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 #include "llvm/Transforms/Scalar.h"
15 #include "llvm/ADT/Statistic.h"
16 #include "llvm/IR/BasicBlock.h"
17 #include "llvm/IR/Constants.h"
18 #include "llvm/IR/Function.h"
19 #include "llvm/IR/Instructions.h"
20 #include "llvm/IR/Intrinsics.h"
21 #include "llvm/IR/LLVMContext.h"
22 #include "llvm/IR/MDBuilder.h"
23 #include "llvm/IR/Metadata.h"
24 #include "llvm/Pass.h"
25 #include "llvm/Support/CommandLine.h"
26 #include "llvm/Support/Debug.h"
27 #include <vector>
28
29 using namespace llvm;
30
31 #define DEBUG_TYPE "lower-expect-intrinsic"
32
33 STATISTIC(IfHandled, "Number of 'expect' intrinsic instructions handled");
34
35 static cl::opt<uint32_t>
36 LikelyBranchWeight("likely-branch-weight", cl::Hidden, cl::init(64),
37 cl::desc("Weight of the branch likely to be taken (default = 64)"));
38 static cl::opt<uint32_t>
39 UnlikelyBranchWeight("unlikely-branch-weight", cl::Hidden, cl::init(4),
40 cl::desc("Weight of the branch unlikely to be taken (default = 4)"));
41
42 namespace {
43
44 class LowerExpectIntrinsic : public FunctionPass {
45
46 bool HandleSwitchExpect(SwitchInst *SI);
47
48 bool HandleIfExpect(BranchInst *BI);
49
50 public:
51 static char ID;
LowerExpectIntrinsic()52 LowerExpectIntrinsic() : FunctionPass(ID) {
53 initializeLowerExpectIntrinsicPass(*PassRegistry::getPassRegistry());
54 }
55
56 bool runOnFunction(Function &F) override;
57 };
58 }
59
60
HandleSwitchExpect(SwitchInst * SI)61 bool LowerExpectIntrinsic::HandleSwitchExpect(SwitchInst *SI) {
62 CallInst *CI = dyn_cast<CallInst>(SI->getCondition());
63 if (!CI)
64 return false;
65
66 Function *Fn = CI->getCalledFunction();
67 if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect)
68 return false;
69
70 Value *ArgValue = CI->getArgOperand(0);
71 ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1));
72 if (!ExpectedValue)
73 return false;
74
75 SwitchInst::CaseIt Case = SI->findCaseValue(ExpectedValue);
76 unsigned n = SI->getNumCases(); // +1 for default case.
77 std::vector<uint32_t> Weights(n + 1);
78
79 Weights[0] = Case == SI->case_default() ? LikelyBranchWeight
80 : UnlikelyBranchWeight;
81 for (unsigned i = 0; i != n; ++i)
82 Weights[i + 1] = i == Case.getCaseIndex() ? LikelyBranchWeight
83 : UnlikelyBranchWeight;
84
85 SI->setMetadata(LLVMContext::MD_prof,
86 MDBuilder(CI->getContext()).createBranchWeights(Weights));
87
88 SI->setCondition(ArgValue);
89 return true;
90 }
91
92
HandleIfExpect(BranchInst * BI)93 bool LowerExpectIntrinsic::HandleIfExpect(BranchInst *BI) {
94 if (BI->isUnconditional())
95 return false;
96
97 // Handle non-optimized IR code like:
98 // %expval = call i64 @llvm.expect.i64(i64 %conv1, i64 1)
99 // %tobool = icmp ne i64 %expval, 0
100 // br i1 %tobool, label %if.then, label %if.end
101 //
102 // Or the following simpler case:
103 // %expval = call i1 @llvm.expect.i1(i1 %cmp, i1 1)
104 // br i1 %expval, label %if.then, label %if.end
105
106 CallInst *CI;
107
108 ICmpInst *CmpI = dyn_cast<ICmpInst>(BI->getCondition());
109 if (!CmpI) {
110 CI = dyn_cast<CallInst>(BI->getCondition());
111 } else {
112 if (CmpI->getPredicate() != CmpInst::ICMP_NE)
113 return false;
114 CI = dyn_cast<CallInst>(CmpI->getOperand(0));
115 }
116
117 if (!CI)
118 return false;
119
120 Function *Fn = CI->getCalledFunction();
121 if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect)
122 return false;
123
124 Value *ArgValue = CI->getArgOperand(0);
125 ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1));
126 if (!ExpectedValue)
127 return false;
128
129 MDBuilder MDB(CI->getContext());
130 MDNode *Node;
131
132 // If expect value is equal to 1 it means that we are more likely to take
133 // branch 0, in other case more likely is branch 1.
134 if (ExpectedValue->isOne())
135 Node = MDB.createBranchWeights(LikelyBranchWeight, UnlikelyBranchWeight);
136 else
137 Node = MDB.createBranchWeights(UnlikelyBranchWeight, LikelyBranchWeight);
138
139 BI->setMetadata(LLVMContext::MD_prof, Node);
140
141 if (CmpI)
142 CmpI->setOperand(0, ArgValue);
143 else
144 BI->setCondition(ArgValue);
145 return true;
146 }
147
148
runOnFunction(Function & F)149 bool LowerExpectIntrinsic::runOnFunction(Function &F) {
150 for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
151 BasicBlock *BB = I++;
152
153 // Create "block_weights" metadata.
154 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
155 if (HandleIfExpect(BI))
156 IfHandled++;
157 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
158 if (HandleSwitchExpect(SI))
159 IfHandled++;
160 }
161
162 // remove llvm.expect intrinsics.
163 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
164 BI != BE; ) {
165 CallInst *CI = dyn_cast<CallInst>(BI++);
166 if (!CI)
167 continue;
168
169 Function *Fn = CI->getCalledFunction();
170 if (Fn && Fn->getIntrinsicID() == Intrinsic::expect) {
171 Value *Exp = CI->getArgOperand(0);
172 CI->replaceAllUsesWith(Exp);
173 CI->eraseFromParent();
174 }
175 }
176 }
177
178 return false;
179 }
180
181
182 char LowerExpectIntrinsic::ID = 0;
183 INITIALIZE_PASS(LowerExpectIntrinsic, "lower-expect", "Lower 'expect' "
184 "Intrinsics", false, false)
185
createLowerExpectIntrinsicPass()186 FunctionPass *llvm::createLowerExpectIntrinsicPass() {
187 return new LowerExpectIntrinsic();
188 }
189