[llvm] [CodeGen][NPM] Update BranchFolderLegacy make tail merge configurable via flag (PR #135277)

[Matt Arsenault via llvm-commits]

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@@ -152,7 +162,8 @@ bool BranchFolderLegacy::runOnMachineFunction(MachineFunction &MF) {
   // TailMerge can create jump into if branches that make CFG irreducible for
   // HW that requires structurized CFG.
   bool EnableTailMerge = !MF.getTarget().requiresStructuredCFG() &&
-                         PassConfig->getEnableTailMerge();
+                         PassConfig->getEnableTailMerge() &&
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arsenm wrote:

What test hit the property error? I think SPIRV needs to cear NoPHIs property after its selection. It's bypassing the usual place it's cleared (though I'm not sure why it's cleared here)

https://github.com/llvm/llvm-project/pull/135277