[NewPM] Remove Reg2Mem Legacy Pass (#73404)

This pass isn't used anywhere upstream and thus has no test coverage.
For these reasons it should be removed.

llvm/include/llvm/InitializePasses.h

@@ -260,7 +260,6 @@ void initializeRegAllocFastPass(PassRegistry&);
 void initializeRegAllocPriorityAdvisorAnalysisPass(PassRegistry &);
 void initializeRegAllocScoringPass(PassRegistry &);
 void initializeRegBankSelectPass(PassRegistry&);
-void initializeRegToMemLegacyPass(PassRegistry&);
 void initializeRegUsageInfoCollectorPass(PassRegistry&);
 void initializeRegUsageInfoPropagationPass(PassRegistry&);
 void initializeRegionInfoPassPass(PassRegistry&);

llvm/include/llvm/LinkAllPasses.h

@@ -97,7 +97,6 @@ namespace {
       (void) llvm::createNaryReassociatePass();
       (void) llvm::createObjCARCContractPass();
       (void) llvm::createPromoteMemoryToRegisterPass();
-      (void) llvm::createDemoteRegisterToMemoryPass();
       (void)llvm::createPostDomOnlyPrinterWrapperPassPass();
       (void)llvm::createPostDomPrinterWrapperPassPass();
       (void)llvm::createPostDomOnlyViewerWrapperPassPass();

llvm/include/llvm/Transforms/Scalar.h

@@ -74,15 +74,6 @@ Pass *createLoopUnrollPass(int OptLevel = 2, bool OnlyWhenForced = false,
 //
 Pass *createLoopRotatePass(int MaxHeaderSize = -1, bool PrepareForLTO = false);
 
-//===----------------------------------------------------------------------===//
-//
-// DemoteRegisterToMemoryPass - This pass is used to demote registers to memory
-// references. In basically undoes the PromoteMemoryToRegister pass to make cfg
-// hacking easier.
-//
-FunctionPass *createDemoteRegisterToMemoryPass();
-extern char &DemoteRegisterToMemoryID;
-
 //===----------------------------------------------------------------------===//
 //
 // Reassociate - This pass reassociates commutative expressions in an order that

llvm/lib/Transforms/Scalar/Reg2Mem.cpp

@@ -25,8 +25,6 @@
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/PassManager.h"
-#include "llvm/InitializePasses.h"
-#include "llvm/Pass.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
@@ -107,36 +105,3 @@ PreservedAnalyses RegToMemPass::run(Function &F, FunctionAnalysisManager &AM) {
   PA.preserve<LoopAnalysis>();
   return PA;
 }
-
-namespace {
-struct RegToMemLegacy : public FunctionPass {
-  static char ID; // Pass identification, replacement for typeid
-  RegToMemLegacy() : FunctionPass(ID) {
-    initializeRegToMemLegacyPass(*PassRegistry::getPassRegistry());
-  }
-
-  void getAnalysisUsage(AnalysisUsage &AU) const override {
-    AU.addRequiredID(BreakCriticalEdgesID);
-    AU.addPreservedID(BreakCriticalEdgesID);
-  }
-
-  bool runOnFunction(Function &F) override {
-    if (F.isDeclaration() || skipFunction(F))
-      return false;
-    return runPass(F);
-  }
-};
-} // namespace
-
-char RegToMemLegacy::ID = 0;
-INITIALIZE_PASS_BEGIN(RegToMemLegacy, "reg2mem",
-                      "Demote all values to stack slots", false, false)
-INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
-INITIALIZE_PASS_END(RegToMemLegacy, "reg2mem",
-                    "Demote all values to stack slots", false, false)
-
-// createDemoteRegisterToMemory - Provide an entry point to create this pass.
-char &llvm::DemoteRegisterToMemoryID = RegToMemLegacy::ID;
-FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
-  return new RegToMemLegacy();
-}

llvm/lib/Transforms/Scalar/Scalar.cpp

@@ -39,7 +39,6 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializePartiallyInlineLibCallsLegacyPassPass(Registry);
   initializeReassociateLegacyPassPass(Registry);
   initializeRedundantDbgInstEliminationPass(Registry);
-  initializeRegToMemLegacyPass(Registry);
   initializeScalarizeMaskedMemIntrinLegacyPassPass(Registry);
   initializeSROALegacyPassPass(Registry);
   initializeCFGSimplifyPassPass(Registry);