From df8fe4adb0721ab0e4486bc58482b501fe06287d Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <aldyh@redhat.com>
Date: Mon, 29 Aug 2022 17:52:20 +0200
Subject: [PATCH] A == 0 ? A : -A same as -A (when A is 0.0)
The upcoming work for frange triggers a regression in
gcc.dg/tree-ssa/phi-opt-24.c.
For -O2 -fno-signed-zeros, we fail to transform the following into -A:
float f0(float A)
{
// A == 0? A : -A same as -A
if (A == 0) return A;
return -A;
}
This is because the abs/negative match.pd pattern here:
/* abs/negative simplifications moved from fold_cond_expr_with_comparison,
Need to handle (A - B) case as fold_cond_expr_with_comparison does.
Need to handle UN* comparisons.
...
...
Sees IL that has the 0.0 propagated.
Instead of:
<bb 2> [local count: 1073741824]:
if (A_2(D) == 0.0)
goto <bb 4>; [34.00%]
else
goto <bb 3>; [66.00%]
<bb 3> [local count: 708669601]:
_3 = -A_2(D);
<bb 4> [local count: 1073741824]:
# _1 = PHI <A_2(D)(2), _3(3)>
It now sees:
<bb 4> [local count: 1073741824]:
# _1 = PHI <0.0(2), _3(3)>
which it leaves untouched, causing the if conditional to survive.
Changing integger_zerop to zerop fixes the problem.
I did not include a testcase, as it's just phi-opt-24.c which will get
triggered when I commit the frange with endpoints work.
gcc/ChangeLog:
* match.pd ((cmp @0 zerop) real_zerop (negate@1 @0)): Add variant
for real zero.
---
gcc/match.pd | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/gcc/match.pd b/gcc/match.pd
index 1bb936fc4010..f5fec6342798 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -4804,7 +4804,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(if (!HONOR_SIGNED_ZEROS (type))
@1))
(simplify
- (cnd (cmp @0 zerop) integer_zerop (negate@1 @0))
+ (cnd (cmp @0 zerop) zerop (negate@1 @0))
(if (!HONOR_SIGNED_ZEROS (type))
@1))
)
--
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