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

[David Majnemer]

Yes, Nick LGTM'd this. See
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140512/217399.htmlfor
details.


On Fri, May 16, 2014 at 4:08 PM, Sean Silva <chisophugis at gmail.com> wrote:

> 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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>>
>
>
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