clear existing information. */ if (gimple_aliases_computed_p (cfun)) reset_alias_info (); else { /* If this is the first time we compute aliasing information, every non-register symbol will need to be put into SSA form (the initial SSA form only operates on GIMPLE registers). */ FOR_EACH_REFERENCED_VAR (var, rvi) if (!is_gimple_reg (var)) mark_sym_for_renaming (var); } /* Next time, we will need to reset alias information. */ cfun->gimple_df->aliases_computed_p = true; if (alias_bitmap_obstack_initialized) bitmap_obstack_release (&alias_bitmap_obstack); bitmap_obstack_initialize (&alias_bitmap_obstack); alias_bitmap_obstack_initialized = true; return ai; } /* Deallocate memory used by alias analysis. */ static void delete_alias_info (struct alias_info *ai) { size_t i; sbitmap_free (ai->ssa_names_visited); VEC_free (tree, heap, ai->processed_ptrs); for (i = 0; i < ai->num_addressable_vars; i++) free (ai->addressable_vars[i]); free (ai->addressable_vars); for (i = 0; i < ai->num_pointers; i++) free (ai->pointers[i]); free (ai->pointers); pointer_set_destroy (ai->dereferenced_ptrs); free (ai); delete_mem_ref_stats (cfun); delete_points_to_sets (); } /* Used for hashing to identify pointer infos with identical pt_vars bitmaps. */ static int eq_ptr_info (const void *p1, const void *p2) { const struct ptr_info_def *n1 = (const struct ptr_info_def *) p1; const struct ptr_info_def *n2 = (const struct ptr_info_def *) p2; return bitmap_equal_p (n1->pt_vars, n2->pt_vars); } static hashval_t ptr_info_hash (const void *p) { const struct ptr_info_def *n = (const struct ptr_info_def *) p; return bitmap_hash (n->pt_vars); } /* Create name tags for all the pointers that have been dereferenced. We only create a name tag for a pointer P if P is found to point to a set of variables (so that we can alias them to *P) or if it is the result of a call to malloc (which means that P cannot point to anything else nor alias any other variable). If two pointers P and Q point to the same set of variables, they are assigned the same name tag. */ static void create_name_tags (void) { size_t i; VEC (tree, heap) *with_ptvars = NULL; tree ptr; htab_t ptr_hash; /* Collect the list of pointers with a non-empty points to set. */ for (i = 1; i < num_ssa_names; i++) { tree ptr = ssa_name (i); struct ptr_info_def *pi; if (!ptr || !POINTER_TYPE_P (TREE_TYPE (ptr)) || !SSA_NAME_PTR_INFO (ptr)) continue; pi = SSA_NAME_PTR_INFO (ptr); if (pi->pt_anything || !pi->memory_tag_needed) { /* No name tags for pointers that have not been dereferenced or point to an arbitrary location. */ pi->name_mem_tag = NULL_TREE; continue; } /* Set pt_anything on the pointers without pt_vars filled in so that they are assigned a symbol tag. */ if (pi->pt_vars && !bitmap_empty_p (pi->pt_vars)) VEC_safe_push (tree, heap, with_ptvars, ptr); else set_pt_anything (ptr); } /* If we didn't find any pointers with pt_vars set, we're done. */ if (!with_ptvars) return; ptr_hash = htab_create (10, ptr_info_hash, eq_ptr_info, NULL); /* Now go through the pointers with pt_vars, and find a name tag with the same pt_vars as this pointer, or create one if one doesn't exist. */ for (i = 0; VEC_iterate (tree, with_ptvars, i, ptr); i++) { struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr); tree old_name_tag = pi->name_mem_tag; struct ptr_info_def **slot; /* If PTR points to a set of variables, check if we don't have another pointer Q with the same points-to set before creating a tag. If so, use Q's tag instead of creating a new one. This is important for not creating unnecessary symbols and also for copy propagation. If we ever need to propagate PTR into Q or vice-versa, we would run into problems if they both had different name tags because they would have different SSA version numbers (which would force us to take the name tags in and out of SSA). */ slot = (struct ptr_info_def **) htab_find_slot (ptr_hash, pi, INSERT); if (*slot) pi->name_mem_tag = (*slot)->name_mem_tag; else { *slot = pi; /* If we didn't find a pointer with the same points-to set as PTR, create a new name tag if needed. */ if (pi->name_mem_tag == NULL_TREE) pi->name_mem_tag = get_nmt_for (ptr); } /* If the new name tag computed for PTR is different than the old name tag that it used to have, then the old tag needs to be removed from the IL, so we mark it for renaming. */ if (old_name_tag && old_name_tag != pi->name_mem_tag) mark_sym_for_renaming (old_name_tag); /* Inherit volatility from the pointed-to type. */ TREE_THIS_VOLATILE (pi->name_mem_tag) |= TYPE_VOLATILE (TREE_TYPE (TREE_TYPE (ptr))); /* Mark the new name tag for renaming. */ mark_sym_for_renaming (pi->name_mem_tag); } htab_delete (ptr_hash); VEC_free (tree, heap, with_ptvars); } /* Union the alias set SET into the may-aliases for TAG. */ static void union_alias_set_into (tree tag, bitmap set) { bitmap ma = MTAG_ALIASES (tag); if (bitmap_empty_p (set)) return; if (!ma) ma = MTAG_ALIASES (tag) = BITMAP_ALLOC (&alias_bitmap_obstack); bitmap_ior_into (ma, set); } /* For every pointer P_i in AI->PROCESSED_PTRS, create may-alias sets for the name memory tag (NMT) associated with P_i. If P_i escapes, then its name tag and the variables it points-to are call-clobbered. Finally, if P_i escapes and we could not determine where it points to, then all the variables in the same alias set as *P_i are marked call-clobbered. This is necessary because we must assume that P_i may take the address of any variable in the same alias set. */ static void compute_flow_sensitive_aliasing (struct alias_info *ai) { size_t i; tree ptr; timevar_push (TV_FLOW_SENSITIVE); for (i = 0; VEC_iterate (tree, ai->processed_ptrs, i, ptr); i++) { if (!find_what_p_points_to (ptr)) set_pt_anything (ptr); } create_name_tags (); for (i = 0; VEC_iterate (tree, ai->processed_ptrs, i, ptr); i++) { struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr); /* Set up aliasing information for PTR's name memory tag (if it has one). Note that only pointers that have been dereferenced will have a name memory tag. */ if (pi->name_mem_tag && pi->pt_vars) { if (!bitmap_empty_p (pi->pt_vars)) union_alias_set_into (pi->name_mem_tag, pi->pt_vars); } } timevar_pop (TV_FLOW_SENSITIVE); } /* Return TRUE if at least one symbol in TAG2's alias set is also present in TAG1's alias set. */ static bool have_common_aliases_p (bitmap tag1aliases, bitmap tag2aliases) { /* This is the old behavior of have_common_aliases_p, which is to return false if both sets are empty, or one set is and the other isn't. */ if (tag1aliases == NULL || tag2aliases == NULL) return false; return bitmap_intersect_p (tag1aliases, tag2aliases); } /* Compute type-based alias sets. Traverse all the pointers and addressable variables found in setup_pointers_and_addressables. For every pointer P in AI->POINTERS and addressable variable V in AI->ADDRESSABLE_VARS, add V to the may-alias sets of P's symbol memory tag (SMT) if their alias sets conflict. V is then marked as an aliased symbol so that the operand scanner knows that statements containing V have aliased operands. */ static void compute_flow_insensitive_aliasing (struct alias_info *ai) { referenced_var_iterator rvi; tree var; size_t i; timevar_push (TV_FLOW_INSENSITIVE); /* Since this analysis is based exclusively on symbols, it fails to handle cases where two pointers P and Q have different memory tags with conflicting alias set numbers but no aliased symbols in common. For example, suppose that we have two memory tags SMT.1 and SMT.2 such that may-aliases (SMT.1) = { a } may-aliases (SMT.2) = { b } and the alias set number of SMT.1 conflicts with that of SMT.2. Since they don't have symbols in common, loads and stores from SMT.1 and SMT.2 will seem independent of each other, which will lead to the optimizers making invalid transformations (see testsuite/gcc.c-torture/execute/pr15262-[12].c). To avoid this problem, we do a final traversal of AI->POINTERS looking for pairs of pointers that have no aliased symbols in common and yet have conflicting alias set numbers. Note this has to be done first as we only can avoid adding aliases for common memory tag aliases, not for common symbol aliases as they might get pruned by the operand scanner later. */ for (i = 0; i < ai->num_pointers; i++) { size_t j; struct alias_map_d *p_map1 = ai->pointers[i]; tree tag1 = symbol_mem_tag (p_map1->var); bitmap may_aliases1 = MTAG_ALIASES (tag1); for (j = 0; j < ai->num_pointers; j++) { struct alias_map_d *p_map2 = ai->pointers[j]; tree tag2 = symbol_mem_tag (p_map2->var); bitmap may_aliases2 = may_aliases (tag2); /* By convention tags don't alias themselves. */ if (tag1 == tag2) continue; /* If the pointers may not point to each other, do nothing. */ if (!may_alias_p (p_map1->var, p_map1->set, tag2, p_map2->set, true)) continue; /* The two pointers may alias each other. If they already have symbols in common, do nothing. */ if (have_common_aliases_p (may_aliases1, may_aliases2)) continue; add_may_alias (tag1, tag2); } } /* For every pointer P, determine which addressable variables may alias with P's symbol memory tag. */ for (i = 0; i < ai->num_pointers; i++) { size_t j; struct alias_map_d *p_map = ai->pointers[i]; tree tag = symbol_mem_tag (p_map->var); tree var; for (j = 0; j < ai->num_addressable_vars; j++) { struct alias_map_d *v_map; var_ann_t v_ann; v_map = ai->addressable_vars[j]; var = v_map->var; v_ann = var_ann (var); /* We used to skip variables that have never been written to if the memory tag has been never written to directly (or either of them were call clobbered). This is not enough though, as this misses writes through the tags aliases. So, for correctness we need to include any aliased variable here. */ if (may_alias_p (p_map->var, p_map->set, var, v_map->set, false)) { /* Add VAR to TAG's may-aliases set. */ add_may_alias (tag, var); } } } /* We have to add all HEAP variables to all SMTs aliases bitmaps. As we don't know which effective type the HEAP will have we cannot do better here and we need the conflicts with obfuscated pointers (a simple (*(int[n] *)ptr)[i] will do, with ptr from a VLA array allocation). */ for (i = 0; i < ai->num_pointers; i++) { struct alias_map_d *p_map = ai->pointers[i]; tree tag = symbol_mem_tag (p_map->var); FOR_EACH_REFERENCED_VAR (var, rvi) { if (var_ann (var)->is_heapvar) add_may_alias (tag, var); } } timevar_pop (TV_FLOW_INSENSITIVE); } /* Create a new alias set entry for VAR in AI->ADDRESSABLE_VARS. */ static void create_alias_map_for (tree var, struct alias_info *ai) { struct alias_map_d *alias_map; alias_map = XCNEW (struct alias_map_d); alias_map->var = var; alias_map->set = get_alias_set (var); ai->addressable_vars[ai->num_addressable_vars++] = alias_map; } /* Update related alias information kept in AI. This is used when building name tags, alias sets and deciding grouping heuristics. STMT is the statement to process. This function also updates ADDRESSABLE_VARS. */ static void update_alias_info_1 (gimple stmt, struct alias_info *ai) { bitmap addr_taken; use_operand_p use_p; ssa_op_iter iter; bool stmt_dereferences_ptr_p; enum escape_type stmt_escape_type = is_escape_site (stmt); struct mem_ref_stats_d *mem_ref_stats = gimple_mem_ref_stats (cfun); stmt_dereferences_ptr_p = false; if (stmt_escape_type == ESCAPE_TO_CALL || stmt_escape_type == ESCAPE_TO_PURE_CONST) { mem_ref_stats->num_call_sites++; if (stmt_escape_type == ESCAPE_TO_PURE_CONST) mem_ref_stats->num_pure_const_call_sites++; } else if (stmt_escape_type == ESCAPE_TO_ASM) mem_ref_stats->num_asm_sites++; /* Mark all the variables whose address are taken by the statement. */ addr_taken = gimple_addresses_taken (stmt); if (addr_taken) bitmap_ior_into (gimple_addressable_vars (cfun), addr_taken); /* If we have a call or an assignment, see if the lhs contains a local decl that requires not to be a gimple register. */ if (gimple_code (stmt) == GIMPLE_ASSIGN || gimple_code (stmt) == GIMPLE_CALL) { tree lhs = gimple_get_lhs (stmt); /* A plain decl does not need it set. */ if (lhs && handled_component_p (lhs)) { tree var = get_base_address (lhs); if (DECL_P (var) /* We are not going to mess with RESULT_DECL anyway. */ && TREE_CODE (var) != RESULT_DECL && is_gimple_reg_type (TREE_TYPE (var))) bitmap_set_bit (gimple_addressable_vars (cfun), DECL_UID (var)); } } /* Process each operand use. For pointers, determine whether they are dereferenced by the statement, or whether their value escapes, etc. */ FOR_EACH_PHI_OR_STMT_USE (use_p, stmt, iter, SSA_OP_USE) { tree op, var; var_ann_t v_ann; struct ptr_info_def *pi; unsigned num_uses, num_loads, num_stores; op = USE_FROM_PTR (use_p); /* If STMT is a PHI node, OP may be an ADDR_EXPR. If so, add it to the set of addressable variables. */ if (TREE_CODE (op) == ADDR_EXPR) { bitmap addressable_vars = gimple_addressable_vars (cfun); gcc_assert (gimple_code (stmt) == GIMPLE_PHI); gcc_assert (addressable_vars); /* PHI nodes don't have annotations for pinning the set of addresses taken, so we collect them here. FIXME, should we allow PHI nodes to have annotations so that they can be treated like regular statements? Currently, they are treated as second-class statements. */ add_to_addressable_set (TREE_OPERAND (op, 0), &addressable_vars); continue; } /* Ignore constants (they may occur in PHI node arguments). */ if (TREE_CODE (op) != SSA_NAME) continue; var = SSA_NAME_VAR (op); v_ann = var_ann (var); /* The base variable of an SSA name must be a GIMPLE register, and thus it cannot be aliased. */ gcc_assert (!may_be_aliased (var)); /* We are only interested in pointers. */ if (!POINTER_TYPE_P (TREE_TYPE (op))) continue; pi = get_ptr_info (op); /* Add OP to AI->PROCESSED_PTRS, if it's not there already. */ if (!TEST_BIT (ai->ssa_names_visited, SSA_NAME_VERSION (op))) { SET_BIT (ai->ssa_names_visited, SSA_NAME_VERSION (op)); VEC_safe_push (tree, heap, ai->processed_ptrs, op); } /* If STMT is a PHI node, then it will not have pointer dereferences and it will not be an escape point. */ if (gimple_code (stmt) == GIMPLE_PHI) continue; /* Determine whether OP is a dereferenced pointer, and if STMT is an escape point, whether OP escapes. */ count_uses_and_derefs (op, stmt, &num_uses, &num_loads, &num_stores); /* For directly dereferenced pointers we can apply TBAA-pruning to their points-to set. We may not count the implicit dereferences &PTR->FLD here. */ if (num_loads + num_stores > 0) pi->is_dereferenced = 1; /* Handle a corner case involving address expressions of the form '&PTR->FLD'. The problem with these expressions is that they do not represent a dereference of PTR. However, if some other transformation propagates them into an INDIRECT_REF expression, we end up with '*(&PTR->FLD)' which is folded into 'PTR->FLD'. So, if the original code had no other dereferences of PTR, the aliaser will not create memory tags for it, and when &PTR->FLD gets propagated to INDIRECT_REF expressions, the memory operations will receive no VDEF/VUSE operands. One solution would be to have count_uses_and_derefs consider &PTR->FLD a dereference of PTR. But that is wrong, since it is not really a dereference but an offset calculation. What we do here is to recognize these special ADDR_EXPR nodes. Since these expressions are never GIMPLE values (they are not GIMPLE invariants), they can only appear on the RHS of an assignment and their base address is always an INDIRECT_REF expression. */ if (is_gimple_assign (stmt) && gimple_assign_rhs_code (stmt) == ADDR_EXPR && !is_gimple_val (gimple_assign_rhs1 (stmt))) { /* If the RHS if of the form &PTR->FLD and PTR == OP, then this represents a potential dereference of PTR. */ tree rhs = gimple_assign_rhs1 (stmt); tree base = get_base_address (TREE_OPERAND (rhs, 0)); if (TREE_CODE (base) == INDIRECT_REF && TREE_OPERAND (base, 0) == op) num_loads++; } if (num_loads + num_stores > 0) { /* Mark OP as dereferenced. In a subsequent pass, dereferenced pointers that point to a set of variables will be assigned a name tag to alias all the variables OP points to. */ pi->memory_tag_needed = 1; /* ??? For always executed direct dereferences we can apply TBAA-pruning to their escape set. */ /* Mark OP as being dereferenced. */ pointer_set_insert (ai->dereferenced_ptrs, var); /* Update the frequency estimate for all the dereferences of pointer OP. */ update_mem_sym_stats_from_stmt (op, stmt, num_loads, num_stores); /* Indicate that STMT contains pointer dereferences. */ stmt_dereferences_ptr_p = true; } if (stmt_escape_type != NO_ESCAPE && num_loads + num_stores < num_uses) { /* If STMT is an escape point and STMT contains at least one direct use of OP, then the value of OP escapes and so the pointed-to variables need to be marked call-clobbered. */ pi->value_escapes_p = 1; pi->escape_mask |= stmt_escape_type; /* If the statement makes a function call, assume that pointer OP will be dereferenced in a store operation inside the called function. */ if (is_gimple_call (stmt) || stmt_escape_type == ESCAPE_STORED_IN_GLOBAL) { pointer_set_insert (ai->dereferenced_ptrs, var); pi->memory_tag_needed = 1; } } } if (gimple_code (stmt) == GIMPLE_PHI) return; /* Mark stored variables in STMT as being written to and update the memory reference stats for all memory symbols referenced by STMT. */ if (gimple_references_memory_p (stmt)) { unsigned i; bitmap_iterator bi; mem_ref_stats->num_mem_stmts++; /* Notice that we only update memory reference stats for symbols loaded and stored by the statement if the statement does not contain pointer dereferences and it is not a call/asm site. This is to avoid double accounting problems when creating memory partitions. After computing points-to information, pointer dereference statistics are used to update the reference stats of the pointed-to variables, so here we should only update direct references to symbols. Indirect references are not updated here for two reasons: (1) The first time we compute alias information, the sets LOADED/STORED are empty for pointer dereferences, (2) After partitioning, LOADED/STORED may have references to partitions, not the original pointed-to variables. So, if we always counted LOADED/STORED here and during partitioning, we would count many symbols more than once. This does cause some imprecision when a statement has a combination of direct symbol references and pointer dereferences (e.g., MEMORY_VAR = *PTR) or if a call site has memory symbols in its argument list, but these cases do not occur so frequently as to constitute a serious problem. */ if (!stmt_dereferences_ptr_p && stmt_escape_type != ESCAPE_TO_CALL && stmt_escape_type != ESCAPE_TO_PURE_CONST && stmt_escape_type != ESCAPE_TO_ASM) { if (gimple_stored_syms (stmt)) EXECUTE_IF_SET_IN_BITMAP (gimple_stored_syms (stmt), 0, i, bi) update_mem_sym_stats_from_stmt (referenced_var (i), stmt, 0, 1); if (gimple_loaded_syms (stmt)) EXECUTE_IF_SET_IN_BITMAP (gimple_loaded_syms (stmt), 0, i, bi) update_mem_sym_stats_from_stmt (referenced_var (i), stmt, 1, 0); } } } /* Update various related attributes like escaped addresses, pointer dereferences for loads and stores. This is used when creating name tags and alias sets. */ static void update_alias_info (struct alias_info *ai) { basic_block bb; FOR_EACH_BB (bb) { gimple_stmt_iterator gsi; gimple phi; for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { phi = gsi_stmt (gsi); if (is_gimple_reg (PHI_RESULT (phi))) update_alias_info_1 (phi, ai); } for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) update_alias_info_1 (gsi_stmt (gsi), ai); } } /* Create memory tags for all the dereferenced pointers and build the ADDRESSABLE_VARS and POINTERS arrays used for building the may-alias sets. Based on the address escape and points-to information collected earlier, this pass will also clear the TREE_ADDRESSABLE flag from those variables whose address is not needed anymore. */ static void setup_pointers_and_addressables (struct alias_info *ai) { size_t num_addressable_vars, num_pointers; referenced_var_iterator rvi; tree var; VEC (tree, heap) *varvec = NULL; safe_referenced_var_iterator srvi; /* Size up the arrays ADDRESSABLE_VARS and POINTERS. */ num_addressable_vars = num_pointers = 0; FOR_EACH_REFERENCED_VAR (var, rvi) { if (may_be_aliased (var)) num_addressable_vars++; if (POINTER_TYPE_P (TREE_TYPE (var))) { /* Since we don't keep track of volatile variables, assume that these pointers are used in indirect store operations. */ if (TREE_THIS_VOLATILE (var)) pointer_set_insert (ai->dereferenced_ptrs, var); num_pointers++; } } /* Create ADDRESSABLE_VARS and POINTERS. Note that these arrays are always going to be slightly bigger than we actually need them because some TREE_ADDRESSABLE variables will be marked non-addressable below and only pointers with unique symbol tags are going to be added to POINTERS. */ ai->addressable_vars = XCNEWVEC (struct alias_map_d *, num_addressable_vars); ai->pointers = XCNEWVEC (struct alias_map_d *, num_pointers); ai->num_addressable_vars = 0; ai->num_pointers = 0; FOR_EACH_REFERENCED_VAR_SAFE (var, varvec, srvi) { /* Name memory tags already have flow-sensitive aliasing information, so they need not be processed by compute_flow_insensitive_aliasing. Similarly, symbol memory tags are already accounted for when we process their associated pointer. Structure fields, on the other hand, have to have some of this information processed for them, but it's pointless to mark them non-addressable (since they are fake variables anyway). */ if (MTAG_P (var)) continue; /* Remove the ADDRESSABLE flag from every addressable variable whose address is not needed anymore. This is caused by the propagation of ADDR_EXPR constants into INDIRECT_REF expressions and the removal of dead pointer assignments done by the early scalar cleanup passes. */ if (TREE_ADDRESSABLE (var)) { if (!bitmap_bit_p (gimple_addressable_vars (cfun), DECL_UID (var)) && TREE_CODE (var) != RESULT_DECL && !is_global_var (var)) { bool okay_to_mark = true; /* Since VAR is now a regular GIMPLE register, we will need to rename VAR into SSA afterwards. */ mark_sym_for_renaming (var); /* The address of VAR is not needed, remove the addressable bit, so that it can be optimized as a regular variable. */ if (okay_to_mark) { /* The memory partition holding VAR will no longer contain VAR, and statements referencing it will need to be updated. */ if (memory_partition (var)) mark_sym_for_renaming (memory_partition (var)); mark_non_addressable (var); } } } /* Global variables and addressable locals may be aliased. Create an entry in ADDRESSABLE_VARS for VAR. */ if (may_be_aliased (var)) { create_alias_map_for (var, ai); mark_sym_for_renaming (var); } /* Add pointer variables that have been dereferenced to the POINTERS array and create a symbol memory tag for them. */ if (POINTER_TYPE_P (TREE_TYPE (var))) { if (pointer_set_contains (ai->dereferenced_ptrs, var)) { tree tag, old_tag; var_ann_t t_ann; /* If pointer VAR still doesn't have a memory tag associated with it, create it now or re-use an existing one. */ tag = get_smt_for (var, ai); t_ann = var_ann (tag); /* The symbol tag will need to be renamed into SSA afterwards. Note that we cannot do this inside get_smt_for because aliasing may run multiple times and we only create symbol tags the first time. */ mark_sym_for_renaming (tag); /* Similarly, if pointer VAR used to have another type tag, we will need to process it in the renamer to remove the stale virtual operands. */ old_tag = symbol_mem_tag (var); if (old_tag) mark_sym_for_renaming (old_tag); /* Associate the tag with pointer VAR. */ set_symbol_mem_tag (var, tag); } else { /* The pointer has not been dereferenced. If it had a symbol memory tag, remove it and mark the old tag for renaming to remove it out of the IL. */ tree tag = symbol_mem_tag (var); if (tag) { mark_sym_for_renaming (tag); set_symbol_mem_tag (var, NULL_TREE); } } } } VEC_free (tree, heap, varvec); } /* Determine whether to use .GLOBAL_VAR to model call clobbering semantics. If the function makes no references to global variables and contains at least one call to a non-pure function, then we need to mark the side-effects of the call using .GLOBAL_VAR to represent all possible global memory referenced by the callee. */ static void maybe_create_global_var (void) { /* No need to create it, if we have one already. */ if (gimple_global_var (cfun) == NULL_TREE) { struct mem_ref_stats_d *stats = gimple_mem_ref_stats (cfun); /* Create .GLOBAL_VAR if there are no call-clobbered variables and the program contains a mixture of pure/const and regular function calls. This is to avoid the problem described in PR 20115: int X; int func_pure (void) { return X; } int func_non_pure (int a) { X += a; } int foo () { int a = func_pure (); func_non_pure (a); a = func_pure (); return a; } Since foo() has no call-clobbered variables, there is no relationship between the calls to func_pure and func_non_pure. Since func_pure has no side-effects, value numbering optimizations elide the second call to func_pure. So, if we have some pure/const and some regular calls in the program we create .GLOBAL_VAR to avoid missing these relations. */ if (bitmap_empty_p (gimple_call_clobbered_vars (cfun)) && stats->num_call_sites > 0 && stats->num_pure_const_call_sites > 0 && stats->num_call_sites > stats->num_pure_const_call_sites) create_global_var (); } } /* Return TRUE if pointer PTR may point to variable VAR. MEM_ALIAS_SET is the alias set for the memory location pointed-to by PTR This is needed because when checking for type conflicts we are interested in the alias set of the memory location pointed-to by PTR. The alias set of PTR itself is irrelevant. VAR_ALIAS_SET is the alias set for VAR. */ bool may_alias_p (tree ptr, alias_set_type mem_alias_set, tree var, alias_set_type var_alias_set, bool alias_set_only) { tree mem; alias_stats.alias_queries++; alias_stats.simple_queries++; /* By convention, a variable cannot alias itself. */ mem = symbol_mem_tag (ptr); if (mem == var) { alias_stats.alias_noalias++; alias_stats.simple_resolved++; return false; } /* If -fargument-noalias-global is > 2, pointer arguments may not point to anything else. */ if (flag_argument_noalias > 2 && TREE_CODE (ptr) == PARM_DECL) { alias_stats.alias_noalias++; alias_stats.simple_resolved++; return false; } /* If -fargument-noalias-global is > 1, pointer arguments may not point to global variables. */ if (flag_argument_noalias > 1 && is_global_var (var) && TREE_CODE (ptr) == PARM_DECL) { alias_stats.alias_noalias++; alias_stats.simple_resolved++; return false; } /* If the pointed to memory has alias set zero, or the pointer is ref-all, or the pointer decl is marked that no TBAA is to be applied, the MEM can alias VAR. */ if (mem_alias_set == 0 || DECL_POINTER_ALIAS_SET (ptr) == 0 || TYPE_REF_CAN_ALIAS_ALL (TREE_TYPE (ptr)) || DECL_NO_TBAA_P (ptr)) { alias_stats.alias_mayalias++; alias_stats.simple_resolved++; return true; } gcc_assert (TREE_CODE (mem) == SYMBOL_MEMORY_TAG); alias_stats.tbaa_queries++; /* If the alias sets don't conflict then MEM cannot alias VAR. */ if (mem_alias_set != var_alias_set && !alias_set_subset_of (mem_alias_set, var_alias_set)) { alias_stats.alias_noalias++; alias_stats.tbaa_resolved++; return false; } /* If VAR is a record or union type, PTR cannot point into VAR unless there is some explicit address operation in the program that can reference a field of the type pointed-to by PTR. This also assumes that the types of both VAR and PTR are contained within the compilation unit, and that there is no fancy addressing arithmetic associated with any of the types involved. */ if (mem_alias_set != 0 && var_alias_set != 0) { tree ptr_type = TREE_TYPE (ptr); tree var_type = TREE_TYPE (var); /* The star count is -1 if the type at the end of the pointer_to chain is not a record or union type. */ if (!alias_set_only && 0 /* FIXME tuples ipa_type_escape_star_count_of_interesting_type (var_type) >= 0*/) { int ptr_star_count = 0; /* ipa_type_escape_star_count_of_interesting_type is a little too restrictive for the pointer type, need to allow pointers to primitive types as long as those types cannot be pointers to everything. */ while (POINTER_TYPE_P (ptr_type)) { /* Strip the *s off. */ ptr_type = TREE_TYPE (ptr_type); ptr_star_count++; } /* There does not appear to be a better test to see if the pointer type was one of the pointer to everything types. */ if (ptr_star_count > 0) { alias_stats.structnoaddress_queries++; if (ipa_type_escape_field_does_not_clobber_p (var_type, TREE_TYPE (ptr))) { alias_stats.structnoaddress_resolved++; alias_stats.alias_noalias++; return false; } } else if (ptr_star_count == 0) { /* If PTR_TYPE was not really a pointer to type, it cannot alias. */ alias_stats.structnoaddress_queries++; alias_stats.structnoaddress_resolved++; alias_stats.alias_noalias++; return false; } } } alias_stats.alias_mayalias++; return true; } /* Return true, if PTR may point to a global variable. */ bool may_point_to_global_var (tree ptr) { struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr); /* If we do not have points-to information for this variable, we have to punt. */ if (!pi || !pi->name_mem_tag) return true; /* The name memory tag is marked as global variable if the points-to set contains a global variable. */ return is_global_var (pi->name_mem_tag); } /* Add ALIAS to the set of variables that may alias VAR. */ static void add_may_alias (tree var, tree alias) { /* Don't allow self-referential aliases. */ gcc_assert (var != alias); /* ALIAS must be addressable if it's being added to an alias set. */ #if 1 TREE_ADDRESSABLE (alias) = 1; #else gcc_assert (may_be_aliased (alias)); #endif /* VAR must be a symbol or a name tag. */ gcc_assert (TREE_CODE (var) == SYMBOL_MEMORY_TAG || TREE_CODE (var) == NAME_MEMORY_TAG); if (MTAG_ALIASES (var) == NULL) MTAG_ALIASES (var) = BITMAP_ALLOC (&alias_bitmap_obstack); bitmap_set_bit (MTAG_ALIASES (var), DECL_UID (alias)); } /* Mark pointer PTR as pointing to an arbitrary memory location. */ static void set_pt_anything (tree ptr) { struct ptr_info_def *pi = get_ptr_info (ptr); pi->pt_anything = 1; /* Anything includes global memory. */ pi->pt_global_mem = 1; pi->pt_vars = NULL; /* The pointer used to have a name tag, but we now found it pointing to an arbitrary location. The name tag needs to be renamed and disassociated from PTR. */ if (pi->name_mem_tag) { mark_sym_for_renaming (pi->name_mem_tag); pi->name_mem_tag = NULL_TREE; } } /* Return true if STMT is an "escape" site from the current function. Escape sites those statements which might expose the address of a variable outside the current function. STMT is an escape site iff: 1- STMT is a function call, or 2- STMT is an __asm__ expression, or 3- STMT is an assignment to a non-local variable, or 4- STMT is a return statement. Return the type of escape site found, if we found one, or NO_ESCAPE if none. */ enum escape_type is_escape_site (gimple stmt) { if (is_gimple_call (stmt)) { if (gimple_call_flags (stmt) & (ECF_PURE | ECF_CONST)) return ESCAPE_TO_PURE_CONST; return ESCAPE_TO_CALL; } else if (gimple_code (stmt) == GIMPLE_ASM) return ESCAPE_TO_ASM; else if (is_gimple_assign (stmt)) { tree lhs = gimple_assign_lhs (stmt); /* Get to the base of _REF nodes. */ if (TREE_CODE (lhs) != SSA_NAME) lhs = get_base_address (lhs); /* If we couldn't recognize the LHS of the assignment, assume that it is a non-local store. */ if (lhs == NULL_TREE) return ESCAPE_UNKNOWN; if (gimple_assign_cast_p (stmt)) { tree from = TREE_TYPE (gimple_assign_rhs1 (stmt)); tree to = TREE_TYPE (lhs); /* If the RHS is a conversion between a pointer and an integer, the pointer escapes since we can't track the integer. */ if (POINTER_TYPE_P (from) && !POINTER_TYPE_P (to)) return ESCAPE_BAD_CAST; } /* If the LHS is an SSA name, it can't possibly represent a non-local memory store. */ if (TREE_CODE (lhs) == SSA_NAME) return NO_ESCAPE; /* If the LHS is a non-global decl, it isn't a non-local memory store. If the LHS escapes, the RHS escape is dealt with in the PTA solver. */ if (DECL_P (lhs) && !is_global_var (lhs)) return NO_ESCAPE; /* FIXME: LHS is not an SSA_NAME. Even if it's an assignment to a local variables we cannot be sure if it will escape, because we don't have information about objects not in SSA form. Need to implement something along the lines of J.-D. Choi, M. Gupta, M. J. Serrano, V. C. Sreedhar, and S. P. Midkiff, ``Escape analysis for java,'' in Proceedings of the Conference on Object-Oriented Programming Systems, Languages, and Applications (OOPSLA), pp. 1-19, 1999. */ return ESCAPE_STORED_IN_GLOBAL; } else if (gimple_code (stmt) == GIMPLE_RETURN) return ESCAPE_TO_RETURN; return NO_ESCAPE; } /* Create a new memory tag of type TYPE. Does NOT push it into the current binding. */ tree create_tag_raw (enum tree_code code, tree type, const char *prefix) { tree tmp_var; tmp_var = build_decl (code, create_tmp_var_name (prefix), type); /* Memory tags are always writable and non-static. */ TREE_READONLY (tmp_var) = 0; TREE_STATIC (tmp_var) = 0; /* It doesn't start out global. */ MTAG_GLOBAL (tmp_var) = 0; TREE_USED (tmp_var) = 1; return tmp_var; } /* Create a new memory tag of type TYPE. If IS_TYPE_TAG is true, the tag is considered to represent all the pointers whose pointed-to types are in the same alias set class. Otherwise, the tag represents a single SSA_NAME pointer variable. */ static tree create_memory_tag (tree type, bool is_type_tag) { tree tag = create_tag_raw (is_type_tag ? SYMBOL_MEMORY_TAG : NAME_MEMORY_TAG, type, (is_type_tag) ? "SMT" : "NMT"); /* By default, memory tags are local variables. Alias analysis will determine whether they should be considered globals. */ DECL_CONTEXT (tag) = current_function_decl; /* Memory tags are by definition addressable. */ TREE_ADDRESSABLE (tag) = 1; set_symbol_mem_tag (tag, NULL_TREE); /* Add the tag to the symbol table. */ add_referenced_var (tag); return tag; } /* Create a name memory tag to represent a specific SSA_NAME pointer P_i. This is used if P_i has been found to point to a specific set of variables or to a non-aliased memory location like the address returned by malloc functions. */ static tree get_nmt_for (tree ptr) { struct ptr_info_def *pi = get_ptr_info (ptr); tree tag = pi->name_mem_tag; if (tag == NULL_TREE) tag = create_memory_tag (TREE_TYPE (TREE_TYPE (ptr)), false); return tag; } /* Return the symbol memory tag associated to pointer PTR. A memory tag is an artificial variable that represents the memory location pointed-to by PTR. It is used to model the effects of pointer de-references on addressable variables. AI points to the data gathered during alias analysis. This function populates the array AI->POINTERS. */ static tree get_smt_for (tree ptr, struct alias_info *ai) { size_t i; tree tag; tree tag_type = TREE_TYPE (TREE_TYPE (ptr)); alias_set_type tag_set; /* Get the alias set to be used for the pointed-to memory. If that differs from what we would get from looking at the type adjust the tag_type to void to make sure we get a proper alias set from just looking at the SMT we create. */ tag_set = get_alias_set (tag_type); if (TYPE_REF_CAN_ALIAS_ALL (TREE_TYPE (ptr)) /* This is overly conservative but we do not want to assign restrict alias sets here (which if they are not assigned are -2 but still "known"). */ || DECL_POINTER_ALIAS_SET_KNOWN_P (ptr)) { tag_set = 0; tag_type = void_type_node; } /* To avoid creating unnecessary memory tags, only create one memory tag per alias set class. Note that it may be tempting to group memory tags based on conflicting alias sets instead of equivalence. That would be wrong because alias sets are not necessarily transitive (as demonstrated by the libstdc++ test 23_containers/vector/cons/4.cc). Given three alias sets A, B, C such that conflicts (A, B) == true and conflicts (A, C) == true, it does not necessarily follow that conflicts (B, C) == true. */ for (i = 0, tag = NULL_TREE; i < ai->num_pointers; i++) { struct alias_map_d *curr = ai->pointers[i]; tree curr_tag = symbol_mem_tag (curr->var); if (tag_set == curr->set) { tag = curr_tag; break; } } /* If VAR cannot alias with any of the existing memory tags, create a new tag for PTR and add it to the POINTERS array. */ if (tag == NULL_TREE) { struct alias_map_d *alias_map; /* If PTR did not have a symbol tag already, create a new SMT.* artificial variable representing the memory location pointed-to by PTR. */ tag = symbol_mem_tag (ptr); if (tag == NULL_TREE || tag_set != get_alias_set (tag)) tag = create_memory_tag (tag_type, true); /* Add PTR to the POINTERS array. Note that we are not interested in PTR's alias set. Instead, we cache the alias set for the memory that PTR points to. */ alias_map = XCNEW (struct alias_map_d); alias_map->var = ptr; alias_map->set = tag_set; ai->pointers[ai->num_pointers++] = alias_map; } /* If the pointed-to type is volatile, so is the tag. */ TREE_THIS_VOLATILE (tag) |= TREE_THIS_VOLATILE (tag_type); /* Make sure that the symbol tag has the same alias set as the pointed-to type or at least accesses through the pointer will alias that set. The latter can happen after the vectorizer created pointers of vector type. */ gcc_assert (tag_set == get_alias_set (tag) || alias_set_subset_of (tag_set, get_alias_set (tag))); return tag; } /* Create GLOBAL_VAR, an artificial global variable to act as a representative of all the variables that may be clobbered by function calls. */ static void create_global_var (void) { tree global_var = build_decl (VAR_DECL, get_identifier (".GLOBAL_VAR"), void_type_node); DECL_ARTIFICIAL (global_var) = 1; TREE_READONLY (global_var) = 0; DECL_EXTERNAL (global_var) = 1; TREE_STATIC (global_var) = 1; TREE_USED (global_var) = 1; DECL_CONTEXT (global_var) = NULL_TREE; TREE_THIS_VOLATILE (global_var) = 0; TREE_ADDRESSABLE (global_var) = 0; create_var_ann (global_var); mark_call_clobbered (global_var, ESCAPE_UNKNOWN); add_referenced_var (global_var); mark_sym_for_renaming (global_var); cfun->gimple_df->global_var = global_var; } /* Dump alias statistics on FILE. */ static void dump_alias_stats (FILE *file) { const char *funcname = lang_hooks.decl_printable_name (current_function_decl, 2); fprintf (file, "\nAlias statistics for %s\n\n", funcname); fprintf (file, "Total alias queries:\t%u\n", alias_stats.alias_queries); fprintf (file, "Total alias mayalias results:\t%u\n", alias_stats.alias_mayalias); fprintf (file, "Total alias noalias results:\t%u\n", alias_stats.alias_noalias); fprintf (file, "Total simple queries:\t%u\n", alias_stats.simple_queries); fprintf (file, "Total simple resolved:\t%u\n", alias_stats.simple_resolved); fprintf (file, "Total TBAA queries:\t%u\n", alias_stats.tbaa_queries); fprintf (file, "Total TBAA resolved:\t%u\n", alias_stats.tbaa_resolved); fprintf (file, "Total non-addressable structure type queries:\t%u\n", alias_stats.structnoaddress_queries); fprintf (file, "Total non-addressable structure type resolved:\t%u\n", alias_stats.structnoaddress_resolved); } /* Dump alias information on FILE. */ void dump_alias_info (FILE *file) { size_t i; const char *funcname = lang_hooks.decl_printable_name (current_function_decl, 2); referenced_var_iterator rvi; tree var; fprintf (file, "\nAlias information for %s\n\n", funcname); dump_memory_partitions (file); fprintf (file, "\nFlow-insensitive alias information for %s\n\n", funcname); fprintf (file, "Aliased symbols\n\n"); FOR_EACH_REFERENCED_VAR (var, rvi) { if (may_be_aliased (var)) dump_variable (file, var); } fprintf (file, "\nDereferenced pointers\n\n"); FOR_EACH_REFERENCED_VAR (var, rvi) if (symbol_mem_tag (var)) dump_variable (file, var); fprintf (file, "\nSymbol memory tags\n\n"); FOR_EACH_REFERENCED_VAR (var, rvi) { if (TREE_CODE (var) == SYMBOL_MEMORY_TAG) dump_variable (file, var); } fprintf (file, "\n\nFlow-sensitive alias information for %s\n\n", funcname); fprintf (file, "SSA_NAME pointers\n\n"); for (i = 1; i < num_ssa_names; i++) { tree ptr = ssa_name (i); struct ptr_info_def *pi; if (ptr == NULL_TREE) continue; pi = SSA_NAME_PTR_INFO (ptr); if (!SSA_NAME_IN_FREE_LIST (ptr) && pi && pi->name_mem_tag) dump_points_to_info_for (file, ptr); } fprintf (file, "\nName memory tags\n\n"); FOR_EACH_REFERENCED_VAR (var, rvi) { if (TREE_CODE (var) == NAME_MEMORY_TAG) dump_variable (file, var); } fprintf (file, "\n"); } /* Dump alias information on stderr. */ void debug_alias_info (void) { dump_alias_info (stderr); } /* Return the alias information associated with pointer T. It creates a new instance if none existed. */ struct ptr_info_def * get_ptr_info (tree t) { struct ptr_info_def *pi; gcc_assert (POINTER_TYPE_P (TREE_TYPE (t))); pi = SSA_NAME_PTR_INFO (t); if (pi == NULL) { pi = GGC_CNEW (struct ptr_info_def); SSA_NAME_PTR_INFO (t) = pi; } return pi; } /* Dump points-to information for SSA_NAME PTR into FILE. */ void dump_points_to_info_for (FILE *file, tree ptr) { struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr); print_generic_expr (file, ptr, dump_flags); if (pi) { if (pi->name_mem_tag) { fprintf (file, ", name memory tag: "); print_generic_expr (file, pi->name_mem_tag, dump_flags); } if (pi->is_dereferenced) fprintf (file, ", is dereferenced"); else if (pi->memory_tag_needed) fprintf (file, ", is dereferenced in call"); if (pi->value_escapes_p) fprintf (file, ", its value escapes"); if (pi->pt_anything) fprintf (file, ", points-to anything"); if (pi->pt_null) fprintf (file, ", points-to NULL"); if (pi->pt_vars) { fprintf (file, ", points-to vars: "); dump_decl_set (file, pi->pt_vars); } } fprintf (file, "\n"); } /* Dump points-to information for VAR into stderr. */ void debug_points_to_info_for (tree var) { dump_points_to_info_for (stderr, var); } /* Dump points-to information into FILE. NOTE: This function is slow, as it needs to traverse the whole CFG looking for pointer SSA_NAMEs. */ void dump_points_to_info (FILE *file ATTRIBUTE_UNUSED) { basic_block bb; gimple_stmt_iterator si; ssa_op_iter iter; const char *fname = lang_hooks.decl_printable_name (current_function_decl, 2); referenced_var_iterator rvi; tree var; fprintf (file, "\n\nPointed-to sets for pointers in %s\n\n", fname); /* First dump points-to information for the default definitions of pointer variables. This is necessary because default definitions are not part of the code. */ FOR_EACH_REFERENCED_VAR (var, rvi) { if (POINTER_TYPE_P (TREE_TYPE (var))) { tree def = gimple_default_def (cfun, var); if (def) dump_points_to_info_for (file, def); } } /* Dump points-to information for every pointer defined in the program. */ FOR_EACH_BB (bb) { for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si)) { gimple phi = gsi_stmt (si); tree ptr = PHI_RESULT (phi); if (POINTER_TYPE_P (TREE_TYPE (ptr))) dump_points_to_info_for (file, ptr); } for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si)) { gimple stmt = gsi_stmt (si); tree def; FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF) if (TREE_CODE (def) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (def))) dump_points_to_info_for (file, def); } } fprintf (file, "\n"); } /* Dump points-to info pointed to by PTO into STDERR. */ void debug_points_to_info (void) { dump_points_to_info (stderr); } /* Dump to FILE the list of variables that may be aliasing VAR. */ void dump_may_aliases_for (FILE *file, tree var) { bitmap aliases; aliases = MTAG_ALIASES (var); if (aliases) { bitmap_iterator bi; unsigned int i; tree al; fprintf (file, "{ "); EXECUTE_IF_SET_IN_BITMAP (aliases, 0, i, bi) { al = referenced_var (i); print_generic_expr (file, al, dump_flags); fprintf (file, " "); } fprintf (file, "}"); } } /* Dump to stderr the list of variables that may be aliasing VAR. */ void debug_may_aliases_for (tree var) { dump_may_aliases_for (stderr, var); } /* Return true if VAR may be aliased. */ bool may_be_aliased (tree var) { /* Obviously. */ if (TREE_ADDRESSABLE (var)) return true; /* Globally visible variables can have their addresses taken by other translation units. */ if (MTAG_P (var) && MTAG_GLOBAL (var)) return true; else if (!MTAG_P (var) && (DECL_EXTERNAL (var) || TREE_PUBLIC (var))) return true; /* Automatic variables can't have their addresses escape any other way. This must be after the check for global variables, as extern declarations do not have TREE_STATIC set. */ if (!TREE_STATIC (var)) return false; return false; } /* The following is based on code in add_stmt_operand to ensure that the same defs/uses/vdefs/vuses will be found after replacing a reference to var (or ARRAY_REF to var) with an INDIRECT_REF to ptr whose value is the address of var. Return a memtag for the ptr, after adding the proper may_aliases to it (which are the aliases of var, if it has any, or var itself). */ static tree add_may_alias_for_new_tag (tree tag, tree var) { bitmap aliases = NULL; if (MTAG_P (var)) aliases = may_aliases (var); /* Case 1: |aliases| == 1 */ if (aliases && bitmap_single_bit_set_p (aliases)) { tree ali = referenced_var (bitmap_first_set_bit (aliases)); if (TREE_CODE (ali) == SYMBOL_MEMORY_TAG) return ali; } /* Case 2: |aliases| == 0 */ if (aliases == NULL) add_may_alias (tag, var); else { /* Case 3: |aliases| > 1 */ union_alias_set_into (tag, aliases); } return tag; } /* Create a new symbol tag for PTR. Construct the may-alias list of this type tag so that it has the aliasing of VAR according to the location accessed by EXPR. Note, the set of aliases represented by the new symbol tag are not marked for renaming. */ void new_type_alias (tree ptr, tree var, tree expr) { tree tag_type = TREE_TYPE (TREE_TYPE (ptr)); tree tag; tree ali = NULL_TREE; HOST_WIDE_INT offset, size, maxsize; tree ref; gcc_assert (symbol_mem_tag (ptr) == NULL_TREE); gcc_assert (!MTAG_P (var)); ref = get_ref_base_and_extent (expr, &offset, &size, &maxsize); gcc_assert (ref); tag = create_memory_tag (tag_type, true); set_symbol_mem_tag (ptr, tag); ali = add_may_alias_for_new_tag (tag, var); set_symbol_mem_tag (ptr, ali); MTAG_GLOBAL (tag) = is_global_var (var); } /* Reset the call_clobbered flags on our referenced vars. In theory, this only needs to be done for globals. */ static unsigned int reset_cc_flags (void) { tree var; referenced_var_iterator rvi; FOR_EACH_REFERENCED_VAR (var, rvi) var_ann (var)->call_clobbered = false; return 0; } struct gimple_opt_pass pass_reset_cc_flags = { { GIMPLE_PASS, NULL, /* name */ NULL, /* gate */ reset_cc_flags, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ 0, /* tv_id */ PROP_referenced_vars |PROP_cfg, /* properties_required */ 0, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ 0 /* todo_flags_finish */ } }; /* A dummy pass to cause aliases to be computed via TODO_rebuild_alias. */ struct gimple_opt_pass pass_build_alias = { { GIMPLE_PASS, "alias", /* name */ NULL, /* gate */ NULL, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ 0, /* tv_id */ PROP_cfg | PROP_ssa, /* properties_required */ PROP_alias, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_rebuild_alias | TODO_dump_func /* todo_flags_finish */ } };