I have tested the following patch to remove (where easy) dead code
in the way of sinking.
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2017-04-24 Richard Biener <rguent...@suse.de>
PR tree-optimization/79725
* tree-ssa-sink.c (statement_sink_location): Return whether
failure reason was zero uses. Move that check later.
(sink_code_in_bb): Deal with zero uses by removing the stmt
if possible.
* gcc.dg/tree-ssa/ssa-sink-15.c: New testcase.
Index: gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-15.c
===================================================================
*** gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-15.c (nonexistent)
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-15.c (working copy)
***************
*** 0 ****
--- 1,14 ----
+ /* PR79725 */
+ /* { dg-do compile } */
+ /* { dg-options "-O2 -fdump-tree-optimized" } */
+
+ _Complex double f(_Complex double x[])
+ {
+ _Complex float p = 1.0;
+ for (int i = 0; i < 1000000; i++)
+ p = x[i];
+ return p;
+ }
+
+ /* Verify we end up with a single BB and no loop. */
+ /* { dg-final { scan-tree-dump-times "goto" 0 "optimized" } } */
Index: gcc/tree-ssa-sink.c
===================================================================
--- gcc/tree-ssa-sink.c (revision 247060)
+++ gcc/tree-ssa-sink.c (working copy)
@@ -244,7 +244,7 @@ select_best_block (basic_block early_bb,
static bool
statement_sink_location (gimple *stmt, basic_block frombb,
- gimple_stmt_iterator *togsi)
+ gimple_stmt_iterator *togsi, bool *zero_uses_p)
{
gimple *use;
use_operand_p one_use = NULL_USE_OPERAND_P;
@@ -254,6 +254,8 @@ statement_sink_location (gimple *stmt, b
ssa_op_iter iter;
imm_use_iterator imm_iter;
+ *zero_uses_p = false;
+
/* We only can sink assignments. */
if (!is_gimple_assign (stmt))
return false;
@@ -263,10 +265,6 @@ statement_sink_location (gimple *stmt, b
if (def_p == NULL_DEF_OPERAND_P)
return false;
- /* Return if there are no immediate uses of this stmt. */
- if (has_zero_uses (DEF_FROM_PTR (def_p)))
- return false;
-
/* There are a few classes of things we can't or don't move, some because we
don't have code to handle it, some because it's not profitable and some
because it's not legal.
@@ -292,11 +290,17 @@ statement_sink_location (gimple *stmt, b
*/
if (stmt_ends_bb_p (stmt)
|| gimple_has_side_effects (stmt)
- || gimple_has_volatile_ops (stmt)
|| (cfun->has_local_explicit_reg_vars
&& TYPE_MODE (TREE_TYPE (gimple_assign_lhs (stmt))) == BLKmode))
return false;
+ /* Return if there are no immediate uses of this stmt. */
+ if (has_zero_uses (DEF_FROM_PTR (def_p)))
+ {
+ *zero_uses_p = true;
+ return false;
+ }
+
if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (DEF_FROM_PTR (def_p)))
return false;
@@ -483,12 +487,23 @@ sink_code_in_bb (basic_block bb)
{
gimple *stmt = gsi_stmt (gsi);
gimple_stmt_iterator togsi;
+ bool zero_uses_p;
- if (!statement_sink_location (stmt, bb, &togsi))
+ if (!statement_sink_location (stmt, bb, &togsi, &zero_uses_p))
{
+ gimple_stmt_iterator saved = gsi;
if (!gsi_end_p (gsi))
gsi_prev (&gsi);
- last = false;
+ /* If we face a dead stmt remove it as it possibly blocks
+ sinking of uses. */
+ if (zero_uses_p
+ && ! gimple_vdef (stmt))
+ {
+ gsi_remove (&saved, true);
+ release_defs (stmt);
+ }
+ else
+ last = false;
continue;
}
if (dump_file)
