Fold some HW nodes for constant input #78929
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ghost
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch Issue DetailsThis PR setups an initial infrastructure to fold class Prog
{
Vector128<int> Test1() => Vector128.Create(42) | Vector128.Create(1); // is folded to {43;43;43;43}
uint Test2() => Lzcnt.LeadingZeroCount(314); // is folded to 23
}We can extend the list on demand. Main motivation was this case (together with #78783) where I needed
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EgorBo
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@dotnet/jit-contrib @jakobbotsch can you please take a look - I decided to keep only LZCNT for now (because I needed it) and left a space for future foldings on demand including for vectors. |
src/coreclr/jit/valuenum.cpp
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| // E.g. for "Sse2.Or(cnsVec1, cnsVec2)" it looks like this: | ||
| // case NI_SSE2_Or: | ||
| //{ | ||
| // simd16_t v1 = GetConstantSimd16(arg0VN); | ||
| // simd16_t v2 = GetConstantSimd16(arg1VN); | ||
| // v1.i64[0] |= v2.i64[0]; | ||
| // v1.i64[1] |= v2.i64[1]; | ||
| // return VNForSimd16Con(v1); | ||
| //} |
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Is this comment missing some context? Seems out of place
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I left an example of a folding for a binary HWIntrinsic VNFunc for someone who decides to implement it here. (E.g. LLVM folds all vector ops)
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Do you plan to add it? Otherwise I don't really see a reason to create this empty skeleton which might just stay like this forever.
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No near future plans although I did see hits in libraries.pmi for Intrinsics with two VNConstants args.
Ok I'll remove it
ghost
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This PR setups an initial infrastructure to fold
GT_HWINTRINSICnodes for constant input in VN phase. I've added Lzcnt and Or,Xor,And as examples, e.g.:We can extend the list on demand.
Main motivation was this case (together with #78783) where I needed
BitOperations.Log2to be foldable for constant input (uses Lzcnt under the hood):diffs - only in tests for now but I need this for my upcomining optimizations in C#