rjmccall added inline comments.
================
Comment at: clang/lib/Basic/Targets/X86.cpp:381
HasBFloat16 = SSELevel >= SSE2;
----------------
pengfei wrote:
> I'm not sure if I understand the meaning of `HasFullBFloat16`. If it is used
> for target that supports arithmetic `__bf16`, we should not use `+fullbf16`
> but always enable it for SSE2, i.e., `HasFullBFloat16 = SSELevel >= SSE2`.
> Because X86 GCC already supports arithmetic for `__bf16`.
>
> If this is used in the way like `HasLegalHalfType`, we should enable it once
> we have a full BF16 ISA on X86. `fullbf16` doesn't make much sense to me.
At the moment, we haven't done the work to emulate BFloat16 arithmetic in any
of the three ways we can do that: Clang doesn't promote it in IRGen, LLVM
doesn't promote it in legalization, and we don't have compiler-rt functions for
it. If we emit these instructions, they'll just sail through LLVM and fail in
the backend. So in the short term, we have to restrict this to targets that
directly support BFloat16 arithmetic in hardware, which doesn't include x86.
Once we have that emulation support, I agree that the x86 targets should enable
this whenever they would enable `__bf16`.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D150913/new/
https://reviews.llvm.org/D150913
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