1 //===--- PartiallyInlineLibCalls.cpp - Partially inline libcalls ----------===//
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 tries to partially inline the fast path of well-known library
11 // functions, such as using square-root instructions for cases where sqrt()
12 // does not need to set errno.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #include "llvm/Analysis/TargetTransformInfo.h"
17 #include "llvm/IR/IRBuilder.h"
18 #include "llvm/IR/Intrinsics.h"
19 #include "llvm/Pass.h"
20 #include "llvm/Support/CommandLine.h"
21 #include "llvm/Target/TargetLibraryInfo.h"
22 #include "llvm/Transforms/Scalar.h"
23 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
24
25 using namespace llvm;
26
27 #define DEBUG_TYPE "partially-inline-libcalls"
28
29 namespace {
30 class PartiallyInlineLibCalls : public FunctionPass {
31 public:
32 static char ID;
33
PartiallyInlineLibCalls()34 PartiallyInlineLibCalls() :
35 FunctionPass(ID) {
36 initializePartiallyInlineLibCallsPass(*PassRegistry::getPassRegistry());
37 }
38
39 void getAnalysisUsage(AnalysisUsage &AU) const override;
40 bool runOnFunction(Function &F) override;
41
42 private:
43 /// Optimize calls to sqrt.
44 bool optimizeSQRT(CallInst *Call, Function *CalledFunc,
45 BasicBlock &CurrBB, Function::iterator &BB);
46 };
47
48 char PartiallyInlineLibCalls::ID = 0;
49 }
50
51 INITIALIZE_PASS(PartiallyInlineLibCalls, "partially-inline-libcalls",
52 "Partially inline calls to library functions", false, false)
53
getAnalysisUsage(AnalysisUsage & AU) const54 void PartiallyInlineLibCalls::getAnalysisUsage(AnalysisUsage &AU) const {
55 AU.addRequired<TargetLibraryInfo>();
56 AU.addRequired<TargetTransformInfo>();
57 FunctionPass::getAnalysisUsage(AU);
58 }
59
runOnFunction(Function & F)60 bool PartiallyInlineLibCalls::runOnFunction(Function &F) {
61 bool Changed = false;
62 Function::iterator CurrBB;
63 TargetLibraryInfo *TLI = &getAnalysis<TargetLibraryInfo>();
64 const TargetTransformInfo *TTI = &getAnalysis<TargetTransformInfo>();
65 for (Function::iterator BB = F.begin(), BE = F.end(); BB != BE;) {
66 CurrBB = BB++;
67
68 for (BasicBlock::iterator II = CurrBB->begin(), IE = CurrBB->end();
69 II != IE; ++II) {
70 CallInst *Call = dyn_cast<CallInst>(&*II);
71 Function *CalledFunc;
72
73 if (!Call || !(CalledFunc = Call->getCalledFunction()))
74 continue;
75
76 // Skip if function either has local linkage or is not a known library
77 // function.
78 LibFunc::Func LibFunc;
79 if (CalledFunc->hasLocalLinkage() || !CalledFunc->hasName() ||
80 !TLI->getLibFunc(CalledFunc->getName(), LibFunc))
81 continue;
82
83 switch (LibFunc) {
84 case LibFunc::sqrtf:
85 case LibFunc::sqrt:
86 if (TTI->haveFastSqrt(Call->getType()) &&
87 optimizeSQRT(Call, CalledFunc, *CurrBB, BB))
88 break;
89 continue;
90 default:
91 continue;
92 }
93
94 Changed = true;
95 break;
96 }
97 }
98
99 return Changed;
100 }
101
optimizeSQRT(CallInst * Call,Function * CalledFunc,BasicBlock & CurrBB,Function::iterator & BB)102 bool PartiallyInlineLibCalls::optimizeSQRT(CallInst *Call,
103 Function *CalledFunc,
104 BasicBlock &CurrBB,
105 Function::iterator &BB) {
106 // There is no need to change the IR, since backend will emit sqrt
107 // instruction if the call has already been marked read-only.
108 if (Call->onlyReadsMemory())
109 return false;
110
111 // Do the following transformation:
112 //
113 // (before)
114 // dst = sqrt(src)
115 //
116 // (after)
117 // v0 = sqrt_noreadmem(src) # native sqrt instruction.
118 // if (v0 is a NaN)
119 // v1 = sqrt(src) # library call.
120 // dst = phi(v0, v1)
121 //
122
123 // Move all instructions following Call to newly created block JoinBB.
124 // Create phi and replace all uses.
125 BasicBlock *JoinBB = llvm::SplitBlock(&CurrBB, Call->getNextNode(), this);
126 IRBuilder<> Builder(JoinBB, JoinBB->begin());
127 PHINode *Phi = Builder.CreatePHI(Call->getType(), 2);
128 Call->replaceAllUsesWith(Phi);
129
130 // Create basic block LibCallBB and insert a call to library function sqrt.
131 BasicBlock *LibCallBB = BasicBlock::Create(CurrBB.getContext(), "call.sqrt",
132 CurrBB.getParent(), JoinBB);
133 Builder.SetInsertPoint(LibCallBB);
134 Instruction *LibCall = Call->clone();
135 Builder.Insert(LibCall);
136 Builder.CreateBr(JoinBB);
137
138 // Add attribute "readnone" so that backend can use a native sqrt instruction
139 // for this call. Insert a FP compare instruction and a conditional branch
140 // at the end of CurrBB.
141 Call->addAttribute(AttributeSet::FunctionIndex, Attribute::ReadNone);
142 CurrBB.getTerminator()->eraseFromParent();
143 Builder.SetInsertPoint(&CurrBB);
144 Value *FCmp = Builder.CreateFCmpOEQ(Call, Call);
145 Builder.CreateCondBr(FCmp, JoinBB, LibCallBB);
146
147 // Add phi operands.
148 Phi->addIncoming(Call, &CurrBB);
149 Phi->addIncoming(LibCall, LibCallBB);
150
151 BB = JoinBB;
152 return true;
153 }
154
createPartiallyInlineLibCallsPass()155 FunctionPass *llvm::createPartiallyInlineLibCallsPass() {
156 return new PartiallyInlineLibCalls();
157 }
158