/* Alias analysis for trees. Copyright (C) 2004, 2005 Free Software Foundation, Inc. Contributed by Diego Novillo <dnovillo@redhat.com> 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 2, 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 COPYING. If not, write to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #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 "tree-gimple.h" #include "tree-flow.h" #include "tree-inline.h" #include "tree-pass.h" #include "convert.h" #include "params.h" /* 'true' after aliases have been computed (see compute_may_aliases). */ bool aliases_computed_p; /* Structure to map a variable to its alias set and keep track of the virtual operands that will be needed to represent it. */ struct alias_map_d { /* Variable and its alias set. */ tree var; HOST_WIDE_INT set; /* Total number of virtual operands that will be needed to represent all the aliases of VAR. */ long total_alias_vops; /* Nonzero if the aliases for this memory tag have been grouped already. Used in group_aliases. */ unsigned int grouped_p : 1; /* Set of variables aliased with VAR. This is the exact same information contained in VAR_ANN (VAR)->MAY_ALIASES, but in bitmap form to speed up alias grouping. */ sbitmap may_aliases; }; /* 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. */ varray_type processed_ptrs; /* Variables whose address is still needed. */ bitmap addresses_needed; /* 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; /* Number of function calls found in the program. */ size_t num_calls_found; /* Number of const/pure function calls found in the program. */ size_t num_pure_const_calls_found; /* Array of counters to keep track of how many times each pointer has been dereferenced in the program. This is used by the alias grouping heuristic in compute_flow_insensitive_aliasing. */ varray_type num_references; /* Total number of virtual operands that will be needed to represent all the aliases of all the pointers found in the program. */ long total_alias_vops; /* Variables that have been written to. */ bitmap written_vars; /* Pointers that have been used in an indirect store operation. */ bitmap dereferenced_ptrs_store; /* Pointers that have been used in an indirect load operation. */ bitmap dereferenced_ptrs_load; }; /* 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; }; /* Local variables. */ static struct alias_stats_d alias_stats; /* Local functions. */ static void compute_flow_insensitive_aliasing (struct alias_info *); static void dump_alias_stats (FILE *); static bool may_alias_p (tree, HOST_WIDE_INT, tree, HOST_WIDE_INT); static tree create_memory_tag (tree type, bool is_type_tag); static tree get_tmt_for (tree, struct alias_info *); static tree get_nmt_for (tree); static void add_may_alias (tree, tree); static void replace_may_alias (tree, size_t, tree); static struct alias_info *init_alias_info (void); static void delete_alias_info (struct alias_info *); static void compute_points_to_and_addr_escape (struct alias_info *); static void compute_flow_sensitive_aliasing (struct alias_info *); static void setup_pointers_and_addressables (struct alias_info *); static bool collect_points_to_info_r (tree, tree, void *); static bool is_escape_site (tree, struct alias_info *); static void add_pointed_to_var (struct alias_info *, tree, tree); static void create_global_var (void); static void collect_points_to_info_for (struct alias_info *, tree); static void maybe_create_global_var (struct alias_info *ai); static void group_aliases (struct alias_info *); static void set_pt_anything (tree ptr); static void set_pt_malloc (tree ptr); /* Global declarations. */ /* Call clobbered variables in the function. If bit I is set, then REFERENCED_VARS (I) is call-clobbered. */ bitmap call_clobbered_vars; /* Addressable variables in the function. If bit I is set, then REFERENCED_VARS (I) has had its address taken. Note that CALL_CLOBBERED_VARS and ADDRESSABLE_VARS are not related. An addressable variable is not necessarily call-clobbered (e.g., a local addressable whose address does not escape) and not all call-clobbered variables are addressable (e.g., a local static variable). */ bitmap addressable_vars; /* When the program has too many call-clobbered variables and call-sites, this variable is used to represent the clobbering effects of function calls. In these cases, all the call clobbered variables in the program are forced to alias this variable. This reduces compile times by not having to keep track of too many V_MAY_DEF expressions at call sites. */ tree global_var; /* 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 "type memory tag" (TMT). 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 type 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 type memory tag and every addressable variable found in the program. Given a type memory tag TMT and an addressable variable V. If the alias sets of TMT and V conflict (as computed by may_alias_p), then V is marked as an alias tag and added to the alias set of TMT. 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 type 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 <p_4(1), p_6(2)>; # a_7 = V_MAY_DEF <a_3>; # b_8 = V_MAY_DEF <b_5>; *p_1 = 3; # a_9 = V_MAY_DEF <a_7> # VUSE <b_8> a_9 = b_8 + 2; # VUSE <a_9>; # VUSE <b_8>; 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}), alias sets are grouped to avoid severe compile-time slow downs and memory consumption. See group_aliases. */ static void compute_may_aliases (void) { struct alias_info *ai; 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_and_addr_escape (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 flow-sensitive, points-to based aliasing for all the name memory tags. Note that this pass needs to be done before flow insensitive analysis because it uses the points-to information gathered before to mark call-clobbered type tags. */ compute_flow_sensitive_aliasing (ai); /* Compute type-based flow-insensitive aliasing for all the type memory tags. */ compute_flow_insensitive_aliasing (ai); /* If the program has too many call-clobbered variables and/or function calls, create .GLOBAL_VAR and use it to model call-clobbering semantics at call sites. This reduces the number of virtual operands considerably, improving compile times at the expense of lost aliasing precision. */ maybe_create_global_var (ai); /* Debugging dumps. */ if (dump_file) { dump_referenced_vars (dump_file); if (dump_flags & TDF_STATS) dump_alias_stats (dump_file); dump_points_to_info (dump_file); dump_alias_info (dump_file); } /* Deallocate memory used by aliasing data structures. */ delete_alias_info (ai); } struct tree_opt_pass pass_may_alias = { "alias", /* name */ NULL, /* gate */ compute_may_aliases, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ TV_TREE_MAY_ALIAS, /* tv_id */ PROP_cfg | PROP_ssa, /* properties_required */ PROP_alias, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_rename_vars | TODO_ggc_collect | TODO_verify_ssa | TODO_verify_stmts, /* todo_flags_finish */ 0 /* letter */ }; /* Data structure used to count the number of dereferences to PTR inside an expression. */ struct count_ptr_d { tree ptr; unsigned count; }; /* 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 ATTRIBUTE_UNUSED, void *data) { struct count_ptr_d *count_p = (struct count_ptr_d *) data; if (INDIRECT_REF_P (*tp) && TREE_OPERAND (*tp, 0) == count_p->ptr) count_p->count++; return NULL_TREE; } /* Count the number of direct and indirect uses for pointer PTR in statement STMT. The two counts are stored in *NUM_USES_P and *NUM_DEREFS_P respectively. *IS_STORE_P is set to 'true' if at least one of those dereferences is a store operation. */ static void count_uses_and_derefs (tree ptr, tree stmt, unsigned *num_uses_p, unsigned *num_derefs_p, bool *is_store) { ssa_op_iter i; tree use; *num_uses_p = 0; *num_derefs_p = 0; *is_store = false; /* 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 (TREE_CODE (stmt) == MODIFY_EXPR || (TREE_CODE (stmt) == RETURN_EXPR && TREE_CODE (TREE_OPERAND (stmt, 0)) == MODIFY_EXPR) || TREE_CODE (stmt) == ASM_EXPR || TREE_CODE (stmt) == CALL_EXPR) { tree lhs, rhs; if (TREE_CODE (stmt) == MODIFY_EXPR) { lhs = TREE_OPERAND (stmt, 0); rhs = TREE_OPERAND (stmt, 1); } else if (TREE_CODE (stmt) == RETURN_EXPR) { tree e = TREE_OPERAND (stmt, 0); lhs = TREE_OPERAND (e, 0); rhs = TREE_OPERAND (e, 1); } else if (TREE_CODE (stmt) == ASM_EXPR) { lhs = ASM_OUTPUTS (stmt); rhs = ASM_INPUTS (stmt); } else { lhs = NULL_TREE; rhs = stmt; } if (lhs && (TREE_CODE (lhs) == TREE_LIST || EXPR_P (lhs))) { struct count_ptr_d count; count.ptr = ptr; count.count = 0; walk_tree (&lhs, count_ptr_derefs, &count, NULL); *is_store = true; *num_derefs_p = count.count; } if (rhs && (TREE_CODE (rhs) == TREE_LIST || EXPR_P (rhs))) { struct count_ptr_d count; count.ptr = ptr; count.count = 0; walk_tree (&rhs, count_ptr_derefs, &count, NULL); *num_derefs_p += count.count; } } gcc_assert (*num_uses_p >= *num_derefs_p); } /* Initialize the data structures used for alias analysis. */ static struct alias_info * init_alias_info (void) { struct alias_info *ai; ai = xcalloc (1, sizeof (struct alias_info)); ai->ssa_names_visited = sbitmap_alloc (num_ssa_names); sbitmap_zero (ai->ssa_names_visited); VARRAY_TREE_INIT (ai->processed_ptrs, 50, "processed_ptrs"); ai->addresses_needed = BITMAP_ALLOC (NULL); VARRAY_UINT_INIT (ai->num_references, num_referenced_vars, "num_references"); ai->written_vars = BITMAP_ALLOC (NULL); ai->dereferenced_ptrs_store = BITMAP_ALLOC (NULL); ai->dereferenced_ptrs_load = BITMAP_ALLOC (NULL); /* If aliases have been computed before, clear existing information. */ if (aliases_computed_p) { unsigned i; basic_block bb; /* Make sure that every statement has a valid set of operands. If a statement needs to be scanned for operands while we compute aliases, it may get erroneous operands because all the alias relations are not built at that point. FIXME: This code will become obsolete when operands are not lazily updated. */ FOR_EACH_BB (bb) { block_stmt_iterator si; for (si = bsi_start (bb); !bsi_end_p (si); bsi_next (&si)) get_stmt_operands (bsi_stmt (si)); } /* Similarly, clear the set of addressable variables. In this case, we can just clear the set because addressability is only computed here. */ bitmap_clear (addressable_vars); /* Clear flow-insensitive alias information from each symbol. */ for (i = 0; i < num_referenced_vars; i++) { tree var = referenced_var (i); var_ann_t ann = var_ann (var); ann->is_alias_tag = 0; ann->may_aliases = NULL; /* Since we are about to re-discover call-clobbered variables, clear the call-clobbered flag. Variables that are intrinsically call-clobbered (globals, local statics, etc) will not be marked by the aliasing code, so we can't remove them from CALL_CLOBBERED_VARS. */ if (ann->mem_tag_kind != NOT_A_TAG || !is_global_var (var)) clear_call_clobbered (var); } /* 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_malloc = 0; pi->pt_null = 0; pi->value_escapes_p = 0; pi->is_dereferenced = 0; if (pi->pt_vars) bitmap_clear (pi->pt_vars); } } } /* Next time, we will need to reset alias information. */ aliases_computed_p = 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); ai->processed_ptrs = NULL; BITMAP_FREE (ai->addresses_needed); for (i = 0; i < ai->num_addressable_vars; i++) { sbitmap_free (ai->addressable_vars[i]->may_aliases); free (ai->addressable_vars[i]); } free (ai->addressable_vars); for (i = 0; i < ai->num_pointers; i++) { sbitmap_free (ai->pointers[i]->may_aliases); free (ai->pointers[i]); } free (ai->pointers); ai->num_references = NULL; BITMAP_FREE (ai->written_vars); BITMAP_FREE (ai->dereferenced_ptrs_store); BITMAP_FREE (ai->dereferenced_ptrs_load); free (ai); } /* Walk use-def chains for pointer PTR to determine what variables is PTR pointing to. */ static void collect_points_to_info_for (struct alias_info *ai, tree ptr) { gcc_assert (POINTER_TYPE_P (TREE_TYPE (ptr))); if (!TEST_BIT (ai->ssa_names_visited, SSA_NAME_VERSION (ptr))) { SET_BIT (ai->ssa_names_visited, SSA_NAME_VERSION (ptr)); walk_use_def_chains (ptr, collect_points_to_info_r, ai, true); VARRAY_PUSH_TREE (ai->processed_ptrs, ptr); } } /* Traverse use-def links for all the pointers in the program to collect address escape and points-to information. This is loosely based on the same idea described in R. Hasti and S. Horwitz, ``Using static single assignment form to improve flow-insensitive pointer analysis,'' in SIGPLAN Conference on Programming Language Design and Implementation, pp. 97-105, 1998. */ static void compute_points_to_and_addr_escape (struct alias_info *ai) { basic_block bb; unsigned i; tree op; ssa_op_iter iter; timevar_push (TV_TREE_PTA); FOR_EACH_BB (bb) { bb_ann_t block_ann = bb_ann (bb); block_stmt_iterator si; for (si = bsi_start (bb); !bsi_end_p (si); bsi_next (&si)) { bitmap addr_taken; tree stmt = bsi_stmt (si); bool stmt_escapes_p = is_escape_site (stmt, ai); bitmap_iterator bi; /* Mark all the variables whose address are taken by the statement. Note that this will miss all the addresses taken in PHI nodes (those are discovered while following the use-def chains). */ get_stmt_operands (stmt); addr_taken = addresses_taken (stmt); if (addr_taken) EXECUTE_IF_SET_IN_BITMAP (addr_taken, 0, i, bi) { tree var = referenced_var (i); bitmap_set_bit (ai->addresses_needed, var_ann (var)->uid); if (stmt_escapes_p) mark_call_clobbered (var); } if (stmt_escapes_p) block_ann->has_escape_site = 1; FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_USE) { var_ann_t v_ann = var_ann (SSA_NAME_VAR (op)); struct ptr_info_def *pi; bool is_store; unsigned num_uses, num_derefs; /* If the operand's variable may be aliased, keep track of how many times we've referenced it. This is used for alias grouping in compute_flow_sensitive_aliasing. Note that we don't need to grow AI->NUM_REFERENCES because we are processing regular variables, not memory tags (the array's initial size is set to NUM_REFERENCED_VARS). */ if (may_be_aliased (SSA_NAME_VAR (op))) (VARRAY_UINT (ai->num_references, v_ann->uid))++; if (!POINTER_TYPE_P (TREE_TYPE (op))) continue; collect_points_to_info_for (ai, op); pi = SSA_NAME_PTR_INFO (op); count_uses_and_derefs (op, stmt, &num_uses, &num_derefs, &is_store); if (num_derefs > 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->is_dereferenced = 1; /* Keep track of how many time we've dereferenced each pointer. Again, we don't need to grow AI->NUM_REFERENCES because we're processing existing program variables. */ (VARRAY_UINT (ai->num_references, v_ann->uid))++; /* If this is a store operation, mark OP as being dereferenced to store, otherwise mark it as being dereferenced to load. */ if (is_store) bitmap_set_bit (ai->dereferenced_ptrs_store, v_ann->uid); else bitmap_set_bit (ai->dereferenced_ptrs_load, v_ann->uid); } if (stmt_escapes_p && num_derefs < 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; /* If the statement makes a function call, assume that pointer OP will be dereferenced in a store operation inside the called function. */ if (get_call_expr_in (stmt)) { bitmap_set_bit (ai->dereferenced_ptrs_store, v_ann->uid); pi->is_dereferenced = 1; } } } /* Update reference counter for definitions to any potentially aliased variable. This is used in the alias grouping heuristics. */ FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_DEF) { tree var = SSA_NAME_VAR (op); var_ann_t ann = var_ann (var); bitmap_set_bit (ai->written_vars, ann->uid); if (may_be_aliased (var)) (VARRAY_UINT (ai->num_references, ann->uid))++; if (POINTER_TYPE_P (TREE_TYPE (op))) collect_points_to_info_for (ai, op); } /* Mark variables in V_MAY_DEF operands as being written to. */ FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_VIRTUAL_DEFS) { tree var = SSA_NAME_VAR (op); var_ann_t ann = var_ann (var); bitmap_set_bit (ai->written_vars, ann->uid); } /* After promoting variables and computing aliasing we will need to re-scan most statements. FIXME: Try to minimize the number of statements re-scanned. It's not really necessary to re-scan *all* statements. */ modify_stmt (stmt); } } timevar_pop (TV_TREE_PTA); } /* 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 (struct alias_info *ai) { size_t i; for (i = 0; i < VARRAY_ACTIVE_SIZE (ai->processed_ptrs); i++) { tree ptr = VARRAY_TREE (ai->processed_ptrs, i); struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr); if (pi->pt_anything || !pi->is_dereferenced) { /* No name tags for pointers that have not been dereferenced or point to an arbitrary location. */ pi->name_mem_tag = NULL_TREE; continue; } if (pi->pt_vars && !bitmap_empty_p (pi->pt_vars)) { size_t j; tree old_name_tag = pi->name_mem_tag; /* 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). */ for (j = 0; j < i; j++) { tree q = VARRAY_TREE (ai->processed_ptrs, j); struct ptr_info_def *qi = SSA_NAME_PTR_INFO (q); if (qi && qi->pt_vars && qi->name_mem_tag && bitmap_equal_p (pi->pt_vars, qi->pt_vars)) { pi->name_mem_tag = qi->name_mem_tag; break; } } /* 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) bitmap_set_bit (vars_to_rename, var_ann (old_name_tag)->uid); } else if (pi->pt_malloc) { /* Otherwise, create a unique name tag for this pointer. */ pi->name_mem_tag = get_nmt_for (ptr); } else { /* Only pointers that may point to malloc or other variables may receive a name tag. If the pointer does not point to a known spot, we should use type tags. */ set_pt_anything (ptr); continue; } TREE_THIS_VOLATILE (pi->name_mem_tag) |= TREE_THIS_VOLATILE (TREE_TYPE (TREE_TYPE (ptr))); /* Mark the new name tag for renaming. */ bitmap_set_bit (vars_to_rename, var_ann (pi->name_mem_tag)->uid); } } /* 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; create_name_tags (ai); for (i = 0; i < VARRAY_ACTIVE_SIZE (ai->processed_ptrs); i++) { unsigned j; tree ptr = VARRAY_TREE (ai->processed_ptrs, i); struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr); var_ann_t v_ann = var_ann (SSA_NAME_VAR (ptr)); bitmap_iterator bi; if (pi->value_escapes_p || pi->pt_anything) { /* If PTR escapes or may point to anything, then its associated memory tags and pointed-to variables are call-clobbered. */ if (pi->name_mem_tag) mark_call_clobbered (pi->name_mem_tag); if (v_ann->type_mem_tag) mark_call_clobbered (v_ann->type_mem_tag); if (pi->pt_vars) EXECUTE_IF_SET_IN_BITMAP (pi->pt_vars, 0, j, bi) { mark_call_clobbered (referenced_var (j)); } } /* 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) EXECUTE_IF_SET_IN_BITMAP (pi->pt_vars, 0, j, bi) { add_may_alias (pi->name_mem_tag, referenced_var (j)); add_may_alias (v_ann->type_mem_tag, referenced_var (j)); } /* If the name tag is call clobbered, so is the type tag associated with the base VAR_DECL. */ if (pi->name_mem_tag && v_ann->type_mem_tag && is_call_clobbered (pi->name_mem_tag)) mark_call_clobbered (v_ann->type_mem_tag); } } /* 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 type memory tag (TMT) if their alias sets conflict. V is then marked as an alias tag so that the operand scanner knows that statements containing V have aliased operands. */ static void compute_flow_insensitive_aliasing (struct alias_info *ai) { size_t i; /* Initialize counter for the total number of virtual operands that aliasing will introduce. When AI->TOTAL_ALIAS_VOPS goes beyond the threshold set by --params max-alias-vops, we enable alias grouping. */ ai->total_alias_vops = 0; /* For every pointer P, determine which addressable variables may alias with P's type memory tag. */ for (i = 0; i < ai->num_pointers; i++) { size_t j; struct alias_map_d *p_map = ai->pointers[i]; tree tag = var_ann (p_map->var)->type_mem_tag; var_ann_t tag_ann = var_ann (tag); p_map->total_alias_vops = 0; p_map->may_aliases = sbitmap_alloc (num_referenced_vars); sbitmap_zero (p_map->may_aliases); for (j = 0; j < ai->num_addressable_vars; j++) { struct alias_map_d *v_map; var_ann_t v_ann; tree var; bool tag_stored_p, var_stored_p; v_map = ai->addressable_vars[j]; var = v_map->var; v_ann = var_ann (var); /* Skip memory tags and variables that have never been written to. We also need to check if the variables are call-clobbered because they may be overwritten by function calls. Note this is effectively random accessing elements in the sparse bitset, which can be highly inefficient. So we first check the call_clobbered status of the tag and variable before querying the bitmap. */ tag_stored_p = is_call_clobbered (tag) || bitmap_bit_p (ai->written_vars, tag_ann->uid); var_stored_p = is_call_clobbered (var) || bitmap_bit_p (ai->written_vars, v_ann->uid); if (!tag_stored_p && !var_stored_p) continue; if (may_alias_p (p_map->var, p_map->set, var, v_map->set)) { size_t num_tag_refs, num_var_refs; num_tag_refs = VARRAY_UINT (ai->num_references, tag_ann->uid); num_var_refs = VARRAY_UINT (ai->num_references, v_ann->uid); /* Add VAR to TAG's may-aliases set. */ add_may_alias (tag, var); /* Update the total number of virtual operands due to aliasing. Since we are adding one more alias to TAG's may-aliases set, the total number of virtual operands due to aliasing will be increased by the number of references made to VAR and TAG (every reference to TAG will also count as a reference to VAR). */ ai->total_alias_vops += (num_var_refs + num_tag_refs); p_map->total_alias_vops += (num_var_refs + num_tag_refs); /* Update the bitmap used to represent TAG's alias set in case we need to group aliases. */ SET_BIT (p_map->may_aliases, var_ann (var)->uid); } } } /* 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 TMT.1 and TMT.2 such that may-aliases (TMT.1) = { a } may-aliases (TMT.2) = { b } and the alias set number of TMT.1 conflicts with that of TMT.2. Since they don't have symbols in common, loads and stores from TMT.1 and TMT.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. */ for (i = 0; i < ai->num_pointers; i++) { size_t j; struct alias_map_d *p_map1 = ai->pointers[i]; tree tag1 = var_ann (p_map1->var)->type_mem_tag; sbitmap may_aliases1 = p_map1->may_aliases; for (j = i + 1; j < ai->num_pointers; j++) { struct alias_map_d *p_map2 = ai->pointers[j]; tree tag2 = var_ann (p_map2->var)->type_mem_tag; sbitmap may_aliases2 = p_map2->may_aliases; /* If the pointers may not point to each other, do nothing. */ if (!may_alias_p (p_map1->var, p_map1->set, p_map2->var, p_map2->set)) continue; /* The two pointers may alias each other. If they already have symbols in common, do nothing. */ if (sbitmap_any_common_bits (may_aliases1, may_aliases2)) continue; if (sbitmap_first_set_bit (may_aliases2) >= 0) { size_t k; /* Add all the aliases for TAG2 into TAG1's alias set. FIXME, update grouping heuristic counters. */ EXECUTE_IF_SET_IN_SBITMAP (may_aliases2, 0, k, add_may_alias (tag1, referenced_var (k))); sbitmap_a_or_b (may_aliases1, may_aliases1, may_aliases2); } else { /* Since TAG2 does not have any aliases of its own, add TAG2 itself to the alias set of TAG1. */ add_may_alias (tag1, tag2); SET_BIT (may_aliases1, var_ann (tag2)->uid); } } } if (dump_file) fprintf (dump_file, "%s: Total number of aliased vops: %ld\n", get_name (current_function_decl), ai->total_alias_vops); /* Determine if we need to enable alias grouping. */ if (ai->total_alias_vops >= MAX_ALIASED_VOPS) group_aliases (ai); } /* Comparison function for qsort used in group_aliases. */ static int total_alias_vops_cmp (const void *p, const void *q) { const struct alias_map_d **p1 = (const struct alias_map_d **)p; const struct alias_map_d **p2 = (const struct alias_map_d **)q; long n1 = (*p1)->total_alias_vops; long n2 = (*p2)->total_alias_vops; /* We want to sort in descending order. */ return (n1 > n2 ? -1 : (n1 == n2) ? 0 : 1); } /* Group all the aliases for TAG to make TAG represent all the variables in its alias set. Update the total number of virtual operands due to aliasing (AI->TOTAL_ALIAS_VOPS). This function will make TAG be the unique alias tag for all the variables in its may-aliases. So, given: may-aliases(TAG) = { V1, V2, V3 } This function will group the variables into: may-aliases(V1) = { TAG } may-aliases(V2) = { TAG } may-aliases(V2) = { TAG } */ static void group_aliases_into (tree tag, sbitmap tag_aliases, struct alias_info *ai) { size_t i; var_ann_t tag_ann = var_ann (tag); size_t num_tag_refs = VARRAY_UINT (ai->num_references, tag_ann->uid); EXECUTE_IF_SET_IN_SBITMAP (tag_aliases, 0, i, { tree var = referenced_var (i); var_ann_t ann = var_ann (var); /* Make TAG the unique alias of VAR. */ ann->is_alias_tag = 0; ann->may_aliases = NULL; /* Note that VAR and TAG may be the same if the function has no addressable variables (see the discussion at the end of setup_pointers_and_addressables). */ if (var != tag) add_may_alias (var, tag); /* Reduce total number of virtual operands contributed by TAG on behalf of VAR. Notice that the references to VAR itself won't be removed. We will merely replace them with references to TAG. */ ai->total_alias_vops -= num_tag_refs; }); /* We have reduced the number of virtual operands that TAG makes on behalf of all the variables formerly aliased with it. However, we have also "removed" all the virtual operands for TAG itself, so we add them back. */ ai->total_alias_vops += num_tag_refs; /* TAG no longer has any aliases. */ tag_ann->may_aliases = NULL; } /* Group may-aliases sets to reduce the number of virtual operands due to aliasing. 1- Sort the list of pointers in decreasing number of contributed virtual operands. 2- Take the first entry in AI->POINTERS and revert the role of the memory tag and its aliases. Usually, whenever an aliased variable Vi is found to alias with a memory tag T, we add Vi to the may-aliases set for T. Meaning that after alias analysis, we will have: may-aliases(T) = { V1, V2, V3, ..., Vn } This means that every statement that references T, will get 'n' virtual operands for each of the Vi tags. But, when alias grouping is enabled, we make T an alias tag and add it to the alias set of all the Vi variables: may-aliases(V1) = { T } may-aliases(V2) = { T } ... may-aliases(Vn) = { T } This has two effects: (a) statements referencing T will only get a single virtual operand, and, (b) all the variables Vi will now appear to alias each other. So, we lose alias precision to improve compile time. But, in theory, a program with such a high level of aliasing should not be very optimizable in the first place. 3- Since variables may be in the alias set of more than one memory tag, the grouping done in step (2) needs to be extended to all the memory tags that have a non-empty intersection with the may-aliases set of tag T. For instance, if we originally had these may-aliases sets: may-aliases(T) = { V1, V2, V3 } may-aliases(R) = { V2, V4 } In step (2) we would have reverted the aliases for T as: may-aliases(V1) = { T } may-aliases(V2) = { T } may-aliases(V3) = { T } But note that now V2 is no longer aliased with R. We could add R to may-aliases(V2), but we are in the process of grouping aliases to reduce virtual operands so what we do is add V4 to the grouping to obtain: may-aliases(V1) = { T } may-aliases(V2) = { T } may-aliases(V3) = { T } may-aliases(V4) = { T } 4- If the total number of virtual operands due to aliasing is still above the threshold set by max-alias-vops, go back to (2). */ static void group_aliases (struct alias_info *ai) { size_t i; /* Sort the POINTERS array in descending order of contributed virtual operands. */ qsort (ai->pointers, ai->num_pointers, sizeof (struct alias_map_d *), total_alias_vops_cmp); /* For every pointer in AI->POINTERS, reverse the roles of its tag and the tag's may-aliases set. */ for (i = 0; i < ai->num_pointers; i++) { size_t j; tree tag1 = var_ann (ai->pointers[i]->var)->type_mem_tag; sbitmap tag1_aliases = ai->pointers[i]->may_aliases; /* Skip tags that have been grouped already. */ if (ai->pointers[i]->grouped_p) continue; /* See if TAG1 had any aliases in common with other type tags. If we find a TAG2 with common aliases with TAG1, add TAG2's aliases into TAG1. */ for (j = i + 1; j < ai->num_pointers; j++) { sbitmap tag2_aliases = ai->pointers[j]->may_aliases; if (sbitmap_any_common_bits (tag1_aliases, tag2_aliases)) { tree tag2 = var_ann (ai->pointers[j]->var)->type_mem_tag; sbitmap_a_or_b (tag1_aliases, tag1_aliases, tag2_aliases); /* TAG2 does not need its aliases anymore. */ sbitmap_zero (tag2_aliases); var_ann (tag2)->may_aliases = NULL; /* TAG1 is the unique alias of TAG2. */ add_may_alias (tag2, tag1); ai->pointers[j]->grouped_p = true; } } /* Now group all the aliases we collected into TAG1. */ group_aliases_into (tag1, tag1_aliases, ai); /* If we've reduced total number of virtual operands below the threshold, stop. */ if (ai->total_alias_vops < MAX_ALIASED_VOPS) break; } /* Finally, all the variables that have been grouped cannot be in the may-alias set of name memory tags. Suppose that we have grouped the aliases in this code so that may-aliases(a) = TMT.20 p_5 = &a; ... # a_9 = V_MAY_DEF <a_8> p_5->field = 0 ... Several modifications to TMT.20 ... # VUSE <a_9> x_30 = p_5->field Since p_5 points to 'a', the optimizers will try to propagate 0 into p_5->field, but that is wrong because there have been modifications to 'TMT.20' in between. To prevent this we have to replace 'a' with 'TMT.20' in the name tag of p_5. */ for (i = 0; i < VARRAY_ACTIVE_SIZE (ai->processed_ptrs); i++) { size_t j; tree ptr = VARRAY_TREE (ai->processed_ptrs, i); tree name_tag = SSA_NAME_PTR_INFO (ptr)->name_mem_tag; varray_type aliases; if (name_tag == NULL_TREE) continue; aliases = var_ann (name_tag)->may_aliases; for (j = 0; aliases && j < VARRAY_ACTIVE_SIZE (aliases); j++) { tree alias = VARRAY_TREE (aliases, j); var_ann_t ann = var_ann (alias); if (ann->mem_tag_kind == NOT_A_TAG && ann->may_aliases) { tree new_alias; gcc_assert (VARRAY_ACTIVE_SIZE (ann->may_aliases) == 1); new_alias = VARRAY_TREE (ann->may_aliases, 0); replace_may_alias (name_tag, j, new_alias); } } } if (dump_file) fprintf (dump_file, "%s: Total number of aliased vops after grouping: %ld%s\n", get_name (current_function_decl), ai->total_alias_vops, (ai->total_alias_vops < 0) ? " (negative values are OK)" : ""); } /* 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 = xcalloc (1, sizeof (*alias_map)); alias_map->var = var; alias_map->set = get_alias_set (var); ai->addressable_vars[ai->num_addressable_vars++] = alias_map; } /* 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 i, n_vars, num_addressable_vars, num_pointers; /* Size up the arrays ADDRESSABLE_VARS and POINTERS. */ num_addressable_vars = num_pointers = 0; for (i = 0; i < num_referenced_vars; i++) { tree var = referenced_var (i); 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)) bitmap_set_bit (ai->dereferenced_ptrs_store, var_ann (var)->uid); 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 type tags are going to be added to POINTERS. */ ai->addressable_vars = xcalloc (num_addressable_vars, sizeof (struct alias_map_d *)); ai->pointers = xcalloc (num_pointers, sizeof (struct alias_map_d *)); ai->num_addressable_vars = 0; ai->num_pointers = 0; /* Since we will be creating type memory tags within this loop, cache the value of NUM_REFERENCED_VARS to avoid processing the additional tags unnecessarily. */ n_vars = num_referenced_vars; for (i = 0; i < n_vars; i++) { tree var = referenced_var (i); var_ann_t v_ann = var_ann (var); /* Name memory tags already have flow-sensitive aliasing information, so they need not be processed by compute_flow_insensitive_aliasing. Similarly, type memory tags are already accounted for when we process their associated pointer. */ if (v_ann->mem_tag_kind != NOT_A_TAG) 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 (ai->addresses_needed, v_ann->uid) && TREE_CODE (var) != RESULT_DECL && !is_global_var (var)) { /* The address of VAR is not needed, remove the addressable bit, so that it can be optimized as a regular variable. */ mark_non_addressable (var); /* Since VAR is now a regular GIMPLE register, we will need to rename VAR into SSA afterwards. */ bitmap_set_bit (vars_to_rename, v_ann->uid); } else { /* Add the variable to the set of addressables. Mostly used when scanning operands for ASM_EXPRs that clobber memory. In those cases, we need to clobber all call-clobbered variables and all addressables. */ bitmap_set_bit (addressable_vars, v_ann->uid); } } /* 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); bitmap_set_bit (vars_to_rename, var_ann (var)->uid); } /* Add pointer variables that have been dereferenced to the POINTERS array and create a type memory tag for them. */ if (POINTER_TYPE_P (TREE_TYPE (var))) { if ((bitmap_bit_p (ai->dereferenced_ptrs_store, v_ann->uid) || bitmap_bit_p (ai->dereferenced_ptrs_load, v_ann->uid))) { tree 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_tmt_for (var, ai); t_ann = var_ann (tag); /* The type tag will need to be renamed into SSA afterwards. Note that we cannot do this inside get_tmt_for because aliasing may run multiple times and we only create type tags the first time. */ bitmap_set_bit (vars_to_rename, t_ann->uid); /* Associate the tag with pointer VAR. */ v_ann->type_mem_tag = tag; /* If pointer VAR has been used in a store operation, then its memory tag must be marked as written-to. */ if (bitmap_bit_p (ai->dereferenced_ptrs_store, v_ann->uid)) bitmap_set_bit (ai->written_vars, t_ann->uid); /* If pointer VAR is a global variable or a PARM_DECL, then its memory tag should be considered a global variable. */ if (TREE_CODE (var) == PARM_DECL || is_global_var (var)) mark_call_clobbered (tag); /* All the dereferences of pointer VAR count as references of TAG. Since TAG can be associated with several pointers, add the dereferences of VAR to the TAG. We may need to grow AI->NUM_REFERENCES because we have been adding name and type tags. */ if (t_ann->uid >= VARRAY_SIZE (ai->num_references)) VARRAY_GROW (ai->num_references, t_ann->uid + 10); VARRAY_UINT (ai->num_references, t_ann->uid) += VARRAY_UINT (ai->num_references, v_ann->uid); } else { /* The pointer has not been dereferenced. If it had a type memory tag, remove it and mark the old tag for renaming to remove it out of the IL. */ var_ann_t ann = var_ann (var); tree tag = ann->type_mem_tag; if (tag) { bitmap_set_bit (vars_to_rename, var_ann (tag)->uid); ann->type_mem_tag = NULL_TREE; } } } } } /* Determine whether to use .GLOBAL_VAR to model call clobbering semantics. At every call site, we need to emit V_MAY_DEF expressions to represent the clobbering effects of the call for variables whose address escapes the current function. One approach is to group all call-clobbered variables into a single representative that is used as an alias of every call-clobbered variable (.GLOBAL_VAR). This works well, but it ties the optimizer hands because references to any call clobbered variable is a reference to .GLOBAL_VAR. The second approach is to emit a clobbering V_MAY_DEF for every call-clobbered variable at call sites. This is the preferred way in terms of optimization opportunities but it may create too many V_MAY_DEF operands if there are many call clobbered variables and function calls in the function. To decide whether or not to use .GLOBAL_VAR we multiply the number of function calls found by the number of call-clobbered variables. If that product is beyond a certain threshold, as determined by the parameterized values shown below, we use .GLOBAL_VAR. FIXME. This heuristic should be improved. One idea is to use several .GLOBAL_VARs of different types instead of a single one. The thresholds have been derived from a typical bootstrap cycle, including all target libraries. Compile times were found increase by ~1% compared to using .GLOBAL_VAR. */ static void maybe_create_global_var (struct alias_info *ai) { unsigned i, n_clobbered; bitmap_iterator bi; /* No need to create it, if we have one already. */ if (global_var == NULL_TREE) { /* Count all the call-clobbered variables. */ n_clobbered = 0; EXECUTE_IF_SET_IN_BITMAP (call_clobbered_vars, 0, i, bi) { n_clobbered++; } /* If the number of virtual operands that would be needed to model all the call-clobbered variables is larger than GLOBAL_VAR_THRESHOLD, create .GLOBAL_VAR. Also 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 (ai->num_calls_found * n_clobbered >= (size_t) GLOBAL_VAR_THRESHOLD || (n_clobbered == 0 && ai->num_calls_found > 0 && ai->num_pure_const_calls_found > 0 && ai->num_calls_found > ai->num_pure_const_calls_found)) create_global_var (); } /* Mark all call-clobbered symbols for renaming. Since the initial rewrite into SSA ignored all call sites, we may need to rename .GLOBAL_VAR and the call-clobbered variables. */ EXECUTE_IF_SET_IN_BITMAP (call_clobbered_vars, 0, i, bi) { tree var = referenced_var (i); /* If the function has calls to clobbering functions and .GLOBAL_VAR has been created, make it an alias for all call-clobbered variables. */ if (global_var && var != global_var) add_may_alias (var, global_var); bitmap_set_bit (vars_to_rename, var_ann (var)->uid); } } /* 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. */ static bool may_alias_p (tree ptr, HOST_WIDE_INT mem_alias_set, tree var, HOST_WIDE_INT var_alias_set) { tree mem; var_ann_t v_ann, m_ann; alias_stats.alias_queries++; alias_stats.simple_queries++; /* By convention, a variable cannot alias itself. */ mem = var_ann (ptr)->type_mem_tag; if (mem == var) { alias_stats.alias_noalias++; alias_stats.simple_resolved++; return false; } v_ann = var_ann (var); m_ann = var_ann (mem); gcc_assert (m_ann->mem_tag_kind == TYPE_TAG); alias_stats.tbaa_queries++; /* APPLE LOCAL mainline 4.0.2 4203511 */ /* Delete code for http://gcc.gnu.org/PR22591 */ /* If the alias sets don't conflict then MEM cannot alias VAR. */ if (!alias_sets_conflict_p (mem_alias_set, var_alias_set)) { alias_stats.alias_noalias++; alias_stats.tbaa_resolved++; return false; } alias_stats.alias_mayalias++; return true; } /* Add ALIAS to the set of variables that may alias VAR. */ static void add_may_alias (tree var, tree alias) { size_t i; var_ann_t v_ann = get_var_ann (var); var_ann_t a_ann = get_var_ann (alias); gcc_assert (var != alias); if (v_ann->may_aliases == NULL) VARRAY_TREE_INIT (v_ann->may_aliases, 2, "aliases"); /* Avoid adding duplicates. */ for (i = 0; i < VARRAY_ACTIVE_SIZE (v_ann->may_aliases); i++) if (alias == VARRAY_TREE (v_ann->may_aliases, i)) return; /* If VAR is a call-clobbered variable, so is its new ALIAS. FIXME, call-clobbering should only depend on whether an address escapes. It should be independent of aliasing. */ if (is_call_clobbered (var)) mark_call_clobbered (alias); /* Likewise. If ALIAS is call-clobbered, so is VAR. */ else if (is_call_clobbered (alias)) mark_call_clobbered (var); VARRAY_PUSH_TREE (v_ann->may_aliases, alias); a_ann->is_alias_tag = 1; } /* Replace alias I in the alias sets of VAR with NEW_ALIAS. */ static void replace_may_alias (tree var, size_t i, tree new_alias) { var_ann_t v_ann = var_ann (var); VARRAY_TREE (v_ann->may_aliases, i) = new_alias; /* If VAR is a call-clobbered variable, so is NEW_ALIAS. FIXME, call-clobbering should only depend on whether an address escapes. It should be independent of aliasing. */ if (is_call_clobbered (var)) mark_call_clobbered (new_alias); /* Likewise. If NEW_ALIAS is call-clobbered, so is VAR. */ else if (is_call_clobbered (new_alias)) mark_call_clobbered (var); } /* 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; pi->pt_malloc = 0; /* 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) { bitmap_set_bit (vars_to_rename, var_ann (pi->name_mem_tag)->uid); pi->name_mem_tag = NULL_TREE; } } /* Mark pointer PTR as pointing to a malloc'd memory area. */ static void set_pt_malloc (tree ptr) { struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr); /* If the pointer has already been found to point to arbitrary memory locations, it is unsafe to mark it as pointing to malloc. */ if (pi->pt_anything) return; pi->pt_malloc = 1; } /* Given two different pointers DEST and ORIG. Merge the points-to information in ORIG into DEST. AI contains all the alias information collected up to this point. */ static void merge_pointed_to_info (struct alias_info *ai, tree dest, tree orig) { struct ptr_info_def *dest_pi, *orig_pi; gcc_assert (dest != orig); /* Make sure we have points-to information for ORIG. */ collect_points_to_info_for (ai, orig); dest_pi = get_ptr_info (dest); orig_pi = SSA_NAME_PTR_INFO (orig); if (orig_pi) { gcc_assert (orig_pi != dest_pi); /* Notice that we never merge PT_MALLOC. This attribute is only true if the pointer is the result of a malloc() call. Otherwise, we can end up in this situation: P_i = malloc (); ... P_j = P_i + X; P_j would be marked as PT_MALLOC, however we currently do not handle cases of more than one pointer pointing to the same malloc'd area. FIXME: If the merging comes from an expression that preserves the PT_MALLOC attribute (copy assignment, address arithmetic), we ought to merge PT_MALLOC, but then both pointers would end up getting different name tags because create_name_tags is not smart enough to determine that the two come from the same malloc call. Copy propagation before aliasing should cure this. */ dest_pi->pt_malloc = 0; if (orig_pi->pt_malloc || orig_pi->pt_anything) set_pt_anything (dest); dest_pi->pt_null |= orig_pi->pt_null; if (!dest_pi->pt_anything && orig_pi->pt_vars && !bitmap_empty_p (orig_pi->pt_vars)) { if (dest_pi->pt_vars == NULL) { dest_pi->pt_vars = BITMAP_GGC_ALLOC (); bitmap_copy (dest_pi->pt_vars, orig_pi->pt_vars); } else bitmap_ior_into (dest_pi->pt_vars, orig_pi->pt_vars); } } else set_pt_anything (dest); } /* Add EXPR to the list of expressions pointed-to by PTR. */ static void add_pointed_to_expr (struct alias_info *ai, tree ptr, tree expr) { if (TREE_CODE (expr) == WITH_SIZE_EXPR) expr = TREE_OPERAND (expr, 0); get_ptr_info (ptr); if (TREE_CODE (expr) == CALL_EXPR && (call_expr_flags (expr) & (ECF_MALLOC | ECF_MAY_BE_ALLOCA))) { /* If EXPR is a malloc-like call, then the area pointed to PTR is guaranteed to not alias with anything else. */ set_pt_malloc (ptr); } else if (TREE_CODE (expr) == ADDR_EXPR) { /* Found P_i = ADDR_EXPR */ add_pointed_to_var (ai, ptr, expr); } else if (TREE_CODE (expr) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (expr))) { /* Found P_i = Q_j. */ merge_pointed_to_info (ai, ptr, expr); } else if (TREE_CODE (expr) == PLUS_EXPR || TREE_CODE (expr) == MINUS_EXPR) { /* Found P_i = PLUS_EXPR or P_i = MINUS_EXPR */ tree op0 = TREE_OPERAND (expr, 0); tree op1 = TREE_OPERAND (expr, 1); /* Both operands may be of pointer type. FIXME: Shouldn't we just expect PTR + OFFSET always? */ if (POINTER_TYPE_P (TREE_TYPE (op0)) && TREE_CODE (op0) != INTEGER_CST) { if (TREE_CODE (op0) == SSA_NAME) merge_pointed_to_info (ai, ptr, op0); else if (TREE_CODE (op0) == ADDR_EXPR) add_pointed_to_var (ai, ptr, op0); else set_pt_anything (ptr); } if (POINTER_TYPE_P (TREE_TYPE (op1)) && TREE_CODE (op1) != INTEGER_CST) { if (TREE_CODE (op1) == SSA_NAME) merge_pointed_to_info (ai, ptr, op1); else if (TREE_CODE (op1) == ADDR_EXPR) add_pointed_to_var (ai, ptr, op1); else set_pt_anything (ptr); } /* Neither operand is a pointer? VAR can be pointing anywhere. FIXME: Shouldn't we abort here? If we get here, we found PTR = INT_CST + INT_CST, which should not be a valid pointer expression. */ if (!(POINTER_TYPE_P (TREE_TYPE (op0)) && TREE_CODE (op0) != INTEGER_CST) && !(POINTER_TYPE_P (TREE_TYPE (op1)) && TREE_CODE (op1) != INTEGER_CST)) set_pt_anything (ptr); } else if (integer_zerop (expr)) { /* EXPR is the NULL pointer. Mark PTR as pointing to NULL. */ SSA_NAME_PTR_INFO (ptr)->pt_null = 1; } else { /* If we can't recognize the expression, assume that PTR may point anywhere. */ set_pt_anything (ptr); } } /* If VALUE is of the form &DECL, add DECL to the set of variables pointed-to by PTR. Otherwise, add VALUE as a pointed-to expression by PTR. AI points to the collected alias information. */ static void add_pointed_to_var (struct alias_info *ai, tree ptr, tree value) { struct ptr_info_def *pi = get_ptr_info (ptr); tree pt_var; size_t uid; gcc_assert (TREE_CODE (value) == ADDR_EXPR); pt_var = TREE_OPERAND (value, 0); if (REFERENCE_CLASS_P (pt_var)) pt_var = get_base_address (pt_var); if (pt_var && SSA_VAR_P (pt_var)) { uid = var_ann (pt_var)->uid; bitmap_set_bit (ai->addresses_needed, uid); if (pi->pt_vars == NULL) pi->pt_vars = BITMAP_GGC_ALLOC (); bitmap_set_bit (pi->pt_vars, uid); /* If the variable is a global, mark the pointer as pointing to global memory (which will make its tag a global variable). */ if (is_global_var (pt_var)) pi->pt_global_mem = 1; } } /* Callback for walk_use_def_chains to gather points-to information from the SSA web. VAR is an SSA variable or a GIMPLE expression. STMT is the statement that generates the SSA variable or, if STMT is a PHI_NODE, VAR is one of the PHI arguments. DATA is a pointer to a structure of type ALIAS_INFO. */ static bool collect_points_to_info_r (tree var, tree stmt, void *data) { struct alias_info *ai = (struct alias_info *) data; if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Visiting use-def links for "); print_generic_expr (dump_file, var, dump_flags); fprintf (dump_file, "\n"); } switch (TREE_CODE (stmt)) { case RETURN_EXPR: if (TREE_CODE (TREE_OPERAND (stmt, 0)) != MODIFY_EXPR) abort (); stmt = TREE_OPERAND (stmt, 0); /* FALLTHRU */ case MODIFY_EXPR: { tree rhs = TREE_OPERAND (stmt, 1); STRIP_NOPS (rhs); add_pointed_to_expr (ai, var, rhs); break; } case ASM_EXPR: /* Pointers defined by __asm__ statements can point anywhere. */ set_pt_anything (var); break; case NOP_EXPR: if (IS_EMPTY_STMT (stmt)) { tree decl = SSA_NAME_VAR (var); if (TREE_CODE (decl) == PARM_DECL) add_pointed_to_expr (ai, var, decl); else if (DECL_INITIAL (decl)) add_pointed_to_expr (ai, var, DECL_INITIAL (decl)); else add_pointed_to_expr (ai, var, decl); } break; case PHI_NODE: { /* It STMT is a PHI node, then VAR is one of its arguments. The variable that we are analyzing is the LHS of the PHI node. */ tree lhs = PHI_RESULT (stmt); switch (TREE_CODE (var)) { case ADDR_EXPR: add_pointed_to_var (ai, lhs, var); break; case SSA_NAME: /* Avoid unnecessary merges. */ if (lhs != var) merge_pointed_to_info (ai, lhs, var); break; default: gcc_assert (is_gimple_min_invariant (var)); add_pointed_to_expr (ai, lhs, var); break; } break; } default: gcc_unreachable (); } return false; } /* 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. AI points to the alias information collected so far. */ static bool is_escape_site (tree stmt, struct alias_info *ai) { tree call = get_call_expr_in (stmt); if (call != NULL_TREE) { ai->num_calls_found++; if (!TREE_SIDE_EFFECTS (call)) ai->num_pure_const_calls_found++; return true; } else if (TREE_CODE (stmt) == ASM_EXPR) return true; else if (TREE_CODE (stmt) == MODIFY_EXPR) { tree lhs = TREE_OPERAND (stmt, 0); /* 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 true; /* If the RHS is a conversion between a pointer and an integer, the pointer escapes since we can't track the integer. */ if ((TREE_CODE (TREE_OPERAND (stmt, 1)) == NOP_EXPR || TREE_CODE (TREE_OPERAND (stmt, 1)) == CONVERT_EXPR || TREE_CODE (TREE_OPERAND (stmt, 1)) == VIEW_CONVERT_EXPR) && POINTER_TYPE_P (TREE_TYPE (TREE_OPERAND (TREE_OPERAND (stmt, 1), 0))) && !POINTER_TYPE_P (TREE_TYPE (TREE_OPERAND (stmt, 1)))) return true; /* If the LHS is an SSA name, it can't possibly represent a non-local memory store. */ if (TREE_CODE (lhs) == SSA_NAME) return false; /* 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 true; } else if (TREE_CODE (stmt) == RETURN_EXPR) return true; return false; } /* 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) { var_ann_t ann; tree tag = create_tmp_var_raw (type, (is_type_tag) ? "TMT" : "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. This also prevents is_gimple_ref frome confusing memory tags with optimizable variables. */ TREE_ADDRESSABLE (tag) = 1; ann = get_var_ann (tag); ann->mem_tag_kind = (is_type_tag) ? TYPE_TAG : NAME_TAG; ann->type_mem_tag = NULL_TREE; /* Add the tag to the symbol table. */ add_referenced_tmp_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); /* If PTR is a PARM_DECL, it points to a global variable or malloc, then its name tag should be considered a global variable. */ if (TREE_CODE (SSA_NAME_VAR (ptr)) == PARM_DECL || pi->pt_malloc || pi->pt_global_mem) mark_call_clobbered (tag); return tag; } /* Return the type 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_tmt_for (tree ptr, struct alias_info *ai) { size_t i; tree tag; tree tag_type = TREE_TYPE (TREE_TYPE (ptr)); HOST_WIDE_INT tag_set = get_alias_set (tag_type); /* 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]; if (tag_set == curr->set) { tag = var_ann (curr->var)->type_mem_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 type tag already, create a new TMT.* artificial variable representing the memory location pointed-to by PTR. */ if (var_ann (ptr)->type_mem_tag == NULL_TREE) tag = create_memory_tag (tag_type, true); else tag = var_ann (ptr)->type_mem_tag; /* 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 = xcalloc (1, sizeof (*alias_map)); 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 type tag has the same alias set as the pointed-to type. */ gcc_assert (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) { 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; add_referenced_tmp_var (global_var); bitmap_set_bit (vars_to_rename, var_ann (global_var)->uid); } /* 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); } /* 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); fprintf (file, "\nFlow-insensitive alias information for %s\n\n", funcname); fprintf (file, "Aliased symbols\n\n"); for (i = 0; i < num_referenced_vars; i++) { tree var = referenced_var (i); if (may_be_aliased (var)) dump_variable (file, var); } fprintf (file, "\nDereferenced pointers\n\n"); for (i = 0; i < num_referenced_vars; i++) { tree var = referenced_var (i); var_ann_t ann = var_ann (var); if (ann->type_mem_tag) dump_variable (file, var); } fprintf (file, "\nType memory tags\n\n"); for (i = 0; i < num_referenced_vars; i++) { tree var = referenced_var (i); var_ann_t ann = var_ann (var); if (ann->mem_tag_kind == TYPE_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 (i = 0; i < num_referenced_vars; i++) { tree var = referenced_var (i); var_ann_t ann = var_ann (var); if (ann->mem_tag_kind == NAME_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_alloc (sizeof (*pi)); memset ((void *)pi, 0, sizeof (*pi)); 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"); if (pi->value_escapes_p) fprintf (file, ", its value escapes"); if (pi->pt_anything) fprintf (file, ", points-to anything"); if (pi->pt_malloc) fprintf (file, ", points-to malloc"); if (pi->pt_null) fprintf (file, ", points-to NULL"); if (pi->pt_vars) { unsigned ix; bitmap_iterator bi; fprintf (file, ", points-to vars: { "); EXECUTE_IF_SET_IN_BITMAP (pi->pt_vars, 0, ix, bi) { print_generic_expr (file, referenced_var (ix), dump_flags); fprintf (file, " "); } fprintf (file, "}"); } } 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) { basic_block bb; block_stmt_iterator si; size_t i; ssa_op_iter iter; const char *fname = lang_hooks.decl_printable_name (current_function_decl, 2); 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 (i = 0; i < num_referenced_vars; i++) { tree var = referenced_var (i); if (POINTER_TYPE_P (TREE_TYPE (var))) { var_ann_t ann = var_ann (var); if (ann->default_def) dump_points_to_info_for (file, ann->default_def); } } /* Dump points-to information for every pointer defined in the program. */ FOR_EACH_BB (bb) { tree phi; for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) { tree ptr = PHI_RESULT (phi); if (POINTER_TYPE_P (TREE_TYPE (ptr))) dump_points_to_info_for (file, ptr); } for (si = bsi_start (bb); !bsi_end_p (si); bsi_next (&si)) { tree stmt = bsi_stmt (si); tree def; FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF) if (POINTER_TYPE_P (TREE_TYPE (def))) dump_points_to_info_for (file, def); } } fprintf (file, "\n"); } /* Dump points-to info pointed 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) { varray_type aliases; if (TREE_CODE (var) == SSA_NAME) var = SSA_NAME_VAR (var); aliases = var_ann (var)->may_aliases; if (aliases) { size_t i; fprintf (file, "{ "); for (i = 0; i < VARRAY_ACTIVE_SIZE (aliases); i++) { print_generic_expr (file, VARRAY_TREE (aliases, i), 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 (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; /* If we're in unit-at-a-time mode, then we must have seen all occurrences of address-of operators, and so we can trust TREE_ADDRESSABLE. Otherwise we can only be sure the variable isn't addressable if it's local to the current function. */ if (flag_unit_at_a_time) return false; if (decl_function_context (var) == current_function_decl) return false; return true; }