1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
| //===- Reg2Mem.cpp - Convert registers to allocas -------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file demotes all registers to memory references. It is intended to be
// the inverse of PromoteMemoryToRegister. By converting to loads, the only
// values live across 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/ADT/Statistic.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils.h"
#include <list>
using namespace llvm;
#define DEBUG_TYPE "reg2mem"
STATISTIC(NumRegsDemoted, "Number of registers demoted");
STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted");
namespace {
struct RegToMem : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
RegToMem() : FunctionPass(ID) {
initializeRegToMemPass(*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequiredID(BreakCriticalEdgesID);
AU.addPreservedID(BreakCriticalEdgesID);
}
bool valueEscapes(const Instruction *Inst) const {
const BasicBlock *BB = Inst->getParent();
for (const User *U : Inst->users()) {
const Instruction *UI = cast<Instruction>(U);
if (UI->getParent() != BB || isa<PHINode>(UI))
return true;
}
return false;
}
bool runOnFunction(Function &F) override;
};
}
char RegToMem::ID = 0;
INITIALIZE_PASS_BEGIN(RegToMem, "reg2mem", "Demote all values to stack slots",
false, false)
INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
INITIALIZE_PASS_END(RegToMem, "reg2mem", "Demote all values to stack slots",
false, false)
bool RegToMem::runOnFunction(Function &F) {
if (F.isDeclaration() || skipFunction(F))
return false;
// Insert all new allocas into entry block.
BasicBlock *BBEntry = &F.getEntryBlock();
assert(pred_empty(BBEntry) &&
"Entry block to function must not have predecessors!");
// Find first non-alloca instruction and create insertion point. This is
// safe if block is well-formed: it always have terminator, otherwise
// we'll get and assertion.
BasicBlock::iterator I = BBEntry->begin();
while (isa<AllocaInst>(I)) ++I;
CastInst *AllocaInsertionPoint = new BitCastInst(
Constant::getNullValue(Type::getInt32Ty(F.getContext())),
Type::getInt32Ty(F.getContext()), "reg2mem alloca point", &*I);
// Find the escaped instructions. But don't create stack slots for
// allocas in entry block.
std::list<Instruction*> WorkList;
for (BasicBlock &ibb : F)
for (BasicBlock::iterator iib = ibb.begin(), iie = ibb.end(); iib != iie;
++iib) {
if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
valueEscapes(&*iib)) {
WorkList.push_front(&*iib);
}
}
// Demote escaped instructions
NumRegsDemoted += WorkList.size();
for (Instruction *ilb : WorkList)
DemoteRegToStack(*ilb, false, AllocaInsertionPoint);
WorkList.clear();
// Find all phi's
for (BasicBlock &ibb : F)
for (BasicBlock::iterator iib = ibb.begin(), iie = ibb.end(); iib != iie;
++iib)
if (isa<PHINode>(iib))
WorkList.push_front(&*iib);
// Demote phi nodes
NumPhisDemoted += WorkList.size();
for (Instruction *ilb : WorkList)
DemotePHIToStack(cast<PHINode>(ilb), AllocaInsertionPoint);
return true;
}
// createDemoteRegisterToMemory - Provide an entry point to create this pass.
char &llvm::DemoteRegisterToMemoryID = RegToMem::ID;
FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
return new RegToMem();
}
|