1 //===- Reg2Mem.cpp - Convert registers to allocas -------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file demotes all registers to memory references. It is intended to be
11 // the inverse of PromoteMemoryToRegister. By converting to loads, the only
12 // values live across 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.
16 //
17 //===----------------------------------------------------------------------===//
18
19 #include "llvm/Transforms/Scalar.h"
20 #include "llvm/ADT/Statistic.h"
21 #include "llvm/IR/BasicBlock.h"
22 #include "llvm/IR/CFG.h"
23 #include "llvm/IR/Function.h"
24 #include "llvm/IR/Instructions.h"
25 #include "llvm/IR/LLVMContext.h"
26 #include "llvm/IR/Module.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Transforms/Utils/Local.h"
29 #include <list>
30 using namespace llvm;
31
32 #define DEBUG_TYPE "reg2mem"
33
34 STATISTIC(NumRegsDemoted, "Number of registers demoted");
35 STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted");
36
37 namespace {
38 struct RegToMem : public FunctionPass {
39 static char ID; // Pass identification, replacement for typeid
RegToMem__anon6ea3a00d0111::RegToMem40 RegToMem() : FunctionPass(ID) {
41 initializeRegToMemPass(*PassRegistry::getPassRegistry());
42 }
43
getAnalysisUsage__anon6ea3a00d0111::RegToMem44 void getAnalysisUsage(AnalysisUsage &AU) const override {
45 AU.addRequiredID(BreakCriticalEdgesID);
46 AU.addPreservedID(BreakCriticalEdgesID);
47 }
48
valueEscapes__anon6ea3a00d0111::RegToMem49 bool valueEscapes(const Instruction *Inst) const {
50 const BasicBlock *BB = Inst->getParent();
51 for (const User *U : Inst->users()) {
52 const Instruction *UI = cast<Instruction>(U);
53 if (UI->getParent() != BB || isa<PHINode>(UI))
54 return true;
55 }
56 return false;
57 }
58
59 bool runOnFunction(Function &F) override;
60 };
61 }
62
63 char RegToMem::ID = 0;
64 INITIALIZE_PASS_BEGIN(RegToMem, "reg2mem", "Demote all values to stack slots",
65 false, false)
INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)66 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
67 INITIALIZE_PASS_END(RegToMem, "reg2mem", "Demote all values to stack slots",
68 false, false)
69
70 bool RegToMem::runOnFunction(Function &F) {
71 if (F.isDeclaration() || skipFunction(F))
72 return false;
73
74 // Insert all new allocas into entry block.
75 BasicBlock *BBEntry = &F.getEntryBlock();
76 assert(pred_empty(BBEntry) &&
77 "Entry block to function must not have predecessors!");
78
79 // Find first non-alloca instruction and create insertion point. This is
80 // safe if block is well-formed: it always have terminator, otherwise
81 // we'll get and assertion.
82 BasicBlock::iterator I = BBEntry->begin();
83 while (isa<AllocaInst>(I)) ++I;
84
85 CastInst *AllocaInsertionPoint = new BitCastInst(
86 Constant::getNullValue(Type::getInt32Ty(F.getContext())),
87 Type::getInt32Ty(F.getContext()), "reg2mem alloca point", &*I);
88
89 // Find the escaped instructions. But don't create stack slots for
90 // allocas in entry block.
91 std::list<Instruction*> WorkList;
92 for (BasicBlock &ibb : F)
93 for (BasicBlock::iterator iib = ibb.begin(), iie = ibb.end(); iib != iie;
94 ++iib) {
95 if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
96 valueEscapes(&*iib)) {
97 WorkList.push_front(&*iib);
98 }
99 }
100
101 // Demote escaped instructions
102 NumRegsDemoted += WorkList.size();
103 for (Instruction *ilb : WorkList)
104 DemoteRegToStack(*ilb, false, AllocaInsertionPoint);
105
106 WorkList.clear();
107
108 // Find all phi's
109 for (BasicBlock &ibb : F)
110 for (BasicBlock::iterator iib = ibb.begin(), iie = ibb.end(); iib != iie;
111 ++iib)
112 if (isa<PHINode>(iib))
113 WorkList.push_front(&*iib);
114
115 // Demote phi nodes
116 NumPhisDemoted += WorkList.size();
117 for (Instruction *ilb : WorkList)
118 DemotePHIToStack(cast<PHINode>(ilb), AllocaInsertionPoint);
119
120 return true;
121 }
122
123
124 // createDemoteRegisterToMemory - Provide an entry point to create this pass.
125 char &llvm::DemoteRegisterToMemoryID = RegToMem::ID;
createDemoteRegisterToMemoryPass()126 FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
127 return new RegToMem();
128 }
129