[llvm] r183802 - [mips] Add an IR transformation pass that optimizes calls to sqrt.
Hal Finkel
hfinkel at anl.gov
Tue Jun 11 15:45:59 PDT 2013
----- Original Message -----
> Author: ahatanak
> Date: Tue Jun 11 17:21:44 2013
> New Revision: 183802
>
> URL: http://llvm.org/viewvc/llvm-project?rev=183802&view=rev
> Log:
> [mips] Add an IR transformation pass that optimizes calls to sqrt.
>
> The pass emits a call to sqrt that has attribute "read-none". This
> call will be
> converted to an ISD::FSQRT node during DAG construction, which will
> turn into
> a mips native sqrt instruction.
This seems almost completely target independent, is there a reason to make this MIPS-specific? Also, is it really better to test the result for NaN as opposed to checking whether the input is negative?
-Hal
>
>
> Added:
> llvm/trunk/lib/Target/Mips/MipsOptimizeMathLibCalls.cpp
> llvm/trunk/test/CodeGen/Mips/optimize-fp-math.ll
> Modified:
> llvm/trunk/lib/Target/Mips/Mips.h
> llvm/trunk/lib/Target/Mips/MipsTargetMachine.cpp
>
> Modified: llvm/trunk/lib/Target/Mips/Mips.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Mips/Mips.h?rev=183802&r1=183801&r2=183802&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/Mips/Mips.h (original)
> +++ llvm/trunk/lib/Target/Mips/Mips.h Tue Jun 11 17:21:44 2013
> @@ -28,7 +28,7 @@ namespace llvm {
> FunctionPass *createMipsJITCodeEmitterPass(MipsTargetMachine &TM,
> JITCodeEmitter &JCE);
> FunctionPass *createMipsConstantIslandPass(MipsTargetMachine &tm);
> -
> + FunctionPass *createMipsOptimizeMathLibCalls(MipsTargetMachine
> &TM);
> } // end namespace llvm;
>
> #endif
>
> Added: llvm/trunk/lib/Target/Mips/MipsOptimizeMathLibCalls.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Mips/MipsOptimizeMathLibCalls.cpp?rev=183802&view=auto
> ==============================================================================
> --- llvm/trunk/lib/Target/Mips/MipsOptimizeMathLibCalls.cpp (added)
> +++ llvm/trunk/lib/Target/Mips/MipsOptimizeMathLibCalls.cpp Tue Jun
> 11 17:21:44 2013
> @@ -0,0 +1,175 @@
> +//===---- MipsOptimizeMathLibCalls.cpp - Optimize math lib calls.
> ----===//
> +//
> +// The LLVM Compiler Infrastructure
> +//
> +// This file is distributed under the University of Illinois Open
> Source
> +// License. See LICENSE.TXT for details.
> +//
> +//===----------------------------------------------------------------------===//
> +//
> +// This pass does an IR transformation which enables the backend to
> emit native
> +// math instructions.
> +//
> +//===----------------------------------------------------------------------===//
> +
> +#include "MipsTargetMachine.h"
> +#include "llvm/IR/IRBuilder.h"
> +#include "llvm/IR/Intrinsics.h"
> +#include "llvm/Pass.h"
> +#include "llvm/Support/CommandLine.h"
> +#include "llvm/Target/TargetLibraryInfo.h"
> +#include "llvm/Transforms/Utils/BasicBlockUtils.h"
> +
> +using namespace llvm;
> +
> +static cl::opt<bool> DisableOpt("disable-mips-math-optimization",
> + cl::init(false),
> + cl::desc("MIPS: Disable math lib
> call "
> + "optimization."),
> cl::Hidden);
> +
> +namespace {
> + class MipsOptimizeMathLibCalls : public FunctionPass {
> + public:
> + static char ID;
> +
> + MipsOptimizeMathLibCalls(MipsTargetMachine &TM_) :
> + FunctionPass(ID), TM(TM_) {}
> +
> + virtual const char *getPassName() const {
> + return "MIPS: Optimize calls to math library functions.";
> + }
> +
> + virtual void getAnalysisUsage(AnalysisUsage &AU) const;
> +
> + virtual bool runOnFunction(Function &F);
> +
> + private:
> + /// Optimize calls to sqrt.
> + bool optimizeSQRT(CallInst *Call, Function *CalledFunc,
> + BasicBlock &CurrBB,
> + Function::iterator &BB);
> +
> + const TargetMachine &TM;
> + };
> +
> + char MipsOptimizeMathLibCalls::ID = 0;
> +}
> +
> +FunctionPass *llvm::createMipsOptimizeMathLibCalls(MipsTargetMachine
> &TM) {
> + return new MipsOptimizeMathLibCalls(TM);
> +}
> +
> +void MipsOptimizeMathLibCalls::getAnalysisUsage(AnalysisUsage &AU)
> const {
> + AU.addRequired<TargetLibraryInfo>();
> + FunctionPass::getAnalysisUsage(AU);
> +}
> +
> +bool MipsOptimizeMathLibCalls::runOnFunction(Function &F) {
> + if (DisableOpt)
> + return false;
> +
> + const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
> +
> + if (Subtarget.inMips16Mode())
> + return false;
> +
> + bool Changed = false;
> + Function::iterator CurrBB;
> + const TargetLibraryInfo *LibInfo =
> &getAnalysis<TargetLibraryInfo>();
> +
> + for (Function::iterator BB = F.begin(), BE = F.end(); BB != BE;) {
> + CurrBB = BB++;
> +
> + for (BasicBlock::iterator II = CurrBB->begin(), IE =
> CurrBB->end();
> + II != IE; ++II) {
> + CallInst *Call = dyn_cast<CallInst>(&*II);
> + Function *CalledFunc;
> +
> + if (!Call || !(CalledFunc = Call->getCalledFunction()))
> + continue;
> +
> + LibFunc::Func LibFunc;
> + Attribute A = CalledFunc->getAttributes()
> + .getAttribute(AttributeSet::FunctionIndex,
> "use-soft-float");
> +
> + // Skip if function has "use-soft-float" attribute.
> + if ((A.isStringAttribute() && (A.getValueAsString() ==
> "true")) ||
> + TM.Options.UseSoftFloat)
> + continue;
> +
> + // Skip if function either has local linkage or is not a known
> library
> + // function.
> + if (CalledFunc->hasLocalLinkage() || !CalledFunc->hasName() ||
> + !LibInfo->getLibFunc(CalledFunc->getName(), LibFunc))
> + continue;
> +
> + switch (LibFunc) {
> + case LibFunc::sqrtf:
> + case LibFunc::sqrt:
> + if (optimizeSQRT(Call, CalledFunc, *CurrBB, BB))
> + break;
> + continue;
> + default:
> + continue;
> + }
> +
> + Changed = true;
> + break;
> + }
> + }
> +
> + return Changed;
> +}
> +
> +bool MipsOptimizeMathLibCalls::optimizeSQRT(CallInst *Call,
> + Function *CalledFunc,
> + BasicBlock &CurrBB,
> + Function::iterator &BB)
> {
> + // There is no need to change the IR, since backend will emit sqrt
> + // instruction if the call has already been marked read-only.
> + if (Call->onlyReadsMemory())
> + return false;
> +
> + // Do the following transformation:
> + //
> + // (before)
> + // dst = sqrt(src)
> + //
> + // (after)
> + // v0 = sqrt_noreadmem(src) # native sqrt instruction.
> + // if (v0 is a NaN)
> + // v1 = sqrt(src) # library call.
> + // dst = phi(v0, v1)
> + //
> +
> + // Move all instructions following Call to newly created block
> JoinBB.
> + // Create phi and replace all uses.
> + BasicBlock *JoinBB = llvm::SplitBlock(&CurrBB,
> Call->getNextNode(), this);
> + IRBuilder<> Builder(JoinBB, JoinBB->begin());
> + PHINode *Phi = Builder.CreatePHI(Call->getType(), 2);
> + Call->replaceAllUsesWith(Phi);
> +
> + // Create basic block LibCallBB and insert a call to library
> function sqrt.
> + BasicBlock *LibCallBB = BasicBlock::Create(CurrBB.getContext(),
> "call.sqrt",
> + CurrBB.getParent(),
> JoinBB);
> + Builder.SetInsertPoint(LibCallBB);
> + Instruction *LibCall = Call->clone();
> + Builder.Insert(LibCall);
> + Builder.CreateBr(JoinBB);
> +
> + // Add attribute "readnone" so that backend can use a native sqrt
> instruction
> + // for this call. Insert a FP compare instruction and a
> conditional branch
> + // at the end of CurrBB.
> + Call->addAttribute(AttributeSet::FunctionIndex,
> Attribute::ReadNone);
> + CurrBB.getTerminator()->eraseFromParent();
> + Builder.SetInsertPoint(&CurrBB);
> + Value *FCmp = Builder.CreateFCmpOEQ(Call, Call);
> + Builder.CreateCondBr(FCmp, JoinBB, LibCallBB);
> +
> + // Add phi operands.
> + Phi->addIncoming(Call, &CurrBB);
> + Phi->addIncoming(LibCall, LibCallBB);
> +
> + BB = JoinBB;
> + return true;
> +}
>
> Modified: llvm/trunk/lib/Target/Mips/MipsTargetMachine.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Mips/MipsTargetMachine.cpp?rev=183802&r1=183801&r2=183802&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/Mips/MipsTargetMachine.cpp (original)
> +++ llvm/trunk/lib/Target/Mips/MipsTargetMachine.cpp Tue Jun 11
> 17:21:44 2013
> @@ -160,6 +160,7 @@ void MipsPassConfig::addIRPasses() {
> addPass(createMipsOs16(getMipsTargetMachine()));
> if (getMipsSubtarget().inMips16HardFloat())
> addPass(createMips16HardFloat(getMipsTargetMachine()));
> + addPass(createMipsOptimizeMathLibCalls(getMipsTargetMachine()));
> }
> // Install an instruction selector pass using
> // the ISelDag to gen Mips code.
>
> Added: llvm/trunk/test/CodeGen/Mips/optimize-fp-math.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/Mips/optimize-fp-math.ll?rev=183802&view=auto
> ==============================================================================
> --- llvm/trunk/test/CodeGen/Mips/optimize-fp-math.ll (added)
> +++ llvm/trunk/test/CodeGen/Mips/optimize-fp-math.ll Tue Jun 11
> 17:21:44 2013
> @@ -0,0 +1,32 @@
> +; RUN: llc -march=mipsel < %s | FileCheck %s -check-prefix=32
> +; RUN: llc -march=mips64el -mcpu=mips64 < %s | FileCheck %s
> -check-prefix=64
> +
> +; 32: test_sqrtf_float_:
> +; 32: sqrt.s $f[[R0:[0-9]+]], $f{{[0-9]+}}
> +; 32: c.un.s $f[[R0]], $f[[R0]]
> +; 64: test_sqrtf_float_:
> +; 64: sqrt.s $f[[R0:[0-9]+]], $f{{[0-9]+}}
> +; 64: c.un.s $f[[R0]], $f[[R0]]
> +
> +define float @test_sqrtf_float_(float %a) {
> +entry:
> + %call = tail call float @sqrtf(float %a)
> + ret float %call
> +}
> +
> +declare float @sqrtf(float)
> +
> +; 32: test_sqrt_double_:
> +; 32: sqrt.d $f[[R0:[0-9]+]], $f{{[0-9]+}}
> +; 32: c.un.d $f[[R0]], $f[[R0]]
> +; 64: test_sqrt_double_:
> +; 64: sqrt.d $f[[R0:[0-9]+]], $f{{[0-9]+}}
> +; 64: c.un.d $f[[R0]], $f[[R0]]
> +
> +define double @test_sqrt_double_(double %a) {
> +entry:
> + %call = tail call double @sqrt(double %a)
> + ret double %call
> +}
> +
> +declare double @sqrt(double)
>
>
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