Hi all,
This is an attempt to solve the problem in the thread starting at
https://gcc.gnu.org/ml/gcc-patches/2015-07/msg01010.html
in a generic way after some pointers from Segher and Andrew.
The problem I got was that combine_simplify_rtx was trying to
do some special handling of unary operations applied to if_then_else
but ended up exiting early due to:
enum rtx_code cond_code = simplify_comparison (NE, &cond, &cop1);
if (cond_code == NE && COMPARISON_P (cond))
return x;
I tried removing that bug that led to regressions in SPEC2006.
The solution that worked for me led to two patches.
In this first patch we add a simplification step to the rtx before trying any
substitutions.
In the second patch I add the simplify-rtx.c simplification to transform - (y ?
-x : x)
into (!y ? -x : x) which fixes the testcase I mentioned in the first thread.
This first patch by itself already showed to be an improvement for aarch64 with
by managing
to eliminate a large amount of redundant zero_extend operations in SPEC2006.
Overall, I saw a 2.8% decrease in [su]xt[bhw] instructions generated for the
whole of SPEC2006
and no regressions in code quality i.e. no instructions that were combined
before but not combine
with this patch.
Bootstrapped and tested on arm, aarch64 and x86_64.
Ok for trunk?
Thanks,
Kyrill
2015-07-16 Kyrylo Tkachov <kyrylo.tkac...@arm.com>
* combine.c (combine_simplify_rtx): Try to simplify if_then_else
rtxes before trying substitutions.
commit 685bc1a66a36292329f678bae555e9c43e434e5d
Author: Kyrylo Tkachov <kyrylo.tkac...@arm.com>
Date: Thu Jul 9 16:54:23 2015 +0100
[combine] Try to simplify before substituting
diff --git a/gcc/combine.c b/gcc/combine.c
index 574f874..40d2231 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -5510,6 +5510,17 @@ combine_simplify_rtx (rtx x, machine_mode op0_mode, int in_dest,
{
rtx cond, true_rtx, false_rtx;
+ /* If some simplification is possible from the start, try it now. */
+ temp = simplify_rtx (x);
+
+ if (temp)
+ {
+ x = temp;
+ code = GET_CODE (x);
+ mode = GET_MODE (x);
+ op0_mode = VOIDmode;
+ }
+
cond = if_then_else_cond (x, &true_rtx, &false_rtx);
if (cond != 0
/* If everything is a comparison, what we have is highly unlikely
