[Reg2Mem] Add legacy pass wrapping Reg2Mem (#111024)

The SPIR-V backend will need to use Reg2Mem, hence this pass needs to be
wrapped to be used with the legacy pass manager.

---------

Signed-off-by: Nathan Gauër <[email protected]>

Author: Keenuts

llvm/include/llvm/InitializePasses.h

@@ -256,6 +256,7 @@ void initializeRegAllocFastPass(PassRegistry &);
 void initializeRegAllocPriorityAdvisorAnalysisPass(PassRegistry &);
 void initializeRegAllocScoringPass(PassRegistry &);
 void initializeRegBankSelectPass(PassRegistry &);
+void initializeRegToMemWrapperPassPass(PassRegistry &);
 void initializeRegUsageInfoCollectorPass(PassRegistry &);
 void initializeRegUsageInfoPropagationPass(PassRegistry &);
 void initializeRegionInfoPassPass(PassRegistry &);

llvm/include/llvm/LinkAllPasses.h

@@ -98,6 +98,7 @@ struct ForcePassLinking {
     (void)llvm::createNaryReassociatePass();
     (void)llvm::createObjCARCContractPass();
     (void)llvm::createPromoteMemoryToRegisterPass();
+    (void)llvm::createRegToMemWrapperPass();
     (void)llvm::createPostDomOnlyPrinterWrapperPassPass();
     (void)llvm::createPostDomPrinterWrapperPassPass();
     (void)llvm::createPostDomOnlyViewerWrapperPassPass();

llvm/include/llvm/Transforms/Utils.h

@@ -81,6 +81,14 @@ extern char &LCSSAID;
 //
 FunctionPass *createPromoteMemoryToRegisterPass();
 
+//===----------------------------------------------------------------------===//
+//
+// RegToMemWrapperPass - This pass is used to demote registers to memory
+// references. In basically undoes the PromoteMemoryToRegister pass to make cfg
+// hacking easier.
+//
+FunctionPass *createRegToMemWrapperPass();
+
 //===----------------------------------------------------------------------===//
 //
 // LoopSimplify - Insert Pre-header blocks into the CFG for every function in

llvm/lib/Transforms/Scalar/Reg2Mem.cpp

@@ -25,6 +25,7 @@
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/PassManager.h"
+#include "llvm/InitializePasses.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
@@ -105,3 +106,45 @@ PreservedAnalyses RegToMemPass::run(Function &F, FunctionAnalysisManager &AM) {
   PA.preserve<LoopAnalysis>();
   return PA;
 }
+
+namespace llvm {
+
+void initializeRegToMemWrapperPassPass(PassRegistry &);
+
+class RegToMemWrapperPass : public FunctionPass {
+public:
+  static char ID;
+
+  RegToMemWrapperPass() : FunctionPass(ID) {}
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesAll();
+
+    AU.addPreserved<DominatorTreeWrapperPass>();
+    AU.addRequired<DominatorTreeWrapperPass>();
+
+    AU.addPreserved<LoopInfoWrapperPass>();
+    AU.addRequired<LoopInfoWrapperPass>();
+  }
+
+  bool runOnFunction(Function &F) override {
+    DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+    LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+
+    unsigned N = SplitAllCriticalEdges(F, CriticalEdgeSplittingOptions(DT, LI));
+    bool Changed = runPass(F);
+    return N != 0 || Changed;
+  }
+};
+} // namespace llvm
+
+INITIALIZE_PASS_BEGIN(RegToMemWrapperPass, "reg2mem", "", true, true)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass);
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass);
+INITIALIZE_PASS_END(RegToMemWrapperPass, "reg2mem", "", true, true)
+
+char RegToMemWrapperPass::ID = 0;
+
+FunctionPass *llvm::createRegToMemWrapperPass() {
+  return new RegToMemWrapperPass();
+}