[InstCombine] Preserve FMF for powi simplifications.

Differential Revision: https://reviews.llvm.org/D95455

Author: Valery N Dmitriev

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -886,15 +886,14 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
   case Intrinsic::powi:
     if (ConstantInt *Power = dyn_cast<ConstantInt>(II->getArgOperand(1))) {
       // 0 and 1 are handled in instsimplify
-
       // powi(x, -1) -> 1/x
       if (Power->isMinusOne())
-        return BinaryOperator::CreateFDiv(ConstantFP::get(CI.getType(), 1.0),
-                                          II->getArgOperand(0));
+        return BinaryOperator::CreateFDivFMF(ConstantFP::get(CI.getType(), 1.0),
+                                             II->getArgOperand(0), II);
       // powi(x, 2) -> x*x
       if (Power->equalsInt(2))
-        return BinaryOperator::CreateFMul(II->getArgOperand(0),
-                                          II->getArgOperand(0));
+        return BinaryOperator::CreateFMulFMF(II->getArgOperand(0),
+                                             II->getArgOperand(0), II);
     }
     break;
 

llvm/test/Transforms/InstCombine/intrinsics.ll

@@ -22,9 +22,9 @@ declare double @llvm.nearbyint.f64(double %Val) nounwind readonly
 
 define void @powi(double %V, double *%P) {
 ; CHECK-LABEL: @powi(
-; CHECK-NEXT:    [[A:%.*]] = fdiv double 1.000000e+00, [[V:%.*]]
+; CHECK-NEXT:    [[A:%.*]] = fdiv fast double 1.000000e+00, [[V:%.*]]
 ; CHECK-NEXT:    store volatile double [[A]], double* [[P:%.*]], align 8
-; CHECK-NEXT:    [[D:%.*]] = fmul double [[V]], [[V]]
+; CHECK-NEXT:    [[D:%.*]] = fmul nnan double [[V]], [[V]]
 ; CHECK-NEXT:    store volatile double [[D]], double* [[P]], align 8
 ; CHECK-NEXT:    ret void
 ;