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[Bug target/53383] Allow -mpreferred-stack-boundary=3 on x86-64
- From: "hubicka at ucw dot cz" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Sun, 20 May 2012 11:34:27 +0000
- Subject: [Bug target/53383] Allow -mpreferred-stack-boundary=3 on x86-64
- Auto-submitted: auto-generated
- References: <bug-53383-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
--- Comment #13 from Jan Hubicka <hubicka at ucw dot cz> 2012-05-20 11:34:27 UTC ---
> > This isn't necessary. If __int128 is put on stack by caller,
> > the stack must be aligned at 16 bytes.
>
> Not when you call function with -fpreferred-stack-boundary=3
> and it is itself compiled with -fpreferred-stack-boudnary=4
> and calls another functions passing __int128.
> Thus the ABI incompatibility.
... and the alignment code is there not to align stack frame, but to
align the __int128bit position within the argument area. The
va_arg calls beforehand are of unknon count.
> Honza