[llvm] r183802 - [mips] Add an IR transformation pass that optimizes calls to sqrt.
Eric Christopher
echristo at gmail.com
Wed Jun 12 22:08:33 PDT 2013
We already have a libcall simplification pass - I think it's
reasonably obvious that at least this should be proposed there first
before being committed into the mips backend.
-eric
On Tue, Jun 11, 2013 at 4:06 PM, Akira Hatanaka <ahatanak at gmail.com> wrote:
> I was simply copying what gcc was doing. As you've pointed out, you can
> check if the input is negative first. The difference is that you'll have to
> emit one more branch (not sure how much difference this will make to
> performance):
>
> if (input is negative)
> libcall
> else
> native instruction
>
>
> (transformation in this patch):
>
> native_instruction
>
> if (result is nan)
> libcall
>
> I made this pass mips-specific because I was planning to commit another
> patch which does a mips-specific optimization to calls to other math library
> calls (ceil, trunc and trunc), but there isn't any reason the transformation
> in this patch can't be target independent.
>
>
>
> On Tue, Jun 11, 2013 at 3:45 PM, Hal Finkel <hfinkel at anl.gov> wrote:
>>
>> ----- 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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