If __attribute__((optimize(...))) does not specify an optimisation
level (-Ox), we act as though the prevailing -Ox level had been restated.
So:
__attribute__((optimize("no-gcse")))
behaves like:
__attribute__((optimize("Ox", "no-gcse")))
where Ox is the current optimisation level. This means that if you
compile:
void bar (int);
void __attribute__((optimize("no-gcse"))) f1 (void)
{
bar (1);
bar (2);
}
void f2 (void)
{
bar (1);
bar (2);
}
with -O2 -fno-omit-frame-pointer, f1 will be implicitly use:
__attribute__((optimize("O2", "no-gcse")))
and this implicit -O2 will override the explicit -fno-omit-frame-pointer.
So f1 will be compiled without a frame pointer but f2 will be compiled
with one.
This behaviour isn't mentioned in the current documentation,
so this is either an implementation or a documentation bug.
In RichardG's opinion (and my opinion) it's an implementation
bug, so I'm marking it as "c".
--
Summary: Undocumented __attribute__((optimize)) behaviour when
the attribute specifies no optimisation level
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: rsandifo at gcc dot gnu dot org
GCC host triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38716
