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.
Adding a variant to the pattern that for real_zerop fixes the problem.
I am a match.pd weenie, and am avoiding touching more patterns that
may also benefit from handling real constants. So please use simple
words if what I'm doing isn't correct ;-).
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.
Tested on x86-64 & ppc64le Linux.
OK?
gcc/ChangeLog:
* match.pd ((cmp @0 zerop) real_zerop (negate@1 @0)): Add variant
for real zero.
---
gcc/match.pd | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/gcc/match.pd b/gcc/match.pd
index 1bb936fc401..5bdea300f94 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -4803,6 +4803,10 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(cnd (cmp @0 zerop) @0 (negate@1 @0))
(if (!HONOR_SIGNED_ZEROS (type))
@1))
+ (simplify
+ (cnd (cmp @0 zerop) real_zerop (negate@1 @0))
+ (if (!HONOR_SIGNED_ZEROS (type))
+ @1))
(simplify
(cnd (cmp @0 zerop) integer_zerop (negate@1 @0))
(if (!HONOR_SIGNED_ZEROS (type))
--
2.37.1
