[llvm-dev] i1 true ^= -1 in DAG matcher?

[Hendrik Greving via llvm-dev]

Yes the cited FIXME code might be unrelated. I do think there is _some_
kind of issue somewhere because I do see a BUILD_VECTOR of i1 -1 on our
target which I set to setBooleanVectorContents(ZeroOrOneBooleanContent).
The backend is not open source, but the i1 vector is an input to a clang
builtin which takes V8i like
__builtin_special(~mask) where mask is an vector of i1 form a setne (cmp),
and the vector of i1 -1 is from the ~ that does an xor of those two
vectors. I would have expected a vector of 1, not -1. I would love to send
in a better open source reproducer, will try to construct one.

On Wed, Feb 19, 2020 at 11:30 AM Craig Topper <craig.topper at gmail.com>
wrote:

> The vnot PatFrag uses ImmAllOnesV which should put an OPC_CheckImmAllOnesV
> in the matcher table. And the matcher table should call
> ISD::isBuildVectorAllOnes. I believe we use vnot with vXi1 vectors on X86
> and I haven't seen any issues.
>
> The FIXME you pointed to seems related to a scalar patcher not a vector
> pattern. In that case the issue is that the immediate matcher for scalars
> calls getSExtValue on a 1-bit APInt which will return -1 in an int64_t.
>
> ~Craig
>
>
> On Wed, Feb 19, 2020 at 11:11 AM Tim Northover via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi Hendrik,
>>
>> On Wed, 19 Feb 2020 at 11:01, Hendrik Greving via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>> > It looks like that in the DAG matcher, the DAG has a xor with '-1' for
>> checking a true value vector
>> >
>> > for instance,
>> >
>> > %cmp4.i = icmp ne <8 x i32> %6, %5
>> > %7 = xor <8 x i1> %cmp4.i, <i1 true, i1 true, i1 true, i1 true, i1
>> true, i1 true, i1 true, i1 true>
>> > [use of %7]
>> >
>> > results in vector of  '-1' in the DAG.
>>
>> This should be controlled by TargetLowering::setBooleanVectorContents,
>> which lets each target choose whether a boolean is 0/1 or 0/-1 when
>> held in a larger register. For AMDGPU it looks like R600 wants 0/-1,
>> but SIL wants 0/1 so if you're seeing -1 when compiling for a SIL
>> target that's probably a bug.
>>
>> Cheers.
>>
>> Tim.
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>
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