[Bug middle-end/106725] LTO semantics for __attribute__((leaf))

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106725

--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 24 Aug 2022, dthorn at google dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106725
> 
> --- Comment #2 from Daniel Thornburgh <dthorn at google dot com> ---
> (In reply to Richard Biener from comment #1)
> > If GCC, with LTO, would partition the program into two LTRANS partitions,
> > one containing main and bar and one containing foo then applying this
> > optimization promise during LTRANS time on the main/bar partition would
> > be wrong as you say - but I think GCC doesn't do this.
> 
> In this case, foo() was already compiled to native code outside of LTO.
> Wouldn't this then mean that its contents wouldn't be available for the WPA and
> LTRANS phases of the LTO code generation? It seems like the compiler wouldn't
> know that foo() might call bar(), and the presence of `__attribute__((leaf))`
> would cause it to assume that it doesn't call bar().

As said, GCC shouldn't assume this since leaf is defined at translation
unit level, not at LTO level.