pengfei added inline comments.
================
Comment at: clang/lib/Headers/avx512vlbf16intrin.h:416
/// and fraction field is truncated to 7 bits.
-static __inline__ __bfloat16 __DEFAULT_FN_ATTRS128 _mm_cvtness_sbh(float __A) {
+static __inline__ short __DEFAULT_FN_ATTRS128 _mm_cvtness_sbh(float __A) {
__v4sf __V = {__A, 0, 0, 0};
----------------
FreddyYe wrote:
> craig.topper wrote:
> > I'm not sure if this change is a good idea this late. Users could have been
> > dependent on it being an unsigned value before. I believe this changes the
> > behavior of this code
> >
> > ```
> > int result = _mm_cvtness_sbh(X)
> > ```
> >
> > Previously it would have zero extended, but now it will sign extend.
> Yes, this should be a huge concern.
>
> Notice that intrinsic update has just documented these two intrinsics on
> 12/7/2021. So maybe we still have change to change it? And it's more theory
> right to do sign extension from a bfloat16 to int32.
I think this is the problem that we choose integer to represent BF16. Neither
zero extend nor sign extend makes sense to a floating type. But considering the
MSB of floating point is sign bit. Sign extend should be better in theory.
Maybe it's a good approach to use `__bf16`, but it is supported only by Clang.
We can't use it for intrinsics.
Anyway, I'm fine with keeping zero extend here. @craig.topper , do you think
it's acceptable to you if we just change `__bfloat16` to `short`?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D115611/new/
https://reviews.llvm.org/D115611
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