https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61772
Bug ID: 61772
Summary: RTL if-conversion removes asm volatile goto
Product: gcc
Version: 4.8.4
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: matz at gcc dot gnu.org
This is reduced from a bug our kernel people hit. The problem is
the use of asm volatile gotos inside a conditional, when the outgoing
blocks of the asm-goto are itself both empty. Ala:
------------------------- snip ---------------------------------------
/* { dg-do compile } */
/* { dg-final { scan-assembler-times "XXX" 2 } } */
static inline __attribute__((always_inline)) int dec_and_test (int *i)
{
asm volatile goto ("XXX %0, %l[cc_label]"
: : "m" (*i) : "memory" : cc_label);
return 0;
cc_label:
return 1;
}
extern int getit (int *);
int f (int *i, int cond)
{
if (cond) {
getit (0);
if (dec_and_test (i))
getit (i);
return 42;
}
if (dec_and_test (i))
(void)1;
return getit (i);
}
------------------ snap ----------------------------------------------
This should have two "XXX" in the resulting assembler, but will have only
one with any optimization level. It's the RTL if conversion that removes
the seemingly empty second dec_and_test(), because the then-block is
empty and because it doesn't check that the removed jump really is only
a jump without side effects.
I don't know if it's a regression (it probably isn't as I don't see that
ifcvt.c
was touched with the introduction of asm gotos), but it at least affects
trunk and 4.8.
