LowerExpectIntrinsic.cpp revision 234353 
1//===- LowerExpectIntrinsic.cpp - Lower expect intrinsic ------------------===//
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 pass lowers the 'expect' intrinsic to LLVM metadata.
11//
12//===----------------------------------------------------------------------===//
13
14#define DEBUG_TYPE "lower-expect-intrinsic"
15#include "llvm/Constants.h"
16#include "llvm/Function.h"
17#include "llvm/BasicBlock.h"
18#include "llvm/LLVMContext.h"
19#include "llvm/Instructions.h"
20#include "llvm/Intrinsics.h"
21#include "llvm/Metadata.h"
22#include "llvm/Pass.h"
23#include "llvm/Transforms/Scalar.h"
24#include "llvm/Support/CommandLine.h"
25#include "llvm/Support/Debug.h"
26#include "llvm/ADT/Statistic.h"
27#include <vector>
28
29using namespace llvm;
30
31STATISTIC(IfHandled, "Number of 'expect' intrinsic intructions handled");
32
33static cl::opt<uint32_t>
34LikelyBranchWeight("likely-branch-weight", cl::Hidden, cl::init(64),
35                   cl::desc("Weight of the branch likely to be taken (default = 64)"));
36static cl::opt<uint32_t>
37UnlikelyBranchWeight("unlikely-branch-weight", cl::Hidden, cl::init(4),
38                   cl::desc("Weight of the branch unlikely to be taken (default = 4)"));
39
40namespace {
41
42  class LowerExpectIntrinsic : public FunctionPass {
43
44    bool HandleSwitchExpect(SwitchInst *SI);
45
46    bool HandleIfExpect(BranchInst *BI);
47
48  public:
49    static char ID;
50    LowerExpectIntrinsic() : FunctionPass(ID) {
51      initializeLowerExpectIntrinsicPass(*PassRegistry::getPassRegistry());
52    }
53
54    bool runOnFunction(Function &F);
55  };
56}
57
58
59bool LowerExpectIntrinsic::HandleSwitchExpect(SwitchInst *SI) {
60  CallInst *CI = dyn_cast<CallInst>(SI->getCondition());
61  if (!CI)
62    return false;
63
64  Function *Fn = CI->getCalledFunction();
65  if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect)
66    return false;
67
68  Value *ArgValue = CI->getArgOperand(0);
69  ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1));
70  if (!ExpectedValue)
71    return false;
72
73  LLVMContext &Context = CI->getContext();
74  Type *Int32Ty = Type::getInt32Ty(Context);
75
76  SwitchInst::CaseIt Case = SI->findCaseValue(ExpectedValue);
77  std::vector<Value *> Vec;
78  unsigned n = SI->getNumCases();
79  Vec.resize(n + 1 + 1); // +1 for MDString and +1 for default case
80
81  Vec[0] = MDString::get(Context, "branch_weights");
82  Vec[1] = ConstantInt::get(Int32Ty, Case == SI->case_default() ?
83                            LikelyBranchWeight : UnlikelyBranchWeight);
84  for (unsigned i = 0; i < n; ++i) {
85    Vec[i + 1 + 1] = ConstantInt::get(Int32Ty, i == Case.getCaseIndex() ?
86        LikelyBranchWeight : UnlikelyBranchWeight);
87  }
88
89  MDNode *WeightsNode = llvm::MDNode::get(Context, Vec);
90  SI->setMetadata(LLVMContext::MD_prof, WeightsNode);
91
92  SI->setCondition(ArgValue);
93  return true;
94}
95
96
97bool LowerExpectIntrinsic::HandleIfExpect(BranchInst *BI) {
98  if (BI->isUnconditional())
99    return false;
100
101  // Handle non-optimized IR code like:
102  //   %expval = call i64 @llvm.expect.i64.i64(i64 %conv1, i64 1)
103  //   %tobool = icmp ne i64 %expval, 0
104  //   br i1 %tobool, label %if.then, label %if.end
105
106  ICmpInst *CmpI = dyn_cast<ICmpInst>(BI->getCondition());
107  if (!CmpI || CmpI->getPredicate() != CmpInst::ICMP_NE)
108    return false;
109
110  CallInst *CI = dyn_cast<CallInst>(CmpI->getOperand(0));
111  if (!CI)
112    return false;
113
114  Function *Fn = CI->getCalledFunction();
115  if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect)
116    return false;
117
118  Value *ArgValue = CI->getArgOperand(0);
119  ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1));
120  if (!ExpectedValue)
121    return false;
122
123  LLVMContext &Context = CI->getContext();
124  Type *Int32Ty = Type::getInt32Ty(Context);
125  bool Likely = ExpectedValue->isOne();
126
127  // If expect value is equal to 1 it means that we are more likely to take
128  // branch 0, in other case more likely is branch 1.
129  Value *Ops[] = {
130    MDString::get(Context, "branch_weights"),
131    ConstantInt::get(Int32Ty, Likely ? LikelyBranchWeight : UnlikelyBranchWeight),
132    ConstantInt::get(Int32Ty, Likely ? UnlikelyBranchWeight : LikelyBranchWeight)
133  };
134
135  MDNode *WeightsNode = MDNode::get(Context, Ops);
136  BI->setMetadata(LLVMContext::MD_prof, WeightsNode);
137
138  CmpI->setOperand(0, ArgValue);
139  return true;
140}
141
142
143bool LowerExpectIntrinsic::runOnFunction(Function &F) {
144  for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
145    BasicBlock *BB = I++;
146
147    // Create "block_weights" metadata.
148    if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
149      if (HandleIfExpect(BI))
150        IfHandled++;
151    } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
152      if (HandleSwitchExpect(SI))
153        IfHandled++;
154    }
155
156    // remove llvm.expect intrinsics.
157    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
158         BI != BE; ) {
159      CallInst *CI = dyn_cast<CallInst>(BI++);
160      if (!CI)
161        continue;
162
163      Function *Fn = CI->getCalledFunction();
164      if (Fn && Fn->getIntrinsicID() == Intrinsic::expect) {
165        Value *Exp = CI->getArgOperand(0);
166        CI->replaceAllUsesWith(Exp);
167        CI->eraseFromParent();
168      }
169    }
170  }
171
172  return false;
173}
174
175
176char LowerExpectIntrinsic::ID = 0;
177INITIALIZE_PASS(LowerExpectIntrinsic, "lower-expect", "Lower 'expect' "
178                "Intrinsics", false, false)
179
180FunctionPass *llvm::createLowerExpectIntrinsicPass() {
181  return new LowerExpectIntrinsic();
182}
183