[llvm] [GlobalISel] Introduce `G_POISON` (PR #127825)

[Matt Arsenault via llvm-commits]

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@@ -11,3 +11,14 @@ define <4 x i1> @foo() {
 entry:
   ret <4 x i1> undef ;
 }
+
+define <4 x i1> @foo_poison() {
+  ; CHECK-LABEL: name: foo_poison
+  ; CHECK: bb.1.entry:
+  ; CHECK:   [[DEF:%[0-9]+]]:_(<4 x s1>) = G_POISON
+  ; CHECK:   [[ANYEXT:%[0-9]+]]:_(<4 x s32>) = G_ANYEXT [[DEF]](<4 x s1>)
+  ; CHECK:   $xmm0 = COPY [[ANYEXT]](<4 x s32>)
+  ; CHECK:   RET 0, implicit $xmm0
+entry:
+  ret <4 x i1> poison ;
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arsenm wrote:

don't need comment ; 

https://github.com/llvm/llvm-project/pull/127825