[NewPM] Remove UnifyFunctionExitNodesLegacyPass (#72816)

UnifyFunctionExitNodesLegacyPass isn't used anywhere in upstream and
thus isn't tested at all. For these reasons, remove it.

Author: boomanaiden154

llvm/include/llvm/InitializePasses.h

@@ -323,7 +323,6 @@ void initializeTwoAddressInstructionPassPass(PassRegistry&);
 void initializeTypeBasedAAWrapperPassPass(PassRegistry&);
 void initializeTypePromotionLegacyPass(PassRegistry&);
 void initializeUniformityInfoWrapperPassPass(PassRegistry &);
-void initializeUnifyFunctionExitNodesLegacyPassPass(PassRegistry &);
 void initializeUnifyLoopExitsLegacyPassPass(PassRegistry &);
 void initializeUnpackMachineBundlesPass(PassRegistry&);
 void initializeUnreachableBlockElimLegacyPassPass(PassRegistry&);

llvm/include/llvm/LinkAllPasses.h

@@ -44,7 +44,6 @@
 #include "llvm/Transforms/Scalar/Scalarizer.h"
 #include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Utils/SymbolRewriter.h"
-#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
 #include "llvm/Transforms/Vectorize/LoadStoreVectorizer.h"
 #include <cstdlib>
 
@@ -119,7 +118,6 @@ namespace {
       (void) llvm::createSingleLoopExtractorPass();
       (void) llvm::createTailCallEliminationPass();
       (void)llvm::createTLSVariableHoistPass();
-      (void) llvm::createUnifyFunctionExitNodesPass();
       (void) llvm::createInstCountPass();
       (void) llvm::createConstantHoistingPass();
       (void) llvm::createCodeGenPreparePass();

llvm/include/llvm/Transforms/Utils/UnifyFunctionExitNodes.h

@@ -19,19 +19,6 @@
 
 namespace llvm {
 
-class UnifyFunctionExitNodesLegacyPass : public FunctionPass {
-public:
-  static char ID; // Pass identification, replacement for typeid
-  UnifyFunctionExitNodesLegacyPass();
-
-  // We can preserve non-critical-edgeness when we unify function exit nodes
-  void getAnalysisUsage(AnalysisUsage &AU) const override;
-
-  bool runOnFunction(Function &F) override;
-};
-
-Pass *createUnifyFunctionExitNodesPass();
-
 class UnifyFunctionExitNodesPass
     : public PassInfoMixin<UnifyFunctionExitNodesPass> {
 public:

llvm/lib/Transforms/Utils/UnifyFunctionExitNodes.cpp

@@ -16,31 +16,9 @@
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Type.h"
-#include "llvm/InitializePasses.h"
 #include "llvm/Transforms/Utils.h"
 using namespace llvm;
 
-char UnifyFunctionExitNodesLegacyPass::ID = 0;
-
-UnifyFunctionExitNodesLegacyPass::UnifyFunctionExitNodesLegacyPass()
-    : FunctionPass(ID) {
-  initializeUnifyFunctionExitNodesLegacyPassPass(
-      *PassRegistry::getPassRegistry());
-}
-
-INITIALIZE_PASS(UnifyFunctionExitNodesLegacyPass, "mergereturn",
-                "Unify function exit nodes", false, false)
-
-Pass *llvm::createUnifyFunctionExitNodesPass() {
-  return new UnifyFunctionExitNodesLegacyPass();
-}
-
-void UnifyFunctionExitNodesLegacyPass::getAnalysisUsage(
-    AnalysisUsage &AU) const {
-  // We preserve the non-critical-edgeness property
-  AU.addPreservedID(BreakCriticalEdgesID);
-}
-
 namespace {
 
 bool unifyUnreachableBlocks(Function &F) {
@@ -108,16 +86,6 @@ bool unifyReturnBlocks(Function &F) {
 }
 } // namespace
 
-// Unify all exit nodes of the CFG by creating a new BasicBlock, and converting
-// all returns to unconditional branches to this new basic block. Also, unify
-// all unreachable blocks.
-bool UnifyFunctionExitNodesLegacyPass::runOnFunction(Function &F) {
-  bool Changed = false;
-  Changed |= unifyUnreachableBlocks(F);
-  Changed |= unifyReturnBlocks(F);
-  return Changed;
-}
-
 PreservedAnalyses UnifyFunctionExitNodesPass::run(Function &F,
                                                   FunctionAnalysisManager &AM) {
   bool Changed = false;

llvm/lib/Transforms/Utils/Utils.cpp

@@ -30,7 +30,6 @@ void llvm::initializeTransformUtils(PassRegistry &Registry) {
   initializeLowerInvokeLegacyPassPass(Registry);
   initializeLowerSwitchLegacyPassPass(Registry);
   initializePromoteLegacyPassPass(Registry);
-  initializeUnifyFunctionExitNodesLegacyPassPass(Registry);
   initializeStripGCRelocatesLegacyPass(Registry);
   initializePredicateInfoPrinterLegacyPassPass(Registry);
   initializeFixIrreduciblePass(Registry);