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.
Tested on aarch64-linux-gnu, aarch64_be-elf and x86_64-linux-gnu.
OK to install?
Richard
2019-07-11 Richard Sandiford <richard.sandif...@arm.com>
gcc/
* ifcvt.c: Include dce.h.
(if_convert): Call run_fast_dce if the pass changed something.
Index: gcc/ifcvt.c
===================================================================
--- gcc/ifcvt.c 2019-03-08 18:15:26.828777872 +0000
+++ gcc/ifcvt.c 2019-07-12 08:58:21.787403345 +0100
@@ -46,6 +46,7 @@
#include "rtl-iter.h"
#include "ifcvt.h"
#include "params.h"
+#include "dce.h"
#ifndef MAX_CONDITIONAL_EXECUTE
#define MAX_CONDITIONAL_EXECUTE \
@@ -5443,6 +5444,10 @@ if_convert (bool after_combine)
num_true_changes);
}
+ if (num_updated_if_blocks)
+ /* Get rid of any dead CC-related instructions. */
+ run_fast_dce ();
+
if (optimize == 1)
df_remove_problem (df_live);
