[llvm] [InlineCost] Consider the default branch when calculating cost (PR #77856)

[Matt Arsenault via llvm-commits]

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@@ -446,6 +446,8 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
     /// inline cost heuristic, but it's a generic cost model to be used in other
     /// places (e.g., in loop unrolling).
     unsigned N = SI.getNumCases();
+    bool HasDefault =
+        !isa<UnreachableInst>(SI.getDefaultDest()->getFirstNonPHIOrDbg());
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arsenm wrote:

Can you move this default-is-unreachable into a helper on SwitchInst instead of repeating it twice?

https://github.com/llvm/llvm-project/pull/77856