1 //===- Reg2Mem.cpp - Convert registers to allocas -------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file demotes all registers to memory references. It is intented to be
11 // the inverse of PromoteMemoryToRegister. By converting to loads, the only
12 // values live accross basic blocks are allocas and loads before phi nodes.
13 // It is intended that this should make CFG hacking much easier.
14 // To make later hacking easier, the entry block is split into two, such that
15 // all introduced allocas and nothing else are in the entry block.
17 //===----------------------------------------------------------------------===//
19 #define DEBUG_TYPE "reg2mem"
20 #include "llvm/Transforms/Scalar.h"
21 #include "llvm/Transforms/Utils/Local.h"
22 #include "llvm/Pass.h"
23 #include "llvm/Function.h"
24 #include "llvm/LLVMContext.h"
25 #include "llvm/Module.h"
26 #include "llvm/BasicBlock.h"
27 #include "llvm/Instructions.h"
28 #include "llvm/ADT/Statistic.h"
29 #include "llvm/Support/CFG.h"
33 STATISTIC(NumRegsDemoted, "Number of registers demoted");
34 STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted");
37 struct RegToMem : public FunctionPass {
38 static char ID; // Pass identification, replacement for typeid
39 RegToMem() : FunctionPass(&ID) {}
41 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
42 AU.addRequiredID(BreakCriticalEdgesID);
43 AU.addPreservedID(BreakCriticalEdgesID);
46 bool valueEscapes(const Instruction *Inst) const {
47 const BasicBlock *BB = Inst->getParent();
48 for (Value::use_const_iterator UI = Inst->use_begin(),E = Inst->use_end();
50 if (cast<Instruction>(*UI)->getParent() != BB ||
56 virtual bool runOnFunction(Function &F);
60 char RegToMem::ID = 0;
61 static RegisterPass<RegToMem>
62 X("reg2mem", "Demote all values to stack slots");
65 bool RegToMem::runOnFunction(Function &F) {
66 if (F.isDeclaration())
69 // Insert all new allocas into entry block.
70 BasicBlock *BBEntry = &F.getEntryBlock();
71 assert(pred_begin(BBEntry) == pred_end(BBEntry) &&
72 "Entry block to function must not have predecessors!");
74 // Find first non-alloca instruction and create insertion point. This is
75 // safe if block is well-formed: it always have terminator, otherwise
76 // we'll get and assertion.
77 BasicBlock::iterator I = BBEntry->begin();
78 while (isa<AllocaInst>(I)) ++I;
80 CastInst *AllocaInsertionPoint =
81 new BitCastInst(Constant::getNullValue(Type::getInt32Ty(F.getContext())),
82 Type::getInt32Ty(F.getContext()),
83 "reg2mem alloca point", I);
85 // Find the escaped instructions. But don't create stack slots for
86 // allocas in entry block.
87 std::list<Instruction*> WorkList;
88 for (Function::iterator ibb = F.begin(), ibe = F.end();
90 for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
92 if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
94 WorkList.push_front(&*iib);
98 // Demote escaped instructions
99 NumRegsDemoted += WorkList.size();
100 for (std::list<Instruction*>::iterator ilb = WorkList.begin(),
101 ile = WorkList.end(); ilb != ile; ++ilb)
102 DemoteRegToStack(**ilb, false, AllocaInsertionPoint);
107 for (Function::iterator ibb = F.begin(), ibe = F.end();
109 for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
111 if (isa<PHINode>(iib))
112 WorkList.push_front(&*iib);
115 NumPhisDemoted += WorkList.size();
116 for (std::list<Instruction*>::iterator ilb = WorkList.begin(),
117 ile = WorkList.end(); ilb != ile; ++ilb)
118 DemotePHIToStack(cast<PHINode>(*ilb), AllocaInsertionPoint);
124 // createDemoteRegisterToMemory - Provide an entry point to create this pass.
126 const PassInfo *const llvm::DemoteRegisterToMemoryID = &X;
127 FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
128 return new RegToMem();