[llvm-dev] i1 true ^= -1 in DAG matcher? (original) (raw)
Hendrik Greving via llvm-dev llvm-dev at lists.llvm.org
Wed Feb 19 11:01:13 PST 2020
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Hello,
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 also seems the reason why LLVM's vnot PatFrag doesn't match in this case. I've also found f rom third_party/llvm/llvm-project/llvm/lib/Target/AMDGPU/SIInstructions.td:
// FIXME: The generated DAG matcher seems to have strange behavior // with a 1-bit literal to match, so use a -1 for checking a true // 1-bit value.
Which seems to reflect the same observation. Is this a bug or a feature?
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