/* Rewrite a program in Normal form into SSA. Copyright (C) 2001, 2002, 2003, 2004 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 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 "flags.h" #include "rtl.h" #include "tm_p.h" #include "langhooks.h" #include "hard-reg-set.h" #include "basic-block.h" #include "output.h" #include "errors.h" #include "expr.h" #include "function.h" #include "diagnostic.h" #include "bitmap.h" #include "tree-flow.h" #include "tree-gimple.h" #include "tree-inline.h" #include "varray.h" #include "timevar.h" #include "tree-alias-common.h" #include "hashtab.h" #include "tree-dump.h" #include "tree-pass.h" #include "cfgloop.h" #include "domwalk.h" /* This file builds the SSA form for a function as described in: R. Cytron, J. Ferrante, B. Rosen, M. Wegman, and K. Zadeck. Efficiently Computing Static Single Assignment Form and the Control Dependence Graph. ACM Transactions on Programming Languages and Systems, 13(4):451-490, October 1991. */ /* Structure to map a variable VAR to the set of blocks that contain definitions for VAR. */ struct def_blocks_d { /* The variable. */ tree var; /* Blocks that contain definitions of VAR. Bit I will be set if the Ith block contains a definition of VAR. */ bitmap def_blocks; /* Blocks where VAR is live-on-entry. Similar semantics as DEF_BLOCKS. */ bitmap livein_blocks; }; /* Each entry in DEF_BLOCKS contains an element of type STRUCT DEF_BLOCKS_D, mapping a variable VAR to a bitmap describing all the basic blocks where VAR is defined (assigned a new value). It also contains a bitmap of all the blocks where VAR is live-on-entry (i.e., there is a use of VAR in block B without a preceding definition in B). The live-on-entry information is used when computing PHI pruning heuristics. */ static htab_t def_blocks; /* Global data to attach to the main dominator walk structure. */ struct mark_def_sites_global_data { /* This sbitmap contains the variables which are set before they are used in a basic block. We keep it as a global variable solely to avoid the overhead of allocating and deallocating the bitmap. */ sbitmap kills; }; struct rewrite_block_data { varray_type block_defs; }; /* Local functions. */ static void rewrite_finalize_block (struct dom_walk_data *, basic_block); static void rewrite_initialize_block_local_data (struct dom_walk_data *, basic_block, bool); static void rewrite_initialize_block (struct dom_walk_data *, basic_block); static void rewrite_add_phi_arguments (struct dom_walk_data *, basic_block); static void mark_def_sites (struct dom_walk_data *walk_data, basic_block bb, block_stmt_iterator); static void mark_def_sites_initialize_block (struct dom_walk_data *walk_data, basic_block bb); static void compute_global_livein (bitmap, bitmap); static void set_def_block (tree, basic_block); static void set_livein_block (tree, basic_block); static bool prepare_operand_for_rename (tree *op_p, size_t *uid_p, bool); static void insert_phi_nodes (bitmap *); static void rewrite_stmt (struct dom_walk_data *, basic_block, block_stmt_iterator); static inline void rewrite_operand (tree *); static void insert_phi_nodes_for (tree, bitmap *, varray_type *); static tree get_reaching_def (tree); static hashval_t def_blocks_hash (const void *); static int def_blocks_eq (const void *, const void *); static void def_blocks_free (void *); static int debug_def_blocks_r (void **, void *); static inline struct def_blocks_d *get_def_blocks_for (tree); static inline struct def_blocks_d *find_def_blocks_for (tree); static void htab_statistics (FILE *, htab_t); /* Compute global livein information given the set of blockx where an object is locally live at the start of the block (LIVEIN) and the set of blocks where the object is defined (DEF_BLOCKS). Note: This routine augments the existing local livein information to include global livein (i.e., it modifies the underlying bitmap for LIVEIN). */ static void compute_global_livein (bitmap livein, bitmap def_blocks) { basic_block bb, *worklist, *tos; int i; tos = worklist = (basic_block *) xmalloc (sizeof (basic_block) * (last_basic_block + 1)); EXECUTE_IF_SET_IN_BITMAP (livein, 0, i, { *tos++ = BASIC_BLOCK (i); }); /* Iterate until the worklist is empty. */ while (tos != worklist) { edge e; /* Pull a block off the worklist. */ bb = *--tos; /* For each predecessor block. */ for (e = bb->pred; e; e = e->pred_next) { basic_block pred = e->src; int pred_index = pred->index; /* None of this is necessary for the entry block. */ if (pred != ENTRY_BLOCK_PTR && ! bitmap_bit_p (livein, pred_index) && ! bitmap_bit_p (def_blocks, pred_index)) { *tos++ = pred; bitmap_set_bit (livein, pred_index); } } } free (worklist); } /* Block initialization routine for mark_def_sites. Clear the KILLS bitmap at the start of each block. */ static void mark_def_sites_initialize_block (struct dom_walk_data *walk_data, basic_block bb ATTRIBUTE_UNUSED) { struct mark_def_sites_global_data *gd = walk_data->global_data; sbitmap kills = gd->kills; sbitmap_zero (kills); } /* Call back for walk_dominator_tree used to collect definition sites for every variable in the function. For every statement S in block BB: 1- Variables defined by S in DEF_OPS(S) are marked in the bitmap WALK_DATA->GLOBAL_DATA->KILLS. 2- If S uses a variable VAR and there is no preceding kill of VAR, then it is marked in marked in the LIVEIN_BLOCKS bitmap associated with VAR. This information is used to determine which variables are live across block boundaries to reduce the number of PHI nodes we create. */ static void mark_def_sites (struct dom_walk_data *walk_data, basic_block bb, block_stmt_iterator bsi) { struct mark_def_sites_global_data *gd = walk_data->global_data; sbitmap kills = gd->kills; vdef_optype vdefs; vuse_optype vuses; def_optype defs; use_optype uses; size_t i, uid; tree stmt; stmt_ann_t ann; /* Mark all the blocks that have definitions for each variable in the VARS_TO_RENAME bitmap. */ stmt = bsi_stmt (bsi); get_stmt_operands (stmt); ann = stmt_ann (stmt); /* If a variable is used before being set, then the variable is live across a block boundary, so mark it live-on-entry to BB. */ uses = USE_OPS (ann); for (i = 0; i < NUM_USES (uses); i++) { tree *use_p = USE_OP_PTR (uses, i); if (prepare_operand_for_rename (use_p, &uid, true) && !TEST_BIT (kills, uid)) set_livein_block (*use_p, bb); } /* Similarly for virtual uses. */ vuses = VUSE_OPS (ann); for (i = 0; i < NUM_VUSES (vuses); i++) { tree *use_p = VUSE_OP_PTR (vuses, i); if (prepare_operand_for_rename (use_p, &uid, true)) set_livein_block (*use_p, bb); } /* Note that virtual definitions are irrelevant for computing KILLS because a VDEF does not constitute a killing definition of the variable. However, the operand of a virtual definitions is a use of the variable, so it may cause the variable to be considered live-on-entry. */ vdefs = VDEF_OPS (ann); for (i = 0; i < NUM_VDEFS (vdefs); i++) { if (prepare_operand_for_rename (VDEF_OP_PTR (vdefs, i), &uid, true)) { /* If we do not already have an SSA_NAME for our destination, then set the destination to the source. */ if (TREE_CODE (VDEF_RESULT (vdefs, i)) != SSA_NAME) VDEF_RESULT (vdefs, i) = VDEF_OP (vdefs, i); set_livein_block (VDEF_OP (vdefs, i), bb); set_def_block (VDEF_RESULT (vdefs, i), bb); } } /* Now process the definition made by this statement. Mark the variables in KILLS. */ defs = DEF_OPS (ann); for (i = 0; i < NUM_DEFS (defs); i++) { tree *def_p = DEF_OP_PTR (defs, i); if (prepare_operand_for_rename (def_p, &uid, false)) { set_def_block (*def_p, bb); SET_BIT (kills, uid); } } } /* Mark block BB as the definition site for variable VAR. */ static void set_def_block (tree var, basic_block bb) { struct def_blocks_d *db_p; enum need_phi_state state; if (TREE_CODE (var) == SSA_NAME) var = SSA_NAME_VAR (var); state = var_ann (var)->need_phi_state; db_p = get_def_blocks_for (var); /* Set the bit corresponding to the block where VAR is defined. */ bitmap_set_bit (db_p->def_blocks, bb->index); /* Keep track of whether or not we may need to insert phi nodes. If we are in the UNKNOWN state, then this is the first definition of VAR. Additionally, we have not seen any uses of VAR yet, so we do not need a phi node for this variable at this time (i.e., transition to NEED_PHI_STATE_NO). If we are in any other state, then we either have multiple definitions of this variable occurring in different blocks or we saw a use of the variable which was not dominated by the block containing the definition(s). In this case we may need a PHI node, so enter state NEED_PHI_STATE_MAYBE. */ if (state == NEED_PHI_STATE_UNKNOWN) var_ann (var)->need_phi_state = NEED_PHI_STATE_NO; else var_ann (var)->need_phi_state = NEED_PHI_STATE_MAYBE; } /* Mark block BB as having VAR live at the entry to BB. */ static void set_livein_block (tree var, basic_block bb) { struct def_blocks_d *db_p; enum need_phi_state state = var_ann (var)->need_phi_state; db_p = get_def_blocks_for (var); /* Set the bit corresponding to the block where VAR is live in. */ bitmap_set_bit (db_p->livein_blocks, bb->index); /* Keep track of whether or not we may need to insert phi nodes. If we reach here in NEED_PHI_STATE_NO, see if this use is dominated by the single block containing the definition(s) of this variable. If it is, then we remain in NEED_PHI_STATE_NO, otherwise we transition to NEED_PHI_STATE_MAYBE. */ if (state == NEED_PHI_STATE_NO) { int def_block_index = bitmap_first_set_bit (db_p->def_blocks); if (def_block_index == -1 || ! dominated_by_p (CDI_DOMINATORS, bb, BASIC_BLOCK (def_block_index))) var_ann (var)->need_phi_state = NEED_PHI_STATE_MAYBE; } else var_ann (var)->need_phi_state = NEED_PHI_STATE_MAYBE; } /* If the operand pointed to by OP_P needs to be renamed, then 1. If OP_P is used (rather than set), then strip away any SSA_NAME wrapping the operand. 2. Set *UID_P to the underlying variable's uid. 3. Return true. Otherwise return false. */ static bool prepare_operand_for_rename (tree *op_p, size_t *uid_p, bool is_use) { tree var = (TREE_CODE (*op_p) != SSA_NAME) ? *op_p : SSA_NAME_VAR (*op_p); *uid_p = var_ann (var)->uid; /* Ignore variables that don't need to be renamed. */ if (vars_to_rename && !bitmap_bit_p (vars_to_rename, *uid_p)) return false; /* The variable needs to be renamed. If this is a use which already has an SSA_NAME, then strip it off. By not throwing away SSA_NAMEs on assignments, we avoid a lot of useless churn of SSA_NAMEs without having to overly complicate the renamer. */ if (TREE_CODE (*op_p) == SSA_NAME && is_use) *op_p = var; return true; } /* Helper for insert_phi_nodes. If VAR needs PHI nodes, insert them at the dominance frontier (DFS) of blocks defining VAR. */ static inline void insert_phi_nodes_1 (tree var, bitmap *dfs, varray_type *work_stack) { var_ann_t ann = var_ann (var); if (ann->need_phi_state != NEED_PHI_STATE_NO) insert_phi_nodes_for (var, dfs, work_stack); } /* Insert PHI nodes at the dominance frontier of blocks with variable definitions. DFS contains the dominance frontier information for the flowgraph. PHI nodes will only be inserted at the dominance frontier of definition blocks for variables whose NEED_PHI_STATE annotation is marked as ``maybe'' or ``unknown'' (computed by mark_def_sites). */ static void insert_phi_nodes (bitmap *dfs) { size_t i; varray_type work_stack; timevar_push (TV_TREE_INSERT_PHI_NODES); /* Array WORK_STACK is a stack of CFG blocks. Each block that contains an assignment or PHI node will be pushed to this stack. */ VARRAY_BB_INIT (work_stack, last_basic_block, "work_stack"); /* Iterate over all variables in VARS_TO_RENAME. For each variable, add to the work list all the blocks that have a definition for the variable. PHI nodes will be added to the dominance frontier blocks of each definition block. */ if (vars_to_rename) EXECUTE_IF_SET_IN_BITMAP (vars_to_rename, 0, i, insert_phi_nodes_1 (referenced_var (i), dfs, &work_stack)); else for (i = 0; i < num_referenced_vars; i++) insert_phi_nodes_1 (referenced_var (i), dfs, &work_stack); timevar_pop (TV_TREE_INSERT_PHI_NODES); } /* Perform a depth-first traversal of the dominator tree looking for variables to rename. BB is the block where to start searching. Renaming is a five step process: 1- Every definition made by PHI nodes at the start of the blocks is registered as the current definition for the corresponding variable. 2- Every statement in BB is rewritten. USE and VUSE operands are rewritten with their corresponding reaching definition. DEF and VDEF targets are registered as new definitions. 3- All the PHI nodes in successor blocks of BB are visited. The argument corresponding to BB is replaced with its current reaching definition. 4- Recursively rewrite every dominator child block of BB. 5- Restore (in reverse order) the current reaching definition for every new definition introduced in this block. This is done so that when we return from the recursive call, all the current reaching definitions are restored to the names that were valid in the dominator parent of BB. */ /* Initialize the local stacks. BLOCK_DEFS is used to save all the existing reaching definitions for the new SSA names introduced in this block. Before registering a new definition for a variable, the existing reaching definition is pushed into this stack so that we can restore it in Step 5. */ static void rewrite_initialize_block_local_data (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, basic_block bb ATTRIBUTE_UNUSED, bool recycled ATTRIBUTE_UNUSED) { #ifdef ENABLE_CHECKING struct rewrite_block_data *bd = (struct rewrite_block_data *)VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack); /* We get cleared memory from the allocator, so if the memory is not cleared, then we are re-using a previously allocated entry. In that case, we can also re-use the underlying virtal arrays. Just make sure we clear them before using them! */ if (recycled && bd->block_defs && VARRAY_ACTIVE_SIZE (bd->block_defs) > 0) abort (); #endif } /* SSA Rewriting Step 1. Initialization, create a block local stack of reaching definitions for new SSA names produced in this block (BLOCK_DEFS). Register new definitions for every PHI node in the block. */ static void rewrite_initialize_block (struct dom_walk_data *walk_data, basic_block bb) { tree phi; struct rewrite_block_data *bd = (struct rewrite_block_data *)VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack); if (dump_file && (dump_flags & TDF_DETAILS)) fprintf (dump_file, "\n\nRenaming block #%d\n\n", bb->index); /* Step 1. Register new definitions for every PHI node in the block. Conceptually, all the PHI nodes are executed in parallel and each PHI node introduces a new version for the associated variable. */ for (phi = phi_nodes (bb); phi; phi = TREE_CHAIN (phi)) { tree result = PHI_RESULT (phi); register_new_def (result, &bd->block_defs); } } /* SSA Rewriting Step 3. Visit all the successor blocks of BB looking for PHI nodes. For every PHI node found, add a new argument containing the current reaching definition for the variable and the edge through which that definition is reaching the PHI node. */ static void rewrite_add_phi_arguments (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, basic_block bb) { edge e; for (e = bb->succ; e; e = e->succ_next) { tree phi; for (phi = phi_nodes (e->dest); phi; phi = TREE_CHAIN (phi)) { tree currdef; /* If this PHI node has already been rewritten, then there is nothing to do for this PHI or any following PHIs since we always add new PHI nodes at the start of the PHI chain. */ if (PHI_REWRITTEN (phi)) break; currdef = get_reaching_def (SSA_NAME_VAR (PHI_RESULT (phi))); add_phi_arg (&phi, currdef, e); } } } /* SSA Rewriting Step 5. Restore the current reaching definition for each variable referenced in the block (in reverse order). */ static void rewrite_finalize_block (struct dom_walk_data *walk_data, basic_block bb ATTRIBUTE_UNUSED) { struct rewrite_block_data *bd = (struct rewrite_block_data *)VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack); /* Step 5. Restore the current reaching definition for each variable referenced in the block (in reverse order). */ while (bd->block_defs && VARRAY_ACTIVE_SIZE (bd->block_defs) > 0) { tree tmp = VARRAY_TOP_TREE (bd->block_defs); tree saved_def, var; VARRAY_POP (bd->block_defs); if (TREE_CODE (tmp) == SSA_NAME) { saved_def = tmp; var = SSA_NAME_VAR (saved_def); } else { saved_def = NULL; var = tmp; } var_ann (var)->current_def = saved_def; } } /* Dump SSA information to FILE. */ void dump_tree_ssa (FILE *file) { basic_block bb; const char *funcname = lang_hooks.decl_printable_name (current_function_decl, 2); fprintf (file, "SSA information for %s\n\n", funcname); FOR_EACH_BB (bb) { dump_bb (bb, file, 0); fputs (" ", file); print_generic_stmt (file, phi_nodes (bb), dump_flags); fputs ("\n\n", file); } } /* Dump SSA information to stderr. */ void debug_tree_ssa (void) { dump_tree_ssa (stderr); } /* Dump SSA statistics on FILE. */ void dump_tree_ssa_stats (FILE *file) { fprintf (file, "\nHash table statistics:\n"); fprintf (file, " def_blocks: "); htab_statistics (file, def_blocks); fprintf (file, "\n"); } /* Dump SSA statistics on stderr. */ void debug_tree_ssa_stats (void) { dump_tree_ssa_stats (stderr); } /* Dump statistics for the hash table HTAB. */ static void htab_statistics (FILE *file, htab_t htab) { fprintf (file, "size %ld, %ld elements, %f collision/search ratio\n", (long) htab_size (htab), (long) htab_elements (htab), htab_collisions (htab)); } /* Insert PHI nodes for variable VAR using the dominance frontier information given in DFS. */ static void insert_phi_nodes_for (tree var, bitmap *dfs, varray_type *work_stack) { struct def_blocks_d *def_map; bitmap phi_insertion_points; int bb_index; def_map = find_def_blocks_for (var); if (def_map == NULL) return; phi_insertion_points = BITMAP_XMALLOC (); EXECUTE_IF_SET_IN_BITMAP (def_map->def_blocks, 0, bb_index, { VARRAY_PUSH_BB (*work_stack, BASIC_BLOCK (bb_index)); }); /* Pop a block off the worklist, add every block that appears in the original block's dfs that we have not already processed to the worklist. Iterate until the worklist is empty. Blocks which are added to the worklist are potential sites for PHI nodes. The iteration step could be done during PHI insertion just as easily. We do it here for historical reasons -- we used to have a heuristic which used the potential PHI insertion points to determine if fully pruned or semi pruned SSA form was appropriate. We now always use fully pruned SSA form. */ while (VARRAY_ACTIVE_SIZE (*work_stack) > 0) { basic_block bb = VARRAY_TOP_BB (*work_stack); int bb_index = bb->index; int dfs_index; VARRAY_POP (*work_stack); EXECUTE_IF_AND_COMPL_IN_BITMAP (dfs[bb_index], phi_insertion_points, 0, dfs_index, { basic_block bb = BASIC_BLOCK (dfs_index); VARRAY_PUSH_BB (*work_stack, bb); bitmap_set_bit (phi_insertion_points, dfs_index); }); } /* Now compute global livein for this variable. Note this modifies def_map->livein_blocks. */ compute_global_livein (def_map->livein_blocks, def_map->def_blocks); /* And insert the PHI nodes. */ EXECUTE_IF_AND_IN_BITMAP (phi_insertion_points, def_map->livein_blocks, 0, bb_index, { create_phi_node (var, BASIC_BLOCK (bb_index)); }); BITMAP_XFREE (phi_insertion_points); } /* SSA Rewriting Step 2. Rewrite every variable used in each statement in the block with its immediate reaching definitions. Update the current definition of a variable when a new real or virtual definition is found. */ static void rewrite_stmt (struct dom_walk_data *walk_data, basic_block bb ATTRIBUTE_UNUSED, block_stmt_iterator si) { size_t i; stmt_ann_t ann; tree stmt; vuse_optype vuses; vdef_optype vdefs; def_optype defs; use_optype uses; struct rewrite_block_data *bd; bd = VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack); stmt = bsi_stmt (si); ann = stmt_ann (stmt); if (dump_file && (dump_flags & TDF_DETAILS)) { fprintf (dump_file, "Renaming statement "); print_generic_stmt (dump_file, stmt, TDF_SLIM); fprintf (dump_file, "\n"); } #if defined ENABLE_CHECKING /* We have just scanned the code for operands. No statement should be modified. */ if (ann->modified) abort (); #endif defs = DEF_OPS (ann); uses = USE_OPS (ann); vuses = VUSE_OPS (ann); vdefs = VDEF_OPS (ann); /* Step 1. Rewrite USES and VUSES in the statement. */ for (i = 0; i < NUM_USES (uses); i++) rewrite_operand (USE_OP_PTR (uses, i)); /* Rewrite virtual uses in the statement. */ for (i = 0; i < NUM_VUSES (vuses); i++) rewrite_operand (VUSE_OP_PTR (vuses, i)); /* Step 2. Register the statement's DEF and VDEF operands. */ for (i = 0; i < NUM_DEFS (defs); i++) { tree *def_p = DEF_OP_PTR (defs, i); if (TREE_CODE (*def_p) != SSA_NAME) *def_p = make_ssa_name (*def_p, stmt); /* FIXME: We shouldn't be registering new defs if the variable doesn't need to be renamed. */ register_new_def (*def_p, &bd->block_defs); } /* Register new virtual definitions made by the statement. */ for (i = 0; i < NUM_VDEFS (vdefs); i++) { rewrite_operand (VDEF_OP_PTR (vdefs, i)); if (TREE_CODE (VDEF_RESULT (vdefs, i)) != SSA_NAME) *VDEF_RESULT_PTR (vdefs, i) = make_ssa_name (VDEF_RESULT (vdefs, i), stmt); /* FIXME: We shouldn't be registering new defs if the variable doesn't need to be renamed. */ register_new_def (VDEF_RESULT (vdefs, i), &bd->block_defs); } } /* Replace the operand pointed by OP_P with its immediate reaching definition. */ static inline void rewrite_operand (tree *op_p) { if (TREE_CODE (*op_p) != SSA_NAME) *op_p = get_reaching_def (*op_p); } /* Register DEF (an SSA_NAME) to be a new definition for its underlying variable (SSA_NAME_VAR (DEF)) and push VAR's current reaching definition into the stack pointed by BLOCK_DEFS_P. */ void register_new_def (tree def, varray_type *block_defs_p) { tree var = SSA_NAME_VAR (def); tree currdef; /* If this variable is set in a single basic block and all uses are dominated by the set(s) in that single basic block, then there is no reason to record anything for this variable in the block local definition stacks. Doing so just wastes time and memory. This is the same test to prune the set of variables which may need PHI nodes. So we just use that information since it's already computed and available for us to use. */ if (var_ann (var)->need_phi_state == NEED_PHI_STATE_NO) { var_ann (var)->current_def = def; return; } currdef = var_ann (var)->current_def; if (! *block_defs_p) VARRAY_TREE_INIT (*block_defs_p, 20, "block_defs"); /* Push the current reaching definition into *BLOCK_DEFS_P. This stack is later used by the dominator tree callbacks to restore the reaching definitions for all the variables defined in the block after a recursive visit to all its immediately dominated blocks. If there is no current reaching definition, then just record the underlying _DECL node. */ VARRAY_PUSH_TREE (*block_defs_p, currdef ? currdef : var); /* Set the current reaching definition for VAR to be DEF. */ var_ann (var)->current_def = def; } /* Return the current definition for variable VAR. If none is found, create a new SSA name to act as the zeroth definition for VAR. If VAR is call clobbered and there exists a more recent definition of GLOBAL_VAR, return the definition for GLOBAL_VAR. This means that VAR has been clobbered by a function call since its last assignment. */ static tree get_reaching_def (tree var) { tree default_d, currdef_var; /* Lookup the current reaching definition for VAR. */ default_d = NULL_TREE; currdef_var = var_ann (var)->current_def; /* If there is no reaching definition for VAR, create and register a default definition for it (if needed). */ if (currdef_var == NULL_TREE) { default_d = default_def (var); if (default_d == NULL_TREE) { default_d = make_ssa_name (var, build_empty_stmt ()); set_default_def (var, default_d); } var_ann (var)->current_def = default_d; } /* Return the current reaching definition for VAR, or the default definition, if we had to create one. */ return (currdef_var) ? currdef_var : default_d; } /* Hashing and equality functions for DEF_BLOCKS. */ static hashval_t def_blocks_hash (const void *p) { return htab_hash_pointer ((const void *)((const struct def_blocks_d *)p)->var); } static int def_blocks_eq (const void *p1, const void *p2) { return ((const struct def_blocks_d *)p1)->var == ((const struct def_blocks_d *)p2)->var; } /* Free memory allocated by one entry in DEF_BLOCKS. */ static void def_blocks_free (void *p) { struct def_blocks_d *entry = p; BITMAP_XFREE (entry->def_blocks); BITMAP_XFREE (entry->livein_blocks); free (entry); } /* Dump the DEF_BLOCKS hash table on stderr. */ void debug_def_blocks (void) { htab_traverse (def_blocks, debug_def_blocks_r, NULL); } /* Callback for htab_traverse to dump the DEF_BLOCKS hash table. */ static int debug_def_blocks_r (void **slot, void *data ATTRIBUTE_UNUSED) { unsigned long i; struct def_blocks_d *db_p = (struct def_blocks_d *) *slot; fprintf (stderr, "VAR: "); print_generic_expr (stderr, db_p->var, dump_flags); fprintf (stderr, ", DEF_BLOCKS: { "); EXECUTE_IF_SET_IN_BITMAP (db_p->def_blocks, 0, i, fprintf (stderr, "%ld ", i)); fprintf (stderr, "}"); fprintf (stderr, ", LIVEIN_BLOCKS: { "); EXECUTE_IF_SET_IN_BITMAP (db_p->livein_blocks, 0, i, fprintf (stderr, "%ld ", i)); fprintf (stderr, "}\n"); return 1; } /* Return the set of blocks where variable VAR is defined and the blocks where VAR is live on entry (livein). Return NULL, if no entry is found in DEF_BLOCKS. */ static inline struct def_blocks_d * find_def_blocks_for (tree var) { struct def_blocks_d dm; dm.var = var; return (struct def_blocks_d *) htab_find (def_blocks, &dm); } /* Return the set of blocks where variable VAR is defined and the blocks where VAR is live on entry (livein). If no entry is found in DEF_BLOCKS, a new one is created and returned. */ static inline struct def_blocks_d * get_def_blocks_for (tree var) { struct def_blocks_d db, *db_p; void **slot; db.var = var; slot = htab_find_slot (def_blocks, (void *) &db, INSERT); if (*slot == NULL) { db_p = xmalloc (sizeof (*db_p)); db_p->var = var; db_p->def_blocks = BITMAP_XMALLOC (); db_p->livein_blocks = BITMAP_XMALLOC (); *slot = (void *) db_p; } else db_p = (struct def_blocks_d *) *slot; return db_p; } /* If a variable V in VARS_TO_RENAME is a pointer, the renaming process will cause us to lose the name memory tags that may have been associated with the various SSA_NAMEs of V. This means that the variables aliased to those name tags also need to be renamed again. FIXME 1- We should either have a better scheme for renaming pointers that doesn't lose name tags or re-run alias analysis to recover points-to information. 2- Currently we just invalidate *all* the name tags. This should be more selective. */ static void invalidate_name_tags (bitmap vars_to_rename) { size_t i; bool rename_name_tags_p; rename_name_tags_p = false; EXECUTE_IF_SET_IN_BITMAP (vars_to_rename, 0, i, if (POINTER_TYPE_P (TREE_TYPE (referenced_var (i)))) { rename_name_tags_p = true; break; }); if (rename_name_tags_p) for (i = 0; i < num_referenced_vars; i++) { var_ann_t ann = var_ann (referenced_var (i)); if (ann->mem_tag_kind == NAME_TAG) { size_t j; varray_type may_aliases = ann->may_aliases; bitmap_set_bit (vars_to_rename, ann->uid); if (ann->may_aliases) for (j = 0; j < VARRAY_ACTIVE_SIZE (may_aliases); j++) { tree var = VARRAY_TREE (may_aliases, j); bitmap_set_bit (vars_to_rename, var_ann (var)->uid); } } } } /* Main entry point into the SSA builder. The renaming process proceeds in five main phases: 1- If VARS_TO_RENAME has any entries, any existing PHI nodes for those variables are removed from the flow graph so that they can be computed again. 2- Compute dominance frontier and immediate dominators, needed to insert PHI nodes and rename the function in dominator tree order. 3- Find and mark all the blocks that define variables (mark_def_sites). 4- Insert PHI nodes at dominance frontiers (insert_phi_nodes). 5- Rename all the blocks (rewrite_initialize_block, rewrite_add_phi_arguments) and statements in the program (rewrite_stmt). Steps 3 and 5 are done using the dominator tree walker (walk_dominator_tree). */ void rewrite_into_ssa (void) { bitmap *dfs; basic_block bb; struct dom_walk_data walk_data; struct mark_def_sites_global_data mark_def_sites_global_data; unsigned int i; timevar_push (TV_TREE_SSA_OTHER); /* Initialize the array of variables to rename. */ if (vars_to_rename != NULL) { invalidate_name_tags (vars_to_rename); /* Now remove all the existing PHI nodes (if any) for the variables that we are about to rename into SSA. */ remove_all_phi_nodes_for (vars_to_rename); } /* Allocate memory for the DEF_BLOCKS hash table. */ def_blocks = htab_create (VARRAY_ACTIVE_SIZE (referenced_vars), def_blocks_hash, def_blocks_eq, def_blocks_free); /* Initialize dominance frontier and immediate dominator bitmaps. Also count the number of predecessors for each block. Doing so can save significant time during PHI insertion for large graphs. */ dfs = (bitmap *) xmalloc (last_basic_block * sizeof (bitmap *)); FOR_EACH_BB (bb) { edge e; int count = 0; for (e = bb->pred; e; e = e->pred_next) count++; bb_ann (bb)->num_preds = count; dfs[bb->index] = BITMAP_XMALLOC (); } for (i = 0; i < num_referenced_vars; i++) var_ann (referenced_var (i))->current_def = NULL; /* Ensure that the dominance information is OK. */ calculate_dominance_info (CDI_DOMINATORS); /* Compute dominance frontiers. */ compute_dominance_frontiers (dfs); /* Setup callbacks for the generic dominator tree walker to find and mark definition sites. */ walk_data.walk_stmts_backward = false; walk_data.dom_direction = CDI_DOMINATORS; walk_data.initialize_block_local_data = NULL; walk_data.before_dom_children_before_stmts = mark_def_sites_initialize_block; walk_data.before_dom_children_walk_stmts = mark_def_sites; walk_data.before_dom_children_after_stmts = NULL; walk_data.after_dom_children_before_stmts = NULL; walk_data.after_dom_children_walk_stmts = NULL; walk_data.after_dom_children_after_stmts = NULL; /* Notice that this bitmap is indexed using variable UIDs, so it must be large enough to accommodate all the variables referenced in the function, not just the ones we are renaming. */ mark_def_sites_global_data.kills = sbitmap_alloc (num_referenced_vars); walk_data.global_data = &mark_def_sites_global_data; /* We do not have any local data. */ walk_data.block_local_data_size = 0; /* Initialize the dominator walker. */ init_walk_dominator_tree (&walk_data); /* Recursively walk the dominator tree. */ walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR); /* Finalize the dominator walker. */ fini_walk_dominator_tree (&walk_data); /* We no longer need this bitmap, clear and free it. */ sbitmap_free (mark_def_sites_global_data.kills); /* Insert PHI nodes at dominance frontiers of definition blocks. */ insert_phi_nodes (dfs); /* Rewrite all the basic blocks in the program. */ timevar_push (TV_TREE_SSA_REWRITE_BLOCKS); /* Setup callbacks for the generic dominator tree walker. */ walk_data.walk_stmts_backward = false; walk_data.dom_direction = CDI_DOMINATORS; walk_data.initialize_block_local_data = rewrite_initialize_block_local_data; walk_data.before_dom_children_before_stmts = rewrite_initialize_block; walk_data.before_dom_children_walk_stmts = rewrite_stmt; walk_data.before_dom_children_after_stmts = rewrite_add_phi_arguments; walk_data.after_dom_children_before_stmts = NULL; walk_data.after_dom_children_walk_stmts = NULL; walk_data.after_dom_children_after_stmts = rewrite_finalize_block; walk_data.global_data = NULL; walk_data.block_local_data_size = sizeof (struct rewrite_block_data); /* Initialize the dominator walker. */ init_walk_dominator_tree (&walk_data); /* Recursively walk the dominator tree rewriting each statement in each basic block. */ walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR); /* Finalize the dominator walker. */ fini_walk_dominator_tree (&walk_data); timevar_pop (TV_TREE_SSA_REWRITE_BLOCKS); /* Debugging dumps. */ if (dump_file && (dump_flags & TDF_STATS)) { dump_dfa_stats (dump_file); dump_tree_ssa_stats (dump_file); } /* Free allocated memory. */ FOR_EACH_BB (bb) BITMAP_XFREE (dfs[bb->index]); free (dfs); htab_delete (def_blocks); timevar_pop (TV_TREE_SSA_OTHER); } struct tree_opt_pass pass_build_ssa = { "ssa", /* name */ NULL, /* gate */ rewrite_into_ssa, /* execute */ NULL, /* sub */ NULL, /* next */ 0, /* static_pass_number */ 0, /* tv_id */ PROP_cfg | PROP_referenced_vars, /* properties_required */ PROP_ssa, /* properties_provided */ 0, /* properties_destroyed */ 0, /* todo_flags_start */ TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */ };