[llvm] [DirectX] Undo SimplifyCFG by reversing select into if else basic blocks (PR #153858)

[Farzon Lotfi via llvm-commits]

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@@ -622,6 +625,92 @@ legalizeScalarLoadStoreOnArrays(Instruction &I,
   return true;
 }
 
+// Note: Legalization to undo SimplifyCFG. Ideally, SimplifyCFG's
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farzonl wrote:

TODO: fix comment grammar, make shorter.

https://github.com/llvm/llvm-project/pull/153858