[llvm] r183802 - [mips] Add an IR transformation pass that optimizes calls to sqrt.
Evan Cheng
evan.cheng at apple.com
Fri Jun 14 10:27:43 PDT 2013
Yes, I think we should discuss it. Now that LLVM IR level transformation passes are allowed target data / hooks, we should explore the possibilities of allowing target specific lowering at this level. I think it's ok for the patch to stay as it is for now. But I'd like to see a discussion to migrate over to simplifylibcalls.
Evan
On Jun 12, 2013, at 10:08 PM, Eric Christopher <echristo at gmail.com> wrote:
> 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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