[llvm] r208827 - InstCombine: Optimize -x s< cst

[Sean Silva]

Did Nick ever LGTM this? The phab revision seems to not have had any
movement.

-- Sean Silva


On Wed, May 14, 2014 at 6:02 PM, David Majnemer <david.majnemer at gmail.com>wrote:

> Author: majnemer
> Date: Wed May 14 19:02:20 2014
> New Revision: 208827
>
> URL: http://llvm.org/viewvc/llvm-project?rev=208827&view=rev
> Log:
> InstCombine: Optimize -x s< cst
>
> Summary:
> This gets rid of a sub instruction by moving the negation to the
> constant when valid.
>
> Reviewers: nicholas
>
> Subscribers: llvm-commits
>
> Differential Revision: http://reviews.llvm.org/D3773
>
> Modified:
>     llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>     llvm/trunk/test/Transforms/InstCombine/icmp.ll
>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=208827&r1=208826&r2=208827&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
> (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Wed May
> 14 19:02:20 2014
> @@ -2971,6 +2971,16 @@ Instruction *InstCombiner::visitICmpInst
>          BO0->hasOneUse() && BO1->hasOneUse())
>        return new ICmpInst(Pred, D, B);
>
> +    // icmp (0-X) < cst --> x > -cst
> +    if (NoOp0WrapProblem && ICmpInst::isSigned(Pred)) {
> +      Value *X;
> +      if (match(BO0, m_Neg(m_Value(X))))
> +        if (ConstantInt *RHSC = dyn_cast<ConstantInt>(Op1))
> +          if (!RHSC->isMinValue(/*isSigned=*/true))
> +            return new ICmpInst(I.getSwappedPredicate(), X,
> +                                ConstantExpr::getNeg(RHSC));
> +    }
> +
>      BinaryOperator *SRem = nullptr;
>      // icmp (srem X, Y), Y
>      if (BO0 && BO0->getOpcode() == Instruction::SRem &&
>
> Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=208827&r1=208826&r2=208827&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Wed May 14 19:02:20 2014
> @@ -1356,3 +1356,12 @@ define i1 @icmp_ashr_ashr_ne(i32 %a, i32
>   %z = icmp ne i32 %x, %y
>   ret i1 %z
>  }
> +
> +; CHECK-LABEL: @icmp_neg_cst_slt
> +; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp sgt i32 %a, 10
> +; CHECK-NEXT: ret i1 [[CMP]]
> +define i1 @icmp_neg_cst_slt(i32 %a) {
> +  %1 = sub nsw i32 0, %a
> +  %2 = icmp slt i32 %1, -10
> +  ret i1 %2
> +}
>
>
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