[llvm] AMDGPU: Make cvt_pknorm and cvt_pk intrinsics propagate poison (PR #131059)

[Matt Arsenault via llvm-commits]

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@@ -1320,6 +1320,30 @@ define <2 x i16> @undef_cvt_pknorm_i16() {
   ret <2 x i16> %cvt
 }
 
+define <2 x i16> @poison_lhs_cvt_pknorm_i16(float %y) {
+; CHECK-LABEL: @poison_lhs_cvt_pknorm_i16(
+; CHECK-NEXT:    ret <2 x i16> poison
+;
+  %cvt = call <2 x i16> @llvm.amdgcn.cvt.pknorm.i16(float poison, float %y)
+  ret <2 x i16> %cvt
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arsenm wrote:

Maybe we should be only propagating poison for the one element. That's how the IR casts would behave 

https://github.com/llvm/llvm-project/pull/131059