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Make ifcvt clean up dead comparisons

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This change is needed to avoid a regression in gcc.dg/ifcvt-3.c
for a later patch.  Without it, we enter CSE with a dead comparison left
by if-conversion and then eliminate the second (live) comparison in
favour of the dead one.  That's functionally correct in itself, but it
meant that we'd combine the subtraction and comparison into a SUBS
before we have a chance to fold away the subtraction.

2019-07-18  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* basic-block.h (CLEANUP_FORCE_FAST_DCE): New macro.
	* cfgcleanup.c (cleanup_cfg): Call run_fast_dce if
	CLEANUP_FORCE_FAST_DCE is set.
	* ifcvt.c (rest_of_handle_if_conversion): Pass
	CLEANUP_FORCE_FAST_DCE to the final cleanup_cfg call if
	if-conversion succeeded.

From-SVN: r273569
This commit is contained in:
Richard Sandiford 2019-07-18 08:24:16 +00:00 • committed by Richard Sandiford
parent d119bf7986
commit f1f1054190
4 changed files with 24 additions and 2 deletions
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9
gcc/ChangeLog
View file

@ -1,3 +1,12 @@
2019-07-18 Richard Sandiford <richard.sandiford@arm.com>
* basic-block.h (CLEANUP_FORCE_FAST_DCE): New macro.
* cfgcleanup.c (cleanup_cfg): Call run_fast_dce if
CLEANUP_FORCE_FAST_DCE is set.
* ifcvt.c (rest_of_handle_if_conversion): Pass
CLEANUP_FORCE_FAST_DCE to the final cleanup_cfg call if
if-conversion succeeded.
2019-07-18 Richard Biener <rguenther@suse.de>
* tree-ssa-sccvn.c (vn_walk_cb_data::push_partial_def): Refactor

2
gcc/basic-block.h
View file

@ -508,6 +508,8 @@ ei_cond (edge_iterator ei, edge *p)
#define CLEANUP_CFGLAYOUT 32 /* Do cleanup in cfglayout mode. */
#define CLEANUP_CFG_CHANGED 64 /* The caller changed the CFG. */
#define CLEANUP_NO_PARTITIONING 128 /* Do not try to fix partitions. */
#define CLEANUP_FORCE_FAST_DCE 0x100 /* Force run_fast_dce to be called
at least once. */
/* Return true if BB is in a transaction. */

8
gcc/cfgcleanup.c
View file

@ -3193,7 +3193,10 @@ cleanup_cfg (int mode)
&& !delete_trivially_dead_insns (get_insns (), max_reg_num ()))
break;
if ((mode & CLEANUP_CROSSJUMP) && crossjumps_occurred)
run_fast_dce ();
{
run_fast_dce ();
mode &= ~CLEANUP_FORCE_FAST_DCE;
}
}
else
break;
@ -3202,6 +3205,9 @@ cleanup_cfg (int mode)
if (mode & CLEANUP_CROSSJUMP)
remove_fake_exit_edges ();
if (mode & CLEANUP_FORCE_FAST_DCE)
run_fast_dce ();
/* Don't call delete_dead_jumptables in cfglayout mode, because
that function assumes that jump tables are in the insns stream.
But we also don't _have_ to delete dead jumptables in cfglayout

7
gcc/ifcvt.c
View file

@ -5457,6 +5457,8 @@ if_convert (bool after_combine)
static unsigned int
rest_of_handle_if_conversion (void)
{
int flags = 0;
if (flag_if_conversion)
{
if (dump_file)
@ -5466,9 +5468,12 @@ rest_of_handle_if_conversion (void)
}
cleanup_cfg (CLEANUP_EXPENSIVE);
if_convert (false);
if (num_updated_if_blocks)
/* Get rid of any dead CC-related instructions. */
flags |= CLEANUP_FORCE_FAST_DCE;
}
cleanup_cfg (0);
cleanup_cfg (flags);
return 0;
}