[Bug c/63880] GCC overoptimization on local arrays of size 1

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63880

--- Comment #4 from Richard Biener rguenth at gcc dot gnu.org ---
Indeed this is a case we don't handle as QOI special-case (we accept other
cases of strictly undefined code though).

In this case it is recommended to just do

arglist *p = malloc (sizeof (arglist) + sizeof (char *) * 1000);

and as Andrew said not wrap arglist inside another struct which appends a
member.

[Bug c/63880] GCC overoptimization on local arrays of size 1

[petzke at teltarif dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63880

--- Comment #1 from Kai Petzke petzke at teltarif dot de ---
Created attachment 33980
  -- https://gcc.gnu.org/bugzilla/attachment.cgi?id=33980action=edit
A file with small modifications from overoptimized.c, that compiles correctly.

[Bug c/63880] GCC overoptimization on local arrays of size 1

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63880

Andrew Pinski pinskia at gcc dot gnu.org changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution|--- |INVALID

--- Comment #2 from Andrew Pinski pinskia at gcc dot gnu.org ---
In general, C code may rely on the fact

Maybe but this is undefined code in C.

[Bug c/63880] GCC overoptimization on local arrays of size 1

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63880

--- Comment #3 from Andrew Pinski pinskia at gcc dot gnu.org ---
if you allocated an arglist via malloc (or alloca) and not have a struct which
contained arglist, it would be valid (well GCC would do the correct thing as we
define it as being valid).