[llvm] r294288 - Revert "[DAGCombiner] (add X, (adde Y, 0, Carry)) -> (adde X, Y, Carry)"

[Chandler Carruth via llvm-commits]

On Tue, Feb 7, 2017 at 1:09 AM Daniel Jasper via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: djasper
> Date: Tue Feb  7 02:57:50 2017
> New Revision: 294288
>
> URL: http://llvm.org/viewvc/llvm-project?rev=294288&view=rev
> Log:
> Revert "[DAGCombiner] (add X, (adde Y, 0, Carry)) -> (adde X, Y, Carry)"
>
> This reverts commit r294186.
>
> On an internal test, this triggers an out-of-memory error on PPC,
> presumably because there is another dagcombine that does the exact
> opposite triggering and endless loop consuming more and more memory.
>
> Chandler has started at creating a reduced test case and we'll attach it
> as soon as possible.
>

Filed http://llvm.org/PR31890 with an attached test case. It isn't tiny (4k
lines of textual IR) but it is small enough to easily work with and still
reproduces nicely.


>
> Modified:
>     llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>     llvm/trunk/test/CodeGen/X86/adde-carry.ll
>
> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=294288&r1=294287&r2=294288&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
> +++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Tue Feb  7
> 02:57:50 2017
> @@ -1834,12 +1834,6 @@ SDValue DAGCombiner::visitADDLike(SDValu
>      }
>    }
>
> -  // (add X, (adde Y, 0, Carry)) -> (adde X, Y, Carry)
> -  if (N1.getOpcode() == ISD::ADDE && N1->hasOneUse() &&
> -      isNullConstant(N1.getOperand(1)))
> -    return DAG.getNode(ISD::ADDE, DL, DAG.getVTList(VT, MVT::Glue),
> -                       N0, N1->getOperand(0), N1->getOperand(2));
> -
>    return SDValue();
>  }
>
>
> Modified: llvm/trunk/test/CodeGen/X86/adde-carry.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/adde-carry.ll?rev=294288&r1=294287&r2=294288&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/adde-carry.ll (original)
> +++ llvm/trunk/test/CodeGen/X86/adde-carry.ll Tue Feb  7 02:57:50 2017
> @@ -93,16 +93,17 @@ define %scalar @pr31719(%scalar* nocaptu
>  ; CHECK-NEXT:    sbbq %r10, %r10
>  ; CHECK-NEXT:    andl $1, %r10d
>  ; CHECK-NEXT:    addq 8(%rsi), %rcx
> +; CHECK-NEXT:    sbbq %r11, %r11
> +; CHECK-NEXT:    andl $1, %r11d
> +; CHECK-NEXT:    addq %r10, %rcx
> +; CHECK-NEXT:    adcq $0, %r11
> +; CHECK-NEXT:    addq 16(%rsi), %r8
>  ; CHECK-NEXT:    sbbq %rax, %rax
>  ; CHECK-NEXT:    andl $1, %eax
> -; CHECK-NEXT:    addq %r10, %rcx
> +; CHECK-NEXT:    addq %r11, %r8
>  ; CHECK-NEXT:    adcq $0, %rax
> -; CHECK-NEXT:    addq 16(%rsi), %r8
> -; CHECK-NEXT:    sbbq %r10, %r10
> -; CHECK-NEXT:    andl $1, %r10d
>  ; CHECK-NEXT:    addq 24(%rsi), %r9
> -; CHECK-NEXT:    addq %rax, %r8
> -; CHECK-NEXT:    adcq %r10, %r9
> +; CHECK-NEXT:    addq %rax, %r9
>  ; CHECK-NEXT:    movq %rdx, (%rdi)
>  ; CHECK-NEXT:    movq %rcx, 8(%rdi)
>  ; CHECK-NEXT:    movq %r8, 16(%rdi)
>
>
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