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      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 
     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 
     54 void PartiallyInlineLibCalls::getAnalysisUsage(AnalysisUsage &AU) const {
     55   AU.addRequired<TargetLibraryInfo>();
     56   AU.addRequired<TargetTransformInfo>();
     57   FunctionPass::getAnalysisUsage(AU);
     58 }
     59 
     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 
    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 
    155 FunctionPass *llvm::createPartiallyInlineLibCallsPass() {
    156   return new PartiallyInlineLibCalls();
    157 }
    158