Re: Please revert b2e843161d

> On 25 Jun 2026, at 17:42, Steve Kargl <[email protected]> wrote:
> 
> On 6/25/26 01:15, Andrew Turner wrote:
>>> On 24 Jun 2026, at 19:58, Steve Kargl <[email protected]> wrote:
>>> 
>>> Can someone with commit access please revert b2e843161dc3b?
>>> 
>>>   git log -r b2e843161dc3b79777e873183447c92ed9c3703a
>>>   Author: Andrew Turner <[email protected]>
>>>   Date:   Tue Nov 2 11:31:17 2021 +0000
>>> 
>>>   Use a builtin where possible in msun
>>> 
>>> 
>>> If one has a libm built with, e.g., -DUSE_BUILTIN_FMAF,
>>> and then tries to debug code that uses fmaf() where the
>>> compiler options include -fno-builtin, a segfault
>>> occurs.  I suggest purging all of the recent additions
>>> of USE_BUILTIN_*.  These are simply not needed as a compiler
>>> will use a builtin (if available) instead of a function from
>>> libm.
>> What architecture and compiler are you using to build libm?
>> I only enabled it on arm64 as both llvm and gcc will generate the optimal assembly instruction. Other architectures and compilers the builtin may generate a call to fmaf creating an infinite loop.
> 
> I'm using
> 
> % uname -a
> FreeBSD hotrats 16.0-CURRENT FreeBSD 16.0-CURRENT #0 main-n284956-de9fe28ab847: Fri Apr 10 10:15:09 PDT 2026 kargl@hotrats:/usr/obj/usr/src/amd64.amd64/sys/GENERIC amd64

I don’t expect it to work on amd64 in the general case. Godbolt shows both GCC and Clang generating an infinite loop jumping to its self [1]. It may work on some architecture levels, however I don’t know enough about amd64 to know if it’s safe to enable.

The USE_BUILTIN_* flags aren’t intended on being set by users as you found.

Andrew

[1] https://godbolt.org/z/c5W5hq35d