From: Joseph Myers <joseph@codesourcery.com>
To: Iain Sandoe <iain@sandoe.co.uk>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>,
"<ro@cebitec.uni-bielefeld.de>" <ro@CeBiTec.Uni-Bielefeld.DE>
Subject: Re: [PATCH] Darwin, crts: Provide scalb and significand as a crt [PR107631]
Date: Tue, 3 Jan 2023 18:15:19 +0000 [thread overview]
Message-ID: <44a1c1e5-c1b0-604c-aca5-bc42d93ee5ba@codesourcery.com> (raw)
In-Reply-To: <22D76CA0-7716-4646-9216-2D507AD1F7B2@sandoe.co.uk>
[-- Attachment #1: Type: text/plain, Size: 1497 bytes --]
On Sat, 31 Dec 2022, Iain Sandoe wrote:
> builtins.def unconditionally defines these builtins to be DEF_EXT_LIB_BUILTIN
> which expands to the libcall, this is currently hard-wired to FALLBACK_P = true.
>
> but, AFAIU the builtins.def descriptions:
>
> FALLBACK_P should be false if the libc (or libm, I suppose, if that’s different)
> does not have the function, perhaps that’s an underlying bug or at least an
> oversight?
>
> (or, of course, I misunderstood the intent of that param)
FALLBACK_P true means that it's the user's responsibility, if calling
__builtin_X, to make sure the library function X is also available in
cases where the call doesn't get expected inline - that is, that the API
for that __builtin_X function is that it may call an underlying library
function X, which is expected to exist and have a compatible interface.
Information about whether a function is present in libc / libm is
generally only relevant when __builtin_X might expand to call Y instead of
X; then GCC needs to know whether Y is available.
> - at present, it seems that this crt might be the least invasive
> solution (since ‘significand*()’ are not obsolete AFAIU, we still need
> to provide those implementations, regardless of any subsitution of
> scalbn*() in Modula-2).
The significand functions can be considered obsolete and were never in any
standard (thus glibc does not provide a version for _Float128, for
example).
--
Joseph S. Myers
joseph@codesourcery.com
next prev parent reply other threads:[~2023-01-03 18:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-30 10:20 Iain Sandoe
2022-12-30 22:26 ` Joseph Myers
2022-12-31 12:12 ` Iain Sandoe
2023-01-03 18:15 ` Joseph Myers [this message]
2023-01-03 20:07 ` Iain Sandoe
2023-01-03 21:34 ` Joseph Myers
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