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

[Antonio Frighetto 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))) {
+        // For splats we only need to check the value being splatted.
+        if (OpCheck(Splat))
+          return true;
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antoniofrighetto wrote:

Have one line for the splat value check?
```suggestion
      } else if (isa<ShuffleVectorInst>(Opr)) {
        // For splats we only need to check the value being splatted.
        if (auto *Splat = getSplatValue(Opr); Splat && OpCheck(Splat))
          return true;
```

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