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

[David Sherwood via cfe-commits]

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@@ -7695,6 +7695,11 @@ static bool isGuaranteedNotToBeUndefOrPoison(
         }
         if (IsWellDefined)
           return true;
+      } else if (auto *Splat = isa<ShuffleVectorInst>(Opr) ? getSplatValue(Opr)
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david-arm wrote:

Just curious about how `auto` actually works here when selecting between two possibilities? It could choose `nullptr`, in which case it might be `void *` I presume? I can only assume it creates the type based on the first option, i.e. `getSplatValue`. I just wasn't sure whether the code compiles because of luck or an actual C++ specification based on ordering.

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