[LibCallSimplifier] use instruction-level fast-math-flags to transform sqrt calls
This is a continuation of adding FMF to call instructions:
http://reviews.llvm.org/rL255555
The intent of the patch is to preserve the current behavior of the transform except
that we use the sqrt instruction's 'fast' attribute as a trigger rather than the
function-level attribute.
But this raises a bug noted by the new FIXME comment.
In order to do this transform:
sqrt((x * x) * y) ---> fabs(x) * sqrt(y)
...we need all of the sqrt, the first fmul, and the second fmul to be 'fast'.
If any of those ops is strict, we should bail out.
Differential Revision: http://reviews.llvm.org/D15937
llvm-svn: 257400
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index edf0db4..cf87ac1 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1397,7 +1397,8 @@
if (TLI->has(LibFunc::sqrtf) && (Callee->getName() == "sqrt" ||
Callee->getIntrinsicID() == Intrinsic::sqrt))
Ret = optimizeUnaryDoubleFP(CI, B, true);
- if (!canUseUnsafeFPMath(CI->getParent()->getParent()))
+
+ if (!CI->hasUnsafeAlgebra())
return Ret;
Instruction *I = dyn_cast<Instruction>(CI->getArgOperand(0));
@@ -1406,7 +1407,7 @@
// We're looking for a repeated factor in a multiplication tree,
// so we can do this fold: sqrt(x * x) -> fabs(x);
- // or this fold: sqrt(x * x * y) -> fabs(x) * sqrt(y).
+ // or this fold: sqrt((x * x) * y) -> fabs(x) * sqrt(y).
Value *Op0 = I->getOperand(0);
Value *Op1 = I->getOperand(1);
Value *RepeatOp = nullptr;
@@ -1421,6 +1422,7 @@
// variations of this pattern because instcombine's visitFMUL and/or the
// reassociation pass should give us this form.
Value *OtherMul0, *OtherMul1;
+ // FIXME: This multiply must be unsafe to allow this transform.
if (match(Op0, m_FMul(m_Value(OtherMul0), m_Value(OtherMul1)))) {
// Pattern: sqrt((x * y) * z)
if (OtherMul0 == OtherMul1) {
@@ -1435,8 +1437,6 @@
// Fast math flags for any created instructions should match the sqrt
// and multiply.
- // FIXME: We're not checking the sqrt because it doesn't have
- // fast-math-flags (see earlier comment).
IRBuilder<>::FastMathFlagGuard Guard(B);
B.SetFastMathFlags(I->getFastMathFlags());
// If we found a repeated factor, hoist it out of the square root and