[llvm] [ValueTracking] Teach isGuaranteedNotToBeUndefOrPoison about splats (PR #163570)

[Nikita Popov via llvm-commits]

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@@ -7695,6 +7696,10 @@ static bool isGuaranteedNotToBeUndefOrPoison(
         }
         if (IsWellDefined)
           return true;
+      } else if (isa<ShuffleVectorInst>(Opr) && (Splat = getSplatValue(Opr))) {
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nikic wrote:

It would make sense to test this specifically for the splat case as well (in the IR test -- the unit test looks redundant to me).

https://github.com/llvm/llvm-project/pull/163570