/* Dead store elimination
- Copyright (C) 2004, 2005 Free Software Foundation, Inc.
+ Copyright (C) 2004-2014 Free Software Foundation, Inc.
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)
+the Free Software Foundation; either version 3, or (at your option)
any later version.
GCC is distributed in the hope that it will be useful,
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. */
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
-#include "errors.h"
-#include "ggc.h"
#include "tree.h"
-#include "rtl.h"
#include "tm_p.h"
+#include "predict.h"
+#include "vec.h"
+#include "hashtab.h"
+#include "hash-set.h"
+#include "machmode.h"
+#include "hard-reg-set.h"
+#include "input.h"
+#include "function.h"
+#include "dominance.h"
+#include "cfg.h"
#include "basic-block.h"
-#include "timevar.h"
-#include "diagnostic.h"
-#include "tree-flow.h"
+#include "gimple-pretty-print.h"
+#include "bitmap.h"
+#include "tree-ssa-alias.h"
+#include "internal-fn.h"
+#include "gimple-expr.h"
+#include "is-a.h"
+#include "gimple.h"
+#include "gimple-iterator.h"
+#include "gimple-ssa.h"
+#include "tree-cfg.h"
+#include "tree-phinodes.h"
+#include "ssa-iterators.h"
+#include "stringpool.h"
+#include "tree-ssanames.h"
+#include "expr.h"
+#include "tree-dfa.h"
#include "tree-pass.h"
-#include "tree-dump.h"
#include "domwalk.h"
#include "flags.h"
+#include "langhooks.h"
+#include "tree-cfgcleanup.h"
/* This file implements dead store elimination.
In our SSA + virtual operand world we use immediate uses of virtual
operands to detect dead stores. If a store's virtual definition
is used precisely once by a later store to the same location which
- post dominates the first store, then the first store is dead.
+ post dominates the first store, then the first store is dead.
The single use of the store's virtual definition ensures that
there are no intervening aliased loads and the requirement that
It may help to think of this as first moving the earlier store to
the point immediately before the later store. Again, the single
use of the virtual definition and the post-dominance relationship
- ensure that such movement would be safe. Clearly if there are
+ ensure that such movement would be safe. Clearly if there are
back to back stores, then the second is redundant.
Reviewing section 10.7.2 in Morgan's "Building an Optimizing Compiler"
relationship between dead store and redundant load elimination. In
fact, they are the same transformation applied to different views of
the CFG. */
-
-struct dse_global_data
-{
- /* This is the global bitmap for store statements.
- Each statement has a unique ID. When we encounter a store statement
- that we want to record, set the bit corresponding to the statement's
- unique ID in this bitmap. */
- bitmap stores;
-};
+/* Bitmap of blocks that have had EH statements cleaned. We should
+ remove their dead edges eventually. */
+static bitmap need_eh_cleanup;
-/* We allocate a bitmap-per-block for stores which are encountered
- during the scan of that block. This allows us to restore the
- global bitmap of stores when we finish processing a block. */
-struct dse_block_local_data
-{
- bitmap stores;
-};
-static bool gate_dse (void);
-static void tree_ssa_dse (void);
-static void dse_initialize_block_local_data (struct dom_walk_data *,
- basic_block,
- bool);
-static void dse_optimize_stmt (struct dom_walk_data *,
- basic_block,
- block_stmt_iterator);
-static void dse_record_phis (struct dom_walk_data *, basic_block);
-static void dse_finalize_block (struct dom_walk_data *, basic_block);
-static void record_voperand_set (bitmap, bitmap *, unsigned int);
-
-static unsigned max_stmt_uid; /* Maximal uid of a statement. Uids to phi
- nodes are assigned using the versions of
- ssa names they define. */
-
-/* Returns uid of statement STMT. */
-
-static unsigned
-get_stmt_uid (tree stmt)
-{
- if (TREE_CODE (stmt) == PHI_NODE)
- return SSA_NAME_VERSION (PHI_RESULT (stmt)) + max_stmt_uid;
-
- return stmt_ann (stmt)->uid;
-}
-
-/* Function indicating whether we ought to include information for 'var'
- when calculating immediate uses. For this pass we only want use
- information for virtual variables. */
+/* A helper of dse_optimize_stmt.
+ Given a GIMPLE_ASSIGN in STMT that writes to REF, find a candidate
+ statement *USE_STMT that may prove STMT to be dead.
+ Return TRUE if the above conditions are met, otherwise FALSE. */
static bool
-need_imm_uses_for (tree var)
+dse_possible_dead_store_p (ao_ref *ref, gimple stmt, gimple *use_stmt)
{
- return !is_gimple_reg (var);
-}
+ gimple temp;
+ unsigned cnt = 0;
+ *use_stmt = NULL;
-/* Set bit UID in bitmaps GLOBAL and *LOCAL, creating *LOCAL as needed. */
-static void
-record_voperand_set (bitmap global, bitmap *local, unsigned int uid)
-{
- /* Lazily allocate the bitmap. Note that we do not get a notification
- when the block local data structures die, so we allocate the local
- bitmap backed by the GC system. */
- if (*local == NULL)
- *local = BITMAP_GGC_ALLOC ();
-
- /* Set the bit in the local and global bitmaps. */
- bitmap_set_bit (*local, uid);
- bitmap_set_bit (global, uid);
-}
-/* Initialize block local data structures. */
+ /* Find the first dominated statement that clobbers (part of) the
+ memory stmt stores to with no intermediate statement that may use
+ part of the memory stmt stores. That is, find a store that may
+ prove stmt to be a dead store. */
+ temp = stmt;
+ do
+ {
+ gimple use_stmt, defvar_def;
+ imm_use_iterator ui;
+ bool fail = false;
+ tree defvar;
+
+ /* Limit stmt walking to be linear in the number of possibly
+ dead stores. */
+ if (++cnt > 256)
+ return false;
+
+ if (gimple_code (temp) == GIMPLE_PHI)
+ defvar = PHI_RESULT (temp);
+ else
+ defvar = gimple_vdef (temp);
+ defvar_def = temp;
+ temp = NULL;
+ FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
+ {
+ cnt++;
+
+ /* If we ever reach our DSE candidate stmt again fail. We
+ cannot handle dead stores in loops. */
+ if (use_stmt == stmt)
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ /* In simple cases we can look through PHI nodes, but we
+ have to be careful with loops and with memory references
+ containing operands that are also operands of PHI nodes.
+ See gcc.c-torture/execute/20051110-*.c. */
+ else if (gimple_code (use_stmt) == GIMPLE_PHI)
+ {
+ if (temp
+ /* Make sure we are not in a loop latch block. */
+ || gimple_bb (stmt) == gimple_bb (use_stmt)
+ || dominated_by_p (CDI_DOMINATORS,
+ gimple_bb (stmt), gimple_bb (use_stmt))
+ /* We can look through PHIs to regions post-dominating
+ the DSE candidate stmt. */
+ || !dominated_by_p (CDI_POST_DOMINATORS,
+ gimple_bb (stmt), gimple_bb (use_stmt)))
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ /* Do not consider the PHI as use if it dominates the
+ stmt defining the virtual operand we are processing,
+ we have processed it already in this case. */
+ if (gimple_bb (defvar_def) != gimple_bb (use_stmt)
+ && !dominated_by_p (CDI_DOMINATORS,
+ gimple_bb (defvar_def),
+ gimple_bb (use_stmt)))
+ temp = use_stmt;
+ }
+ /* If the statement is a use the store is not dead. */
+ else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ /* If this is a store, remember it or bail out if we have
+ multiple ones (the will be in different CFG parts then). */
+ else if (gimple_vdef (use_stmt))
+ {
+ if (temp)
+ {
+ fail = true;
+ BREAK_FROM_IMM_USE_STMT (ui);
+ }
+ temp = use_stmt;
+ }
+ }
-static void
-dse_initialize_block_local_data (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED,
- bool recycled)
-{
- struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack);
+ if (fail)
+ return false;
- /* If we are given a recycled block local data structure, ensure any
- bitmap associated with the block is cleared. */
- if (recycled)
- {
- if (bd->stores)
- bitmap_clear (bd->stores);
+ /* If we didn't find any definition this means the store is dead
+ if it isn't a store to global reachable memory. In this case
+ just pretend the stmt makes itself dead. Otherwise fail. */
+ if (!temp)
+ {
+ if (ref_may_alias_global_p (ref))
+ return false;
+
+ temp = stmt;
+ break;
+ }
}
+ /* Continue walking until we reach a kill. */
+ while (!stmt_kills_ref_p (temp, ref));
+
+ *use_stmt = temp;
+
+ return true;
}
+
/* Attempt to eliminate dead stores in the statement referenced by BSI.
A dead store is a store into a memory location which will later be
post dominates the first store, then the first store is dead. */
static void
-dse_optimize_stmt (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED,
- block_stmt_iterator bsi)
+dse_optimize_stmt (gimple_stmt_iterator *gsi)
{
- struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack);
- struct dse_global_data *dse_gd = walk_data->global_data;
- tree stmt = bsi_stmt (bsi);
- stmt_ann_t ann = stmt_ann (stmt);
- v_may_def_optype v_may_defs;
-
- get_stmt_operands (stmt);
- v_may_defs = V_MAY_DEF_OPS (ann);
+ gimple stmt = gsi_stmt (*gsi);
/* If this statement has no virtual defs, then there is nothing
to do. */
- if (NUM_V_MAY_DEFS (v_may_defs) == 0)
+ if (!gimple_vdef (stmt))
return;
- /* We know we have virtual definitions. If this is a MODIFY_EXPR that's
- not also a function call, then record it into our table. */
- if (get_call_expr_in (stmt))
+ /* Don't return early on *this_2(D) ={v} {CLOBBER}. */
+ if (gimple_has_volatile_ops (stmt)
+ && (!gimple_clobber_p (stmt)
+ || TREE_CODE (gimple_assign_lhs (stmt)) != MEM_REF))
return;
- if (ann->has_volatile_ops)
- return;
-
- if (TREE_CODE (stmt) == MODIFY_EXPR)
+ /* We know we have virtual definitions. We can handle assignments and
+ some builtin calls. */
+ if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
{
- unsigned int num_uses = 0, count = 0;
- use_operand_p first_use_p = NULL_USE_OPERAND_P;
- use_operand_p use_p;
- tree use, use_stmt;
- tree defvar = NULL_TREE, usevar = NULL_TREE;
- use_operand_p var2;
- def_operand_p var1;
- ssa_op_iter op_iter;
-
- FOR_EACH_SSA_MAYDEF_OPERAND (var1, var2, stmt, op_iter)
- {
- defvar = DEF_FROM_PTR (var1);
- usevar = USE_FROM_PTR (var2);
- num_uses += num_imm_uses (defvar);
- count++;
- if (num_uses > 1 || count > 1)
- break;
+ switch (DECL_FUNCTION_CODE (gimple_call_fndecl (stmt)))
+ {
+ case BUILT_IN_MEMCPY:
+ case BUILT_IN_MEMMOVE:
+ case BUILT_IN_MEMSET:
+ {
+ gimple use_stmt;
+ ao_ref ref;
+ tree size = NULL_TREE;
+ if (gimple_call_num_args (stmt) == 3)
+ size = gimple_call_arg (stmt, 2);
+ tree ptr = gimple_call_arg (stmt, 0);
+ ao_ref_init_from_ptr_and_size (&ref, ptr, size);
+ if (!dse_possible_dead_store_p (&ref, stmt, &use_stmt))
+ return;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, " Deleted dead call '");
+ print_gimple_stmt (dump_file, gsi_stmt (*gsi), dump_flags, 0);
+ fprintf (dump_file, "'\n");
+ }
+
+ tree lhs = gimple_call_lhs (stmt);
+ if (lhs)
+ {
+ gimple new_stmt = gimple_build_assign (lhs, ptr);
+ unlink_stmt_vdef (stmt);
+ if (gsi_replace (gsi, new_stmt, true))
+ bitmap_set_bit (need_eh_cleanup, gimple_bb (stmt)->index);
+ }
+ else
+ {
+ /* Then we need to fix the operand of the consuming stmt. */
+ unlink_stmt_vdef (stmt);
+
+ /* Remove the dead store. */
+ if (gsi_remove (gsi, true))
+ bitmap_set_bit (need_eh_cleanup, gimple_bb (stmt)->index);
+ }
+ break;
+ }
+ default:
+ return;
}
+ }
- if (count == 1 && num_uses == 1)
- {
- single_imm_use (defvar, &use_p, &use_stmt);
- gcc_assert (use_p != NULL_USE_OPERAND_P);
- first_use_p = use_p;
- use = USE_FROM_PTR (use_p);
- }
+ if (is_gimple_assign (stmt))
+ {
+ gimple use_stmt;
+
+ /* Self-assignments are zombies. */
+ if (operand_equal_p (gimple_assign_rhs1 (stmt),
+ gimple_assign_lhs (stmt), 0))
+ use_stmt = stmt;
else
{
- record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
- return;
+ ao_ref ref;
+ ao_ref_init (&ref, gimple_assign_lhs (stmt));
+ if (!dse_possible_dead_store_p (&ref, stmt, &use_stmt))
+ return;
}
- /* Skip through any PHI nodes we have already seen if the PHI
- represents the only use of this store.
+ /* Now we know that use_stmt kills the LHS of stmt. */
- Note this does not handle the case where the store has
- multiple V_MAY_DEFs which all reach a set of PHI nodes in the
- same block. */
- while (use_p != NULL_USE_OPERAND_P
- && TREE_CODE (use_stmt) == PHI_NODE
- && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt)))
- {
- /* Skip past this PHI and loop again in case we had a PHI
- chain. */
- if (single_imm_use (PHI_RESULT (use_stmt), &use_p, &use_stmt))
- use = USE_FROM_PTR (use_p);
- }
+ /* But only remove *this_2(D) ={v} {CLOBBER} if killed by
+ another clobber stmt. */
+ if (gimple_clobber_p (stmt)
+ && !gimple_clobber_p (use_stmt))
+ return;
- /* If we have precisely one immediate use at this point, then we may
- have found redundant store. */
- if (use_p != NULL_USE_OPERAND_P
- && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
- && operand_equal_p (TREE_OPERAND (stmt, 0),
- TREE_OPERAND (use_stmt, 0), 0))
+ if (dump_file && (dump_flags & TDF_DETAILS))
{
- tree def;
- ssa_op_iter iter;
-
- /* Make sure we propagate the ABNORMAL bit setting. */
- if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (USE_FROM_PTR (first_use_p)))
- SSA_NAME_OCCURS_IN_ABNORMAL_PHI (usevar) = 1;
- /* Then we need to fix the operand of the consuming stmt. */
- SET_USE (first_use_p, usevar);
-
- if (dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, " Deleted dead store '");
- print_generic_expr (dump_file, bsi_stmt (bsi), dump_flags);
- fprintf (dump_file, "'\n");
- }
-
- /* Remove the dead store. */
- bsi_remove (&bsi);
-
- /* The virtual defs for the dead statement will need to be
- updated. Since these names are going to disappear,
- FUD chains for uses downstream need to be updated. */
- FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_VIRTUAL_DEFS)
- mark_sym_for_renaming (SSA_NAME_VAR (def));
-
- /* And release any SSA_NAMEs set in this statement back to the
- SSA_NAME manager. */
- release_defs (stmt);
+ fprintf (dump_file, " Deleted dead store '");
+ print_gimple_stmt (dump_file, gsi_stmt (*gsi), dump_flags, 0);
+ fprintf (dump_file, "'\n");
}
- record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
+ /* Then we need to fix the operand of the consuming stmt. */
+ unlink_stmt_vdef (stmt);
+
+ /* Remove the dead store. */
+ basic_block bb = gimple_bb (stmt);
+ if (gsi_remove (gsi, true))
+ bitmap_set_bit (need_eh_cleanup, bb->index);
+
+ /* And release any SSA_NAMEs set in this statement back to the
+ SSA_NAME manager. */
+ release_defs (stmt);
}
}
-/* Record that we have seen the PHIs at the start of BB which correspond
- to virtual operands. */
-static void
-dse_record_phis (struct dom_walk_data *walk_data, basic_block bb)
+class dse_dom_walker : public dom_walker
{
- struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack);
- struct dse_global_data *dse_gd = walk_data->global_data;
- tree phi;
-
- for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
- if (need_imm_uses_for (PHI_RESULT (phi)))
- record_voperand_set (dse_gd->stores,
- &bd->stores,
- get_stmt_uid (phi));
-}
+public:
+ dse_dom_walker (cdi_direction direction) : dom_walker (direction) {}
-static void
-dse_finalize_block (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED)
+ virtual void before_dom_children (basic_block);
+};
+
+void
+dse_dom_walker::before_dom_children (basic_block bb)
{
- struct dse_block_local_data *bd
- = VARRAY_TOP_GENERIC_PTR (walk_data->block_data_stack);
- struct dse_global_data *dse_gd = walk_data->global_data;
- bitmap stores = dse_gd->stores;
- unsigned int i;
- bitmap_iterator bi;
-
- /* Unwind the stores noted in this basic block. */
- if (bd->stores)
- EXECUTE_IF_SET_IN_BITMAP (bd->stores, 0, i, bi)
- {
- bitmap_clear_bit (stores, i);
- }
+ gimple_stmt_iterator gsi;
+
+ for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi);)
+ {
+ dse_optimize_stmt (&gsi);
+ if (gsi_end_p (gsi))
+ gsi = gsi_last_bb (bb);
+ else
+ gsi_prev (&gsi);
+ }
}
-static void
-tree_ssa_dse (void)
+namespace {
+
+const pass_data pass_data_dse =
{
- struct dom_walk_data walk_data;
- struct dse_global_data dse_gd;
- basic_block bb;
-
- /* Create a UID for each statement in the function. Ordering of the
- UIDs is not important for this pass. */
- max_stmt_uid = 0;
- FOR_EACH_BB (bb)
- {
- block_stmt_iterator bsi;
+ GIMPLE_PASS, /* type */
+ "dse", /* name */
+ OPTGROUP_NONE, /* optinfo_flags */
+ TV_TREE_DSE, /* tv_id */
+ ( PROP_cfg | PROP_ssa ), /* properties_required */
+ 0, /* properties_provided */
+ 0, /* properties_destroyed */
+ 0, /* todo_flags_start */
+ 0, /* todo_flags_finish */
+};
- for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
- stmt_ann (bsi_stmt (bsi))->uid = max_stmt_uid++;
- }
+class pass_dse : public gimple_opt_pass
+{
+public:
+ pass_dse (gcc::context *ctxt)
+ : gimple_opt_pass (pass_data_dse, ctxt)
+ {}
+
+ /* opt_pass methods: */
+ opt_pass * clone () { return new pass_dse (m_ctxt); }
+ virtual bool gate (function *) { return flag_tree_dse != 0; }
+ virtual unsigned int execute (function *);
+
+}; // class pass_dse
+
+unsigned int
+pass_dse::execute (function *fun)
+{
+ need_eh_cleanup = BITMAP_ALLOC (NULL);
+
+ renumber_gimple_stmt_uids ();
/* We might consider making this a property of each pass so that it
can be [re]computed on an as-needed basis. Particularly since
this pass could be seen as an extension of DCE which needs post
dominators. */
calculate_dominance_info (CDI_POST_DOMINATORS);
+ calculate_dominance_info (CDI_DOMINATORS);
/* Dead store elimination is fundamentally a walk of the post-dominator
tree and a backwards walk of statements within each block. */
- walk_data.walk_stmts_backward = true;
- walk_data.dom_direction = CDI_POST_DOMINATORS;
- walk_data.initialize_block_local_data = dse_initialize_block_local_data;
- walk_data.before_dom_children_before_stmts = NULL;
- walk_data.before_dom_children_walk_stmts = dse_optimize_stmt;
- walk_data.before_dom_children_after_stmts = dse_record_phis;
- walk_data.after_dom_children_before_stmts = NULL;
- walk_data.after_dom_children_walk_stmts = NULL;
- walk_data.after_dom_children_after_stmts = dse_finalize_block;
- walk_data.interesting_blocks = NULL;
-
- walk_data.block_local_data_size = sizeof (struct dse_block_local_data);
-
- /* This is the main hash table for the dead store elimination pass. */
- dse_gd.stores = BITMAP_ALLOC (NULL);
- walk_data.global_data = &dse_gd;
-
- /* Initialize the dominator walker. */
- init_walk_dominator_tree (&walk_data);
+ dse_dom_walker (CDI_POST_DOMINATORS).walk (fun->cfg->x_exit_block_ptr);
- /* Recursively walk the dominator tree. */
- walk_dominator_tree (&walk_data, EXIT_BLOCK_PTR);
-
- /* Finalize the dominator walker. */
- fini_walk_dominator_tree (&walk_data);
-
- /* Release the main bitmap. */
- BITMAP_FREE (dse_gd.stores);
+ /* Removal of stores may make some EH edges dead. Purge such edges from
+ the CFG as needed. */
+ if (!bitmap_empty_p (need_eh_cleanup))
+ {
+ gimple_purge_all_dead_eh_edges (need_eh_cleanup);
+ cleanup_tree_cfg ();
+ }
+ BITMAP_FREE (need_eh_cleanup);
+
/* For now, just wipe the post-dominator information. */
free_dominance_info (CDI_POST_DOMINATORS);
+ return 0;
}
-static bool
-gate_dse (void)
+} // anon namespace
+
+gimple_opt_pass *
+make_pass_dse (gcc::context *ctxt)
{
- return flag_tree_dse != 0;
+ return new pass_dse (ctxt);
}
-
-struct tree_opt_pass pass_dse = {
- "dse", /* name */
- gate_dse, /* gate */
- tree_ssa_dse, /* execute */
- NULL, /* sub */
- NULL, /* next */
- 0, /* static_pass_number */
- TV_TREE_DSE, /* tv_id */
- PROP_cfg
- | PROP_ssa
- | PROP_alias, /* properties_required */
- 0, /* properties_provided */
- 0, /* properties_destroyed */
- 0, /* todo_flags_start */
- TODO_dump_func
- | TODO_ggc_collect
- | TODO_update_ssa
- | TODO_verify_ssa, /* todo_flags_finish */
- 0 /* letter */
-};
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