lib/Transforms/Scalar/PartiallyInlineLibCalls.cpp

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