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
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
|
//===- LowerExpectIntrinsic.cpp - Lower expect intrinsic ------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass lowers the 'expect' intrinsic to LLVM metadata.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/LowerExpectIntrinsic.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Metadata.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Scalar.h"
using namespace llvm;
#define DEBUG_TYPE "lower-expect-intrinsic"
STATISTIC(ExpectIntrinsicsHandled,
"Number of 'expect' intrinsic instructions handled");
static cl::opt<uint32_t>
LikelyBranchWeight("likely-branch-weight", cl::Hidden, cl::init(64),
cl::desc("Weight of the branch likely to be taken (default = 64)"));
static cl::opt<uint32_t>
UnlikelyBranchWeight("unlikely-branch-weight", cl::Hidden, cl::init(4),
cl::desc("Weight of the branch unlikely to be taken (default = 4)"));
static bool handleSwitchExpect(SwitchInst &SI) {
CallInst *CI = dyn_cast<CallInst>(SI.getCondition());
if (!CI)
return false;
Function *Fn = CI->getCalledFunction();
if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect)
return false;
Value *ArgValue = CI->getArgOperand(0);
ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1));
if (!ExpectedValue)
return false;
SwitchInst::CaseIt Case = SI.findCaseValue(ExpectedValue);
unsigned n = SI.getNumCases(); // +1 for default case.
SmallVector<uint32_t, 16> Weights(n + 1, UnlikelyBranchWeight);
if (Case == SI.case_default())
Weights[0] = LikelyBranchWeight;
else
Weights[Case.getCaseIndex() + 1] = LikelyBranchWeight;
SI.setMetadata(LLVMContext::MD_prof,
MDBuilder(CI->getContext()).createBranchWeights(Weights));
SI.setCondition(ArgValue);
return true;
}
static bool handleBranchExpect(BranchInst &BI) {
if (BI.isUnconditional())
return false;
// Handle non-optimized IR code like:
// %expval = call i64 @llvm.expect.i64(i64 %conv1, i64 1)
// %tobool = icmp ne i64 %expval, 0
// br i1 %tobool, label %if.then, label %if.end
//
// Or the following simpler case:
// %expval = call i1 @llvm.expect.i1(i1 %cmp, i1 1)
// br i1 %expval, label %if.then, label %if.end
CallInst *CI;
ICmpInst *CmpI = dyn_cast<ICmpInst>(BI.getCondition());
if (!CmpI) {
CI = dyn_cast<CallInst>(BI.getCondition());
} else {
if (CmpI->getPredicate() != CmpInst::ICMP_NE)
return false;
CI = dyn_cast<CallInst>(CmpI->getOperand(0));
}
if (!CI)
return false;
Function *Fn = CI->getCalledFunction();
if (!Fn || Fn->getIntrinsicID() != Intrinsic::expect)
return false;
Value *ArgValue = CI->getArgOperand(0);
ConstantInt *ExpectedValue = dyn_cast<ConstantInt>(CI->getArgOperand(1));
if (!ExpectedValue)
return false;
MDBuilder MDB(CI->getContext());
MDNode *Node;
// If expect value is equal to 1 it means that we are more likely to take
// branch 0, in other case more likely is branch 1.
if (ExpectedValue->isOne())
Node = MDB.createBranchWeights(LikelyBranchWeight, UnlikelyBranchWeight);
else
Node = MDB.createBranchWeights(UnlikelyBranchWeight, LikelyBranchWeight);
BI.setMetadata(LLVMContext::MD_prof, Node);
if (CmpI)
CmpI->setOperand(0, ArgValue);
else
BI.setCondition(ArgValue);
return true;
}
static bool lowerExpectIntrinsic(Function &F) {
bool Changed = false;
for (BasicBlock &BB : F) {
// Create "block_weights" metadata.
if (BranchInst *BI = dyn_cast<BranchInst>(BB.getTerminator())) {
if (handleBranchExpect(*BI))
ExpectIntrinsicsHandled++;
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB.getTerminator())) {
if (handleSwitchExpect(*SI))
ExpectIntrinsicsHandled++;
}
// remove llvm.expect intrinsics.
for (BasicBlock::iterator BI = BB.begin(), BE = BB.end(); BI != BE;) {
CallInst *CI = dyn_cast<CallInst>(BI++);
if (!CI)
continue;
Function *Fn = CI->getCalledFunction();
if (Fn && Fn->getIntrinsicID() == Intrinsic::expect) {
Value *Exp = CI->getArgOperand(0);
CI->replaceAllUsesWith(Exp);
CI->eraseFromParent();
Changed = true;
}
}
}
return Changed;
}
PreservedAnalyses LowerExpectIntrinsicPass::run(Function &F) {
if (lowerExpectIntrinsic(F))
return PreservedAnalyses::none();
return PreservedAnalyses::all();
}
namespace {
/// \brief Legacy pass for lowering expect intrinsics out of the IR.
///
/// When this pass is run over a function it uses expect intrinsics which feed
/// branches and switches to provide branch weight metadata for those
/// terminators. It then removes the expect intrinsics from the IR so the rest
/// of the optimizer can ignore them.
class LowerExpectIntrinsic : public FunctionPass {
public:
static char ID;
LowerExpectIntrinsic() : FunctionPass(ID) {
initializeLowerExpectIntrinsicPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override { return lowerExpectIntrinsic(F); }
};
}
char LowerExpectIntrinsic::ID = 0;
INITIALIZE_PASS(LowerExpectIntrinsic, "lower-expect",
"Lower 'expect' Intrinsics", false, false)
FunctionPass *llvm::createLowerExpectIntrinsicPass() {
return new LowerExpectIntrinsic();
}
|
