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

[Cullen Rhodes 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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c-rhodes wrote:

looks like there's already a test for this: https://github.com/llvm/llvm-project/blob/cc251197a0a12a289acf99c7ead7938d695b0905/llvm/unittests/Analysis/ValueTrackingTest.cpp#L1180-L1182

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