/* Dead store elimination
- Copyright (C) 2004-2013 Free Software Foundation, Inc.
+ Copyright (C) 2004-2017 Free Software Foundation, Inc.
This file is part of GCC.
#include "config.h"
#include "system.h"
#include "coretypes.h"
-#include "tm.h"
-#include "ggc.h"
+#include "backend.h"
+#include "rtl.h"
#include "tree.h"
-#include "tm_p.h"
-#include "basic-block.h"
-#include "gimple-pretty-print.h"
-#include "bitmap.h"
#include "gimple.h"
+#include "tree-pass.h"
+#include "ssa.h"
+#include "gimple-pretty-print.h"
+#include "fold-const.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 "domwalk.h"
-#include "flags.h"
-#include "langhooks.h"
#include "tree-cfgcleanup.h"
/* This file implements dead store elimination.
remove their dead edges eventually. */
static bitmap need_eh_cleanup;
-static bool gate_dse (void);
-static unsigned int tree_ssa_dse (void);
-
/* 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;
+ gimple *temp;
unsigned cnt = 0;
*use_stmt = NULL;
- /* Self-assignments are zombies. */
- if (operand_equal_p (gimple_assign_rhs1 (stmt), gimple_assign_lhs (stmt), 0))
- {
- *use_stmt = stmt;
- return true;
- }
-
/* 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
temp = stmt;
do
{
- gimple use_stmt, defvar_def;
+ gimple *use_stmt, *defvar_def;
imm_use_iterator ui;
bool fail = false;
tree defvar;
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 (stmt_may_clobber_global_p (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)));
+ /* Continue walking until we reach a kill. */
+ while (!stmt_kills_ref_p (temp, ref));
*use_stmt = temp;
static void
dse_optimize_stmt (gimple_stmt_iterator *gsi)
{
- 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))
- return;
-
/* 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;
+ /* 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);
+ release_defs (stmt);
+ }
+ break;
+ }
+ default:
+ return;
+ }
+ }
+
if (is_gimple_assign (stmt))
{
- gimple use_stmt;
+ gimple *use_stmt;
- if (!dse_possible_dead_store_p (stmt, &use_stmt))
- return;
+ /* 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. */
/* But only remove *this_2(D) ={v} {CLOBBER} if killed by
another clobber 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 ((gimple_has_lhs (use_stmt)
- && (operand_equal_p (gimple_assign_lhs (stmt),
- gimple_get_lhs (use_stmt), 0)))
- || stmt_kills_ref_p (use_stmt, gimple_assign_lhs (stmt)))
+ if (dump_file && (dump_flags & TDF_DETAILS))
{
- basic_block bb;
-
- /* 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
- && ref_maybe_used_by_stmt_p (use_stmt, gimple_assign_lhs (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. */
- bb = gimple_bb (stmt);
- if (gsi_remove (gsi, true))
- bitmap_set_bit (need_eh_cleanup, bb->index);
+ /* 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);
}
}
public:
dse_dom_walker (cdi_direction direction) : dom_walker (direction) {}
- virtual void before_dom_children (basic_block);
+ virtual edge before_dom_children (basic_block);
};
-void
+edge
dse_dom_walker::before_dom_children (basic_block bb)
{
gimple_stmt_iterator gsi;
else
gsi_prev (&gsi);
}
+ return NULL;
}
-/* Main entry point. */
+namespace {
-static unsigned int
-tree_ssa_dse (void)
+const pass_data pass_data_dse =
+{
+ 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 *);
+
+}; // class pass_dse
+
+unsigned int
+pass_dse::execute (function *fun)
{
need_eh_cleanup = BITMAP_ALLOC (NULL);
/* Dead store elimination is fundamentally a walk of the post-dominator
tree and a backwards walk of statements within each block. */
- dse_dom_walker (CDI_POST_DOMINATORS).walk (cfun->cfg->x_exit_block_ptr);
+ dse_dom_walker (CDI_POST_DOMINATORS).walk (fun->cfg->x_exit_block_ptr);
/* Removal of stores may make some EH edges dead. Purge such edges from
the CFG as needed. */
return 0;
}
-static bool
-gate_dse (void)
-{
- return flag_tree_dse != 0;
-}
-
-namespace {
-
-const pass_data pass_data_dse =
-{
- GIMPLE_PASS, /* type */
- "dse", /* name */
- OPTGROUP_NONE, /* optinfo_flags */
- true, /* has_gate */
- true, /* has_execute */
- TV_TREE_DSE, /* tv_id */
- ( PROP_cfg | PROP_ssa ), /* properties_required */
- 0, /* properties_provided */
- 0, /* properties_destroyed */
- 0, /* todo_flags_start */
- TODO_verify_ssa, /* 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); }
- bool gate () { return gate_dse (); }
- unsigned int execute () { return tree_ssa_dse (); }
-
-}; // class pass_dse
-
} // anon namespace
gimple_opt_pass *
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