[llvm] r285480 - [DAGCombiner] Fix a crash visiting `AND` nodes.

[Manuel Klimek via llvm-commits]

On Sat, Oct 29, 2016 at 2:04 AM Davide Italiano via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: davide
> Date: Fri Oct 28 18:55:32 2016
> New Revision: 285480
>
> URL: http://llvm.org/viewvc/llvm-project?rev=285480&view=rev
> Log:
> [DAGCombiner] Fix a crash visiting `AND` nodes.
>
> Instead of asserting that the shift count is != 0 we just bail out
> as it's not profitable trying to optimize a node which will be
> removed anyway.
>
> Differential Revision:  https://reviews.llvm.org/D26098
>
> Added:
>     llvm/trunk/test/CodeGen/X86/pr30813.s
> Modified:
>     llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>
> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=285480&r1=285479&r2=285480&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
> +++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Fri Oct 28
> 18:55:32 2016
> @@ -3046,6 +3046,11 @@ SDValue DAGCombiner::visitANDLike(SDValu
>          unsigned Size = VT.getSizeInBits();
>          const APInt &AndMask = CAnd->getAPIntValue();
>          unsigned ShiftBits = CShift->getZExtValue();
> +
> +        // Bail out, this node will probably disappear anyway.
> +        if (ShiftBits == 0)
> +          return SDValue();
> +
>          unsigned MaskBits = AndMask.countTrailingOnes();
>          EVT HalfVT = EVT::getIntegerVT(*DAG.getContext(), Size / 2);
>
> @@ -3064,7 +3069,7 @@ SDValue DAGCombiner::visitANDLike(SDValu
>            // extended to handle extensions mixed in.
>
>            SDValue SL(N0);
> -          assert(ShiftBits != 0 && MaskBits <= Size);
> +          assert(MaskBits <= Size);
>
>            // Extracting the highest bit of the low half.
>            EVT ShiftVT = TLI.getShiftAmountTy(HalfVT, DAG.getDataLayout());
>
> Added: llvm/trunk/test/CodeGen/X86/pr30813.s
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/pr30813.s?rev=285480&view=auto
>
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/pr30813.s (added)
>

This file doesn't have a RUN line, and I think .s files in this directory
are not executed by default anyway - am I holding it wrong, or did you
intend to submit a different file?


> +++ llvm/trunk/test/CodeGen/X86/pr30813.s Fri Oct 28 18:55:32 2016
> @@ -0,0 +1,20 @@
> +       .text
> +       .file   "/home/davide/work/llvm/test/CodeGen/X86/visitand-shift.ll"
> +       .globl  patatino
> +       .p2align        4, 0x90
> +       .type   patatino, at function
> +patatino:                               # @patatino
> +       .cfi_startproc
> +# BB#0:
> +                                        # implicit-def: %RAX
> +       movzwl  (%rax), %ecx
> +       movl    %ecx, %eax
> +                                        # implicit-def: %RDX
> +       movq    %rax, (%rdx)
> +       retq
> +.Lfunc_end0:
> +       .size   patatino, .Lfunc_end0-patatino
> +       .cfi_endproc
> +
> +
> +       .section        ".note.GNU-stack","", at progbits
>
>
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