https://bugs.llvm.org/show_bug.cgi?id=43223
Bug ID: 43223
Summary: When -ffp-contract=on is effective, fma conversion
works even with -O0.
Product: new-bugs
Version: unspecified
Hardware: Other
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: ueno.masak...@jp.fujitsu.com
CC: htmldevelo...@gmail.com, llvm-bugs@lists.llvm.org
When -ffp-contract=on is effective, fma conversion works even with -O0.
I think it is better to stop fma conversion when -O0.
Sample program:
float foo(float b, float c, float d) {
return b * c + d;
}
$ clang -O0 -ffp-contract=on a.c -S -o - | grep fma // OK?
fmadd s0, s0, s1, s2
$ clang -O1 -ffp-contract=on a.c -S -o - | grep fma
fmadd s0, s0, s1, s2
$ clang -O0 -ffp-contract=fast a.c -S -o - | grep fma
$ clang -O1 -ffp-contract=fast a.c -S -o - | grep fma
fmadd s0, s0, s1, s2
It seems that it can be stopped by making the following changes.
What do you think?
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp
b/clang/lib/CodeGen/CGExprScalar.cpp
index 3d082de..f0d9fda 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -3308,7 +3308,8 @@ static Value* tryEmitFMulAdd(const BinOpInfo &op,
"Only fadd/fsub can be the root of an fmuladd.");
// Check whether this op is marked as fusable.
- if (!op.FPFeatures.allowFPContractWithinStatement())
+ if (CGF.CGM.getCodeGenOpts().OptimizationLevel == 0 ||
+ !op.FPFeatures.allowFPContractWithinStatement())
return nullptr;
// We have a potentially fusable op. Look for a mul on one of the operands.
--
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