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::const_use_iterator UI = Inst->use_begin(),E = Inst->use_end();
50 const Instruction *I = cast<Instruction>(*UI);
51 if (I->getParent() != BB || isa<PHINode>(I))
57 virtual bool runOnFunction(Function &F);
61 char RegToMem::ID = 0;
62 INITIALIZE_PASS_BEGIN(RegToMem, "reg2mem", "Demote all values to stack slots",
64 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
65 INITIALIZE_PASS_END(RegToMem, "reg2mem", "Demote all values to stack slots",
68 bool RegToMem::runOnFunction(Function &F) {
69 if (F.isDeclaration())
72 // Insert all new allocas into entry block.
73 BasicBlock *BBEntry = &F.getEntryBlock();
74 assert(pred_begin(BBEntry) == pred_end(BBEntry) &&
75 "Entry block to function must not have predecessors!");
77 // Find first non-alloca instruction and create insertion point. This is
78 // safe if block is well-formed: it always have terminator, otherwise
79 // we'll get and assertion.
80 BasicBlock::iterator I = BBEntry->begin();
81 while (isa<AllocaInst>(I)) ++I;
83 CastInst *AllocaInsertionPoint =
84 new BitCastInst(Constant::getNullValue(Type::getInt32Ty(F.getContext())),
85 Type::getInt32Ty(F.getContext()),
86 "reg2mem alloca point", I);
88 // Find the escaped instructions. But don't create stack slots for
89 // allocas in entry block.
90 std::list<Instruction*> WorkList;
91 for (Function::iterator ibb = F.begin(), ibe = F.end();
93 for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
95 if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
97 WorkList.push_front(&*iib);
101 // Demote escaped instructions
102 NumRegsDemoted += WorkList.size();
103 for (std::list<Instruction*>::iterator ilb = WorkList.begin(),
104 ile = WorkList.end(); ilb != ile; ++ilb)
105 DemoteRegToStack(**ilb, false, AllocaInsertionPoint);
110 for (Function::iterator ibb = F.begin(), ibe = F.end();
112 for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
114 if (isa<PHINode>(iib))
115 WorkList.push_front(&*iib);
118 NumPhisDemoted += WorkList.size();
119 for (std::list<Instruction*>::iterator ilb = WorkList.begin(),
120 ile = WorkList.end(); ilb != ile; ++ilb)
121 DemotePHIToStack(cast<PHINode>(*ilb), AllocaInsertionPoint);
127 // createDemoteRegisterToMemory - Provide an entry point to create this pass.
129 char &llvm::DemoteRegisterToMemoryID = RegToMem::ID;
130 FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
131 return new RegToMem();