[llvm-commits] [llvm] r156323 - in /llvm/trunk: lib/Transforms/Scalar/Reassociate.cpp test/Transforms/Reassociate/fp-commute.ll

[Duncan Sands]

Hi Owen,

> Teach reassociate to commute FMul's and FAdd's in order to canonicalize the order of their operands across instructions.  This allows for greater CSE opportunities.

this doesn't really have anything to do with reassociation...  so why put it
here?  Is it because you want to use getRank?  Instcombine has getComplexity -
maybe that should be boosted instead?  Is it that getRank is too expensive for
instcombine?

Ciao, Duncan.

>
> Added:
>      llvm/trunk/test/Transforms/Reassociate/fp-commute.ll
> Modified:
>      llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp?rev=156323&r1=156322&r2=156323&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/Reassociate.cpp Mon May  7 15:47:23 2012
> @@ -1212,10 +1212,34 @@
>         BI = NI;
>       }
>
> -  // Reject cases where it is pointless to do this.
> -  if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPointTy() ||
> -      BI->getType()->isVectorTy())
> -    return;  // Floating point ops are not associative.
> +  // Floating point binary operators are not associative, but we can still
> +  // commute (some) of them, to canonicalize the order of their operands.
> +  // This can potentially expose more CSE opportunities, and makes writing
> +  // other transformations simpler.
> +  if (isa<BinaryOperator>(BI)&&
> +      (BI->getType()->isFloatingPointTy() || BI->getType()->isVectorTy())) {
> +    // FAdd and FMul can be commuted.
> +    if (BI->getOpcode() != Instruction::FMul&&
> +        BI->getOpcode() != Instruction::FAdd)
> +      return;
> +
> +    Value *LHS = BI->getOperand(0);
> +    Value *RHS = BI->getOperand(1);
> +    unsigned LHSRank = getRank(LHS);
> +    unsigned RHSRank = getRank(RHS);
> +
> +    // Sort the operands by rank.
> +    if (RHSRank<  LHSRank) {
> +      BI->setOperand(0, RHS);
> +      BI->setOperand(1, LHS);
> +    }
> +
> +    return;
> +  }
> +
> +  // Do not reassociate operations that we do not understand.
> +  if (!isa<BinaryOperator>(BI))
> +    return;
>
>     // Do not reassociate boolean (i1) expressions.  We want to preserve the
>     // original order of evaluation for short-circuited comparisons that
>
> Added: llvm/trunk/test/Transforms/Reassociate/fp-commute.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Reassociate/fp-commute.ll?rev=156323&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/Reassociate/fp-commute.ll (added)
> +++ llvm/trunk/test/Transforms/Reassociate/fp-commute.ll Mon May  7 15:47:23 2012
> @@ -0,0 +1,16 @@
> +; RUN: opt -reassociate -S<  %s | FileCheck %s
> +
> +target triple = "armv7-apple-ios"
> +
> +; CHECK: test
> +define float @test(float %x, float %y) {
> +entry:
> +; CHECK: fmul float %x, %y
> +; CHECK: fmul float %x, %y
> +  %0 = fmul float %x, %y
> +  %1 = fmul float %y, %x
> +  %2 = fsub float %0, %1
> +  ret float %1
> +}
> +
> +
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits