[LibCallSimplifier] use instruction-level fast-math-flags to transform pow(x, 0.5) calls

Also, propagate the FMF to the newly created sqrt() call.

llvm-svn: 257503

2 files changed, 10 insertions, 9 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 2551abef75b..dc074406014 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1164,9 +1164,12 @@ Value *LibCallSimplifier::optimizePow(CallInst *CI, IRBuilder<> &B) {
                       LibFunc::fabsl)) {
 
     // In -ffast-math, pow(x, 0.5) -> sqrt(x).
-    if (UnsafeFPMath)
+    if (CI->hasUnsafeAlgebra()) {
+      IRBuilder<>::FastMathFlagGuard Guard(B);
+      B.setFastMathFlags(CI->getFastMathFlags());
       return EmitUnaryFloatFnCall(Op1, TLI->getName(LibFunc::sqrt), B,
                                   Callee->getAttributes());
+    }
 
     // Expand pow(x, 0.5) to (x == -infinity ? +infinity : fabs(sqrt(x))).
     // This is faster than calling pow, and still handles negative zero
diff --git a/llvm/test/Transforms/InstCombine/pow-sqrt.ll b/llvm/test/Transforms/InstCombine/pow-sqrt.ll
index 8fc74e4a002..1e6166c5f11 100644
--- a/llvm/test/Transforms/InstCombine/pow-sqrt.ll
+++ b/llvm/test/Transforms/InstCombine/pow-sqrt.ll
@@ -1,15 +1,13 @@
 ; RUN: opt < %s -instcombine -S | FileCheck %s
 
-define double @mypow(double %x) #0 {
-entry:
-  %pow = call double @llvm.pow.f64(double %x, double 5.000000e-01)
+define double @pow_half(double %x) {
+  %pow = call fast double @llvm.pow.f64(double %x, double 5.000000e-01)
   ret double %pow
 }
 
-; CHECK-LABEL: define double @mypow(
-; CHECK:   %sqrt = call double @sqrt(double %x) #1
-; CHECK:   ret double %sqrt
-; CHECK: }
+; CHECK-LABEL: define double @pow_half(
+; CHECK-NEXT:  %sqrt = call fast double @sqrt(double %x)
+; CHECK-NEXT:  ret double %sqrt
 
 declare double @llvm.pow.f64(double, double)
-attributes #0 = { "unsafe-fp-math"="true" }
+