[llvm-commits] [llvm] r85144 - in /llvm/trunk: include/llvm/LinkAllPasses.h include/llvm/Transforms/Scalar.h lib/Transforms/Scalar/GEPSplitter.cpp

[Owen Anderson]

On Oct 26, 2009, at 12:12 PM, Dan Gohman wrote:

> Author: djg
> Date: Mon Oct 26 14:12:14 2009
> New Revision: 85144
>
> URL: http://llvm.org/viewvc/llvm-project?rev=85144&view=rev
> Log:
> Check in the experimental GEP splitter pass. This pass splits complex
> GEPs (more than one non-zero index) into simple GEPs (at most one
> non-zero index).  In some simple experiments using this it's not
> uncommon to see 3% overall code size wins, because it exposes
> redundancies that can be eliminated, however it's tricky to use
> because instcombine aggressively undoes the work that this pass does.
>


How about running it right before GVN, and letting a later instcombine  
pass clean it up?

--Owen

> Added:
>  llvm/trunk/lib/Transforms/Scalar/GEPSplitter.cpp
> Modified:
>  llvm/trunk/include/llvm/LinkAllPasses.h
>  llvm/trunk/include/llvm/Transforms/Scalar.h
>
> Modified: llvm/trunk/include/llvm/LinkAllPasses.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/LinkAllPasses.h?rev=85144&r1=85143&r2=85144&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/include/llvm/LinkAllPasses.h (original)
> +++ llvm/trunk/include/llvm/LinkAllPasses.h Mon Oct 26 14:12:14 2009
> @@ -141,6 +141,7 @@
>     (void) llvm::createPartialInliningPass();
>     (void) llvm::createSSIPass();
>     (void) llvm::createSSIEverythingPass();
> +      (void) llvm::createGEPSplitterPass();
>
>     (void)new llvm::IntervalPartition();
>     (void)new llvm::FindUsedTypes();
>
> Modified: llvm/trunk/include/llvm/Transforms/Scalar.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Scalar.h?rev=85144&r1=85143&r2=85144&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/include/llvm/Transforms/Scalar.h (original)
> +++ llvm/trunk/include/llvm/Transforms/Scalar.h Mon Oct 26 14:12:14  
> 2009
> @@ -341,6 +341,12 @@
> //
> FunctionPass *createSSIEverythingPass();
>
> +// 
> = 
> = 
> = 
> ----------------------------------------------------------------------= 
> ==//
> +//
> +// GEPSplitter - Split complex GEPs into simple ones
> +//
> +FunctionPass *createGEPSplitterPass();
> +
> } // End llvm namespace
>
> #endif
>
> Added: llvm/trunk/lib/Transforms/Scalar/GEPSplitter.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GEPSplitter.cpp?rev=85144&view=auto
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/lib/Transforms/Scalar/GEPSplitter.cpp (added)
> +++ llvm/trunk/lib/Transforms/Scalar/GEPSplitter.cpp Mon Oct 26  
> 14:12:14 2009
> @@ -0,0 +1,81 @@
> +//===- GEPSplitter.cpp - Split complex GEPs into simple ones  
> --------------===//
> +//
> +//                     The LLVM Compiler Infrastructure
> +//
> +// This file is distributed under the University of Illinois Open  
> Source
> +// License. See LICENSE.TXT for details.
> +//
> +// 
> = 
> = 
> = 
> ----------------------------------------------------------------------= 
> ==//
> +//
> +// This function breaks GEPs with more than 2 non-zero operands  
> into smaller
> +// GEPs each with no more than 2 non-zero operands. This exposes  
> redundancy
> +// between GEPs with common initial operand sequences.
> +//
> +// 
> = 
> = 
> = 
> ----------------------------------------------------------------------= 
> ==//
> +
> +#define DEBUG_TYPE "split-geps"
> +#include "llvm/Transforms/Scalar.h"
> +#include "llvm/Constants.h"
> +#include "llvm/Function.h"
> +#include "llvm/Instructions.h"
> +#include "llvm/Pass.h"
> +using namespace llvm;
> +
> +namespace {
> +  class GEPSplitter : public FunctionPass {
> +    virtual bool runOnFunction(Function &F);
> +    virtual void getAnalysisUsage(AnalysisUsage &AU) const;
> +  public:
> +    static char ID; // Pass identification, replacement for typeid
> +    explicit GEPSplitter() : FunctionPass(&ID) {}
> +  };
> +}
> +
> +char GEPSplitter::ID = 0;
> +static RegisterPass<GEPSplitter> X("split-geps",
> +                                   "split complex GEPs into simple  
> GEPs");
> +
> +FunctionPass *llvm::createGEPSplitterPass() {
> +  return new GEPSplitter();
> +}
> +
> +bool GEPSplitter::runOnFunction(Function &F) {
> +  bool Changed = false;
> +
> +  // Visit each GEP instruction.
> +  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
> +    for (BasicBlock::iterator II = I->begin(), IE = I->end(); II !=  
> IE; )
> +      if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(II+ 
> +)) {
> +        unsigned NumOps = GEP->getNumOperands();
> +        // Ignore GEPs which are already simple.
> +        if (NumOps <= 2)
> +          continue;
> +        bool FirstIndexIsZero = isa<ConstantInt>(GEP->getOperand 
> (1)) &&
> +                                cast<ConstantInt>(GEP->getOperand 
> (1))->isZero();
> +        if (NumOps == 3 && FirstIndexIsZero)
> +          continue;
> +        // The first index is special and gets expanded with a 2- 
> operand GEP
> +        // (unless it's zero, in which case we can skip this).
> +        Value *NewGEP = FirstIndexIsZero ?
> +          GEP->getOperand(0) :
> +          GetElementPtrInst::Create(GEP->getOperand(0), GEP- 
> >getOperand(1),
> +                                    "tmp", GEP);
> +        // All remaining indices get expanded with a 3-operand GEP  
> with zero
> +        // as the second operand.
> +        Value *Idxs[2];
> +        Idxs[0] = ConstantInt::get(Type::getInt64Ty(F.getContext 
> ()), 0);
> +        for (unsigned i = 2; i != NumOps; ++i) {
> +          Idxs[1] = GEP->getOperand(i);
> +          NewGEP = GetElementPtrInst::Create(NewGEP, Idxs, Idxs+2,  
> "tmp", GEP);
> +        }
> +        GEP->replaceAllUsesWith(NewGEP);
> +        GEP->eraseFromParent();
> +        Changed = true;
> +      }
> +
> +  return Changed;
> +}
> +
> +void GEPSplitter::getAnalysisUsage(AnalysisUsage &AU) const {
> +  AU.setPreservesCFG();
> +}
>
>
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