probinson added inline comments.
================ Comment at: clang/lib/Headers/avx2intrin.h:3474 +/// IF __M[j+31] == 1 +/// result[j+31:j] := Load32(__X+(i*4)) +/// ELSE ---------------- pengfei wrote: > probinson wrote: > > pengfei wrote: > > > probinson wrote: > > > > pengfei wrote: > > > > > A more intrinsic guide format is `MEM[__X+j:j]` > > > > LoadXX is the syntax in the gather intrinsics, e.g. > > > > _mm_mask_i32gather_pd. I'd prefer to be consistent. > > > I think the problem here is the measurement is easily confusing. > > > From C point of view, `__X` is a `int` pointer, so we should `+ i` rather > > > than `i * 4` > > > From the other part of the code, we are measuring in bits, but here `i * > > > 4` is a byte offset. > > Well, the pseudo-code is clearly not C. If you look at the gather code, it > > computes a byte address using an offset multiplied by an explicit scale > > factor. I am doing exactly the same here. > > > > The syntax `MEM[__X+j:j]` is mixing a byte address with a bit offset, which > > I think is more confusing. To be fully consistent, using `[]` with bit > > offsets only, it should be > > ``` > > k := __X*8 + i*32 > > result[j+31:j] := MEM[k+31:k] > > ``` > > which I think obscures more than it explains. > Yeah, it's not C code here. But we are easy to fall into C concepts, e.g., > why assuming __X is measuring in bytes? > That's why I think it's clear to make both in bits. > I made a mistake here, I wanted to propose `MEM[__X+j+31: __X+j]`. It matches > with [[ > https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#ig_expand=4057,4058,4059,4053,665,3890,5959,5910,3870,4280&text=_mm256_maskload_epi32 > | Intrinsic Guide ]]. > We assume `__X` is in bytes because that's how addresses work on X86. Adding a bit offset to a byte address makes no sense. I see that is how existing Intel documentation works, which does not make it correct. To "make both in bits" means multiplying `__X` by 8, as in the example in my previous comment. Or coming up with a different syntax that makes the difference clear. `MEM(__X)[j+31:j]` or even `MEM[__X][j+31:j]` would be preferable. CHANGES SINCE LAST ACTION https://reviews.llvm.org/D153993/new/ https://reviews.llvm.org/D153993 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
