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

[Matt Arsenault via llvm-commits]

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@@ -707,6 +707,10 @@ void TargetPassConfig::addPass(Pass *P) {
   // and shouldn't reference it.
   AnalysisID PassID = P->getPassID();
 
+  IdentifyingPassPtr TargetID = getPassSubstitution(PassID);
+  if (!overridePass(PassID, TargetID).isValid())
+    return;
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arsenm wrote:

Shouldn't need to touch the override infrastructure? 

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