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/Compiler.h"
30 #include "llvm/Support/CFG.h"
34 STATISTIC(NumRegsDemoted, "Number of registers demoted");
35 STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted");
38 struct VISIBILITY_HIDDEN RegToMem : public FunctionPass {
39 static char ID; // Pass identification, replacement for typeid
40 RegToMem() : FunctionPass(&ID) {}
42 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
43 AU.addRequiredID(BreakCriticalEdgesID);
44 AU.addPreservedID(BreakCriticalEdgesID);
47 bool valueEscapes(Instruction* i) {
48 BasicBlock* bb = i->getParent();
49 for (Value::use_iterator ii = i->use_begin(), ie = i->use_end();
51 if (cast<Instruction>(*ii)->getParent() != bb ||
57 virtual bool runOnFunction(Function &F) {
58 if (!F.isDeclaration()) {
59 // Insert all new allocas into entry block.
60 BasicBlock* BBEntry = &F.getEntryBlock();
61 assert(pred_begin(BBEntry) == pred_end(BBEntry) &&
62 "Entry block to function must not have predecessors!");
64 // Find first non-alloca instruction and create insertion point. This is
65 // safe if block is well-formed: it always have terminator, otherwise
66 // we'll get and assertion.
67 BasicBlock::iterator I = BBEntry->begin();
68 while (isa<AllocaInst>(I)) ++I;
70 CastInst *AllocaInsertionPoint =
71 CastInst::Create(Instruction::BitCast,
72 F.getContext().getNullValue(Type::Int32Ty), Type::Int32Ty,
73 "reg2mem alloca point", I);
75 // Find the escaped instructions. But don't create stack slots for
76 // allocas in entry block.
77 std::list<Instruction*> worklist;
78 for (Function::iterator ibb = F.begin(), ibe = F.end();
80 for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
82 if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
84 worklist.push_front(&*iib);
88 // Demote escaped instructions
89 NumRegsDemoted += worklist.size();
90 for (std::list<Instruction*>::iterator ilb = worklist.begin(),
91 ile = worklist.end(); ilb != ile; ++ilb)
92 DemoteRegToStack(**ilb, false, AllocaInsertionPoint);
97 for (Function::iterator ibb = F.begin(), ibe = F.end();
99 for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
101 if (isa<PHINode>(iib))
102 worklist.push_front(&*iib);
105 NumPhisDemoted += worklist.size();
106 for (std::list<Instruction*>::iterator ilb = worklist.begin(),
107 ile = worklist.end(); ilb != ile; ++ilb)
108 DemotePHIToStack(cast<PHINode>(*ilb), AllocaInsertionPoint);
117 char RegToMem::ID = 0;
118 static RegisterPass<RegToMem>
119 X("reg2mem", "Demote all values to stack slots");
121 // createDemoteRegisterToMemory - Provide an entry point to create this pass.
123 const PassInfo *const llvm::DemoteRegisterToMemoryID = &X;
124 FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
125 return new RegToMem();