[Bug c/96907] New: [docs] document builtins for fputc and putc

[Bug c/96907] New: [docs] document builtins for fputc and putc

[ndesaulniers at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96907

            Bug ID: 96907
           Summary: [docs] document builtins for fputc and putc
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ndesaulniers at google dot com
                CC: rv at rasmusvillemoes dot dk, segher at kernel dot crashing.org
  Target Milestone: ---

In https://reviews.llvm.org/D86508, I'm going through and working on improving
Clang's compatibility with GCC in terms of supported compiler __builtin_
functions.  I noticed that __has_builtin works with putc, __builtin_putc,
fputc, and __builtin_fputc in GCC.  I think putc and fputc could be added to
this page. https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html

[Bug c/96907] [docs] document builtins for fputc and putc

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96907

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
putc was added by g-b53b5aa509

fputc has been there since before 2003.

[Bug c/96907] [docs] document builtins for fputc and putc

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96907

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
They are not really "builtins", they are merely present to have default
attributes attached to them.

[Bug c/96907] [docs] document builtins for fputc and putc

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96907

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |segher at gcc dot gnu.org

--- Comment #3 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Many other "builtins" documented there are only ever implemented with
libcalls as well?

[Bug c/96907] [docs] document builtins for fputc and putc

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96907

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
For various builtins it isn't merely about default attached attributes, but
also about the compiler understanding what the function does in more detail and
perhaps performing some optimizations on them, transform one function call into
another one, or understand some aliasing etc. behavior of it.
I'm not really sure it is a good idea to document it all.

[Bug c/96907] [docs] document builtins for fputc and putc

[ndesaulniers at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96907

--- Comment #5 from Nick Desaulniers <ndesaulniers at google dot com> ---
No preferences either way.  I was just comparing differences between compilers
for __has_builtin and noticed GCC returns true for those two.  Is that ok?

[Bug c/96907] [docs] document builtins for fputc and putc

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96907

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |msebor at gcc dot gnu.org

--- Comment #6 from Martin Sebor <msebor at gcc dot gnu.org> ---
Rather than en enumerating all the functions that are handled as built-ins (and
keeping them in sync with the code) it would be simpler to state that any
function prescribed by this or that revision of a standard may be implemented
as a built-in, and suggesting to use the __has_builtin() preprocessor function
to query support for each.

Besides adding attributes to their declarations, GCC transforms calls to some
of them into others (e.g., fputs to fputc, or fprintf to fputs or fputc) or
eliminated altogether (e.g., fputs("", f)).  It might be helpful to mention
that in the manual and point users who want to avoid such transformations to
-fno-builtin-<name>.