/* Dead store elimination
- Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009
- Free Software Foundation, Inc.
+ Copyright (C) 2004-2014 Free Software Foundation, Inc.
This file is part of GCC.
#include "system.h"
#include "coretypes.h"
#include "tm.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"
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 unsigned int 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,
- gimple_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);
-
-/* Returns uid of statement STMT. */
-
-static unsigned
-get_stmt_uid (gimple stmt)
-{
- if (gimple_code (stmt) == GIMPLE_PHI)
- return SSA_NAME_VERSION (gimple_phi_result (stmt))
- + gimple_stmt_max_uid (cfun);
-
- return gimple_uid (stmt);
-}
-
-/* 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. */
-
-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
- = (struct dse_block_local_data *)
- VEC_last (void_p, walk_data->block_data_stack);
-
- /* 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);
- }
-}
/* A helper of dse_optimize_stmt.
- Given a GIMPLE_ASSIGN in STMT, find a candidate statement *USE_STMT that
- may prove STMT to be dead.
+ 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
-dse_possible_dead_store_p (gimple stmt, gimple *use_stmt)
+dse_possible_dead_store_p (ao_ref *ref, gimple stmt, gimple *use_stmt)
{
gimple temp;
unsigned cnt = 0;
temp = stmt;
do
{
- gimple prev, use_stmt;
+ gimple use_stmt, defvar_def;
imm_use_iterator ui;
bool fail = false;
tree defvar;
defvar = PHI_RESULT (temp);
else
defvar = gimple_vdef (temp);
- prev = 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. */
- if (gimple_code (use_stmt) == GIMPLE_PHI)
+ else if (gimple_code (use_stmt) == GIMPLE_PHI)
{
if (temp
- /* We can look through PHIs to post-dominated regions
- without worrying if the use not also dominates prev
- (in which case it would be a loop PHI with the use
- in a latch block). */
- || gimple_bb (prev) == gimple_bb (use_stmt)
- || !dominated_by_p (CDI_POST_DOMINATORS,
- gimple_bb (prev), gimple_bb (use_stmt))
+ /* Make sure we are not in a loop latch block. */
+ || gimple_bb (stmt) == gimple_bb (use_stmt)
|| dominated_by_p (CDI_DOMINATORS,
- gimple_bb (prev), gimple_bb (use_stmt)))
+ 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);
}
- temp = use_stmt;
+ /* 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,
- gimple_assign_lhs (stmt)))
+ else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
{
fail = true;
BREAK_FROM_IMM_USE_STMT (ui);
just pretend the stmt makes itself dead. Otherwise fail. */
if (!temp)
{
- if (is_hidden_global_store (stmt))
+ if (ref_may_alias_global_p (ref))
return false;
temp = stmt;
break;
}
}
- /* We deliberately stop on clobbering statements and not only on
- killing ones to make walking cheaper. Otherwise we can just
- continue walking until both stores have equal reference trees. */
- while (!stmt_may_clobber_ref_p (temp, gimple_assign_lhs (stmt)));
-
- if (!is_gimple_assign (temp))
- return false;
+ /* Continue walking until we reach a kill. */
+ while (!stmt_kills_ref_p (temp, ref));
*use_stmt = temp;
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,
- gimple_stmt_iterator gsi)
+dse_optimize_stmt (gimple_stmt_iterator *gsi)
{
- struct dse_block_local_data *bd
- = (struct dse_block_local_data *)
- VEC_last (void_p, walk_data->block_data_stack);
- struct dse_global_data *dse_gd
- = (struct dse_global_data *) walk_data->global_data;
- gimple stmt = gsi_stmt (gsi);
+ gimple stmt = gsi_stmt (*gsi);
/* If this statement has no virtual defs, then there is nothing
to do. */
if (!gimple_vdef (stmt))
return;
- /* We know we have virtual definitions. If this is a GIMPLE_ASSIGN
- that's not also a function call, then record it into our table. */
- if (is_gimple_call (stmt) && gimple_call_fndecl (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 (gimple_has_volatile_ops (stmt))
- return;
+ /* We know we have virtual definitions. We can handle assignments and
+ some builtin calls. */
+ if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
+ {
+ 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 (is_gimple_assign (stmt))
{
gimple use_stmt;
- record_voperand_set (dse_gd->stores, &bd->stores, gimple_uid (stmt));
+ /* Self-assignments are zombies. */
+ if (operand_equal_p (gimple_assign_rhs1 (stmt),
+ gimple_assign_lhs (stmt), 0))
+ use_stmt = stmt;
+ else
+ {
+ ao_ref ref;
+ ao_ref_init (&ref, gimple_assign_lhs (stmt));
+ if (!dse_possible_dead_store_p (&ref, stmt, &use_stmt))
+ return;
+ }
+
+ /* Now we know that use_stmt kills the LHS of stmt. */
- if (!dse_possible_dead_store_p (stmt, &use_stmt))
+ /* 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 and the
- stores are to the same memory location or there is a chain of
- virtual uses from stmt and the stmt which stores to that same
- memory location, then we may have found redundant store. */
- if (bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
- && operand_equal_p (gimple_assign_lhs (stmt),
- gimple_assign_lhs (use_stmt), 0))
+ if (dump_file && (dump_flags & TDF_DETAILS))
{
- /* If use_stmt is or might be a nop assignment, e.g. for
- struct { ... } S a, b, *p; ...
- b = a; b = b;
- or
- b = a; b = *p; where p might be &b,
- or
- *p = a; *p = b; where p might be &b,
- or
- *p = *u; *p = *v; where p might be v, then USE_STMT
- acts as a use as well as definition, so store in STMT
- is not dead. */
- if (stmt != use_stmt
- && !is_gimple_reg (gimple_assign_rhs1 (use_stmt))
- && !is_gimple_min_invariant (gimple_assign_rhs1 (use_stmt))
- /* ??? Should {} be invariant? */
- && gimple_assign_rhs_code (use_stmt) != CONSTRUCTOR
- && refs_may_alias_p (gimple_assign_lhs (use_stmt),
- gimple_assign_rhs1 (use_stmt)))
- return;
-
- if (dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, " Deleted dead store '");
- print_gimple_stmt (dump_file, gsi_stmt (gsi), dump_flags, 0);
- fprintf (dump_file, "'\n");
- }
+ fprintf (dump_file, " Deleted dead store '");
+ print_gimple_stmt (dump_file, gsi_stmt (*gsi), dump_flags, 0);
+ fprintf (dump_file, "'\n");
+ }
- /* Then we need to fix the operand of the consuming stmt. */
- unlink_stmt_vdef (stmt);
+ /* Then we need to fix the operand of the consuming stmt. */
+ unlink_stmt_vdef (stmt);
- /* Remove the dead store. */
- gsi_remove (&gsi, true);
+ /* 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);
- }
+ /* 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
+{
+public:
+ dse_dom_walker (cdi_direction direction) : dom_walker (direction) {}
+
+ virtual void before_dom_children (basic_block);
+};
+
+void
+dse_dom_walker::before_dom_children (basic_block bb)
{
- struct dse_block_local_data *bd
- = (struct dse_block_local_data *)
- VEC_last (void_p, walk_data->block_data_stack);
- struct dse_global_data *dse_gd
- = (struct dse_global_data *) walk_data->global_data;
- gimple phi;
gimple_stmt_iterator gsi;
- for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+ for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi);)
{
- phi = gsi_stmt (gsi);
- if (!is_gimple_reg (gimple_phi_result (phi)))
- record_voperand_set (dse_gd->stores, &bd->stores, get_stmt_uid (phi));
+ dse_optimize_stmt (&gsi);
+ if (gsi_end_p (gsi))
+ gsi = gsi_last_bb (bb);
+ else
+ gsi_prev (&gsi);
}
}
-static void
-dse_finalize_block (struct dom_walk_data *walk_data,
- basic_block bb ATTRIBUTE_UNUSED)
+namespace {
+
+const pass_data pass_data_dse =
{
- struct dse_block_local_data *bd
- = (struct dse_block_local_data *)
- VEC_last (void_p, walk_data->block_data_stack);
- struct dse_global_data *dse_gd
- = (struct dse_global_data *) 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_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 */
+};
+
+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 *);
-/* Main entry point. */
+}; // class pass_dse
-static unsigned int
-tree_ssa_dse (void)
+unsigned int
+pass_dse::execute (function *fun)
{
- struct dom_walk_data walk_data;
- struct dse_global_data dse_gd;
+ need_eh_cleanup = BITMAP_ALLOC (NULL);
renumber_gimple_stmt_uids ();
/* 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)
-{
- return flag_tree_dse != 0;
-}
+} // anon namespace
-struct gimple_opt_pass pass_dse =
+gimple_opt_pass *
+make_pass_dse (gcc::context *ctxt)
{
- {
- GIMPLE_PASS,
- "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_verify_ssa /* todo_flags_finish */
- }
-};
-
+ return new pass_dse (ctxt);
+}
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