The pass everyone has been waiting for!

Reg2Mem

for fun you can opt -reg2mem -mem2reg

llvm-svn: 24267

llvm/include/llvm/Transforms/Scalar.h

@@ -162,6 +162,12 @@ FunctionPass *createLoopUnrollPass();
 //
 FunctionPass *createPromoteMemoryToRegisterPass();
 
+//===----------------------------------------------------------------------===//
+//
+// This pass is used to demote registers to memory references .
+// In basically undoes the PromoteMemoryToRegister pass to
+// make cfg hacking easier.
+FunctionPass *createDemoteRegisterToMemoryPass();
 
 //===----------------------------------------------------------------------===//
 //

llvm/lib/Transforms/Scalar/Reg2Mem.cpp

@@ -0,0 +1,79 @@
+//===- Reg2Mem.cpp - Convert registers to allocas -------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file demotes all registers to memory references.  It is intented to be
+// the inverse of PromoteMemoryToRegister.  By converting to loads, the only
+// values live accross basic blocks are allocas and loads before phi nodes.
+// It is intended that this should make CFG hacking much easier.
+// To make later hacking easier, the entry block is split into two, such that
+// all introduced allocas and nothing else are in the entry block.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Pass.h"
+#include "llvm/Function.h"
+#include "llvm/Module.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/Instructions.h"
+#include "llvm/ADT/Statistic.h"
+
+#include <list>
+
+using namespace llvm;
+
+namespace {
+  Statistic<> NumDemoted("reg2mem", "Number of registers demoted");
+  
+  struct RegToMem : public FunctionPass {
+
+   bool valueEscapes(Instruction* i) {
+      BasicBlock* bb = i->getParent();
+      for(Value::use_iterator ii = i->use_begin(), ie = i->use_end();
+          ii != ie; ++ii)
+        if (cast<Instruction>(*ii)->getParent() != bb)
+          return true;
+      return false;
+    }
+
+    virtual bool runOnFunction(Function &F) {
+      if (!F.isExternal()) {
+        //give us a clean block
+        BasicBlock& bbhead = F.getEntryBlock();
+        bbhead.splitBasicBlock(bbhead.begin());
+
+        //find the instructions
+        std::list<Instruction*> worklist;
+        for (Function::iterator ibb = F.begin(), ibe = F.end();
+             ibb != ibe; ++ibb)
+          for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
+               iib != iie; ++iib) {
+            if(valueEscapes(iib))
+              worklist.push_front(&*iib);
+          }
+        //demote escaped instructions
+        NumDemoted += worklist.size();
+        for (std::list<Instruction*>::iterator ilb = worklist.begin(), 
+               ile = worklist.end(); ilb != ile; ++ilb)
+          DemoteRegToStack(**ilb, false);
+        return true;
+      }
+      return false;
+    }
+  };
+  
+  RegisterOpt<RegToMem> X("reg2mem", "Demote all values to stack slots");
+}
+
+// createDemoteRegisterToMemory - Provide an entry point to create this pass.
+//
+FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
+  return new RegToMem();
+}