AMDGPU: Make ballot intrinsic propagate poison

Author: arsenm

llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp

@@ -1049,7 +1049,11 @@ GCNTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
     break;
   }
   case Intrinsic::amdgcn_ballot: {
-    if (auto *Src = dyn_cast<ConstantInt>(II.getArgOperand(0))) {
+    Value *Arg = II.getArgOperand(0);
+    if (isa<PoisonValue>(Arg))
+      return IC.replaceInstUsesWith(II, PoisonValue::get(II.getType()));
+
+    if (auto *Src = dyn_cast<ConstantInt>(Arg)) {
       if (Src->isZero()) {
         // amdgcn.ballot(i1 0) is zero.
         return IC.replaceInstUsesWith(II, Constant::getNullValue(II.getType()));

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

@@ -2952,6 +2952,22 @@ define i32 @ballot_one_32() {
   ret i32 %b
 }
 
+define i64 @ballot_poison_64() {
+; CHECK-LABEL: @ballot_poison_64(
+; CHECK-NEXT:    ret i64 poison
+;
+  %b = call i64 @llvm.amdgcn.ballot.i64(i1 poison)
+  ret i64 %b
+}
+
+define i32 @ballot_poison_32() {
+; CHECK-LABEL: @ballot_poison_32(
+; CHECK-NEXT:    ret i32 poison
+;
+  %b = call i32 @llvm.amdgcn.ballot.i32(i1 poison)
+  ret i32 %b
+}
+
 ; --------------------------------------------------------------------
 ; llvm.amdgcn.wqm.vote
 ; --------------------------------------------------------------------