AMDGPU: Make rcp intrinsic propagate poison

Author: arsenm

llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp

@@ -487,6 +487,8 @@ GCNTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
   switch (IID) {
   case Intrinsic::amdgcn_rcp: {
     Value *Src = II.getArgOperand(0);
+    if (isa<PoisonValue>(Src))
+      return IC.replaceInstUsesWith(II, Src);
 
     // TODO: Move to ConstantFolding/InstSimplify?
     if (isa<UndefValue>(Src)) {

llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll

@@ -8,6 +8,14 @@
 declare float @llvm.amdgcn.rcp.f32(float) nounwind readnone
 declare double @llvm.amdgcn.rcp.f64(double) nounwind readnone
 
+define float @test_constant_fold_rcp_f32_poison() nounwind {
+; CHECK-LABEL: @test_constant_fold_rcp_f32_poison(
+; CHECK-NEXT:    ret float poison
+;
+  %val = call float @llvm.amdgcn.rcp.f32(float poison) nounwind readnone
+  ret float %val
+}
+
 define float @test_constant_fold_rcp_f32_undef() nounwind {
 ; CHECK-LABEL: @test_constant_fold_rcp_f32_undef(
 ; CHECK-NEXT:    ret float 0x7FF8000000000000