http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47239
Summary: (int)&func & 3 is always optimized to 0 on some
targets
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: kkoj...@gcc.gnu.org
Targets like arm, hppa and sh64 use the lower bits of the address
of functions for special purposes. Even on those targets,
----
extern void plabel32_function (void);
int
is_plabel32 (void)
{
return ((unsigned long) &plabel32_function & 3);
}
----
which was the test case of PR 35705, is wrongly compiled with -O2.
It seems that tree-bit-ccp optimization evaluates the expression
((unsigned long) &plabel32_function & 3) to zero always.
With -fno-tree-bit-ccp, the result looks OK. For example, arm-eabi
compiler outputs
mov r0, #0
bx lr
with -O2 and
ldr r0, .L2
and r0, r0, #3
bx lr
.L3:
.align 2
.L2:
.word plabel32_function
with -O2 -fno-tree-bit-ccp. I've got similar results for hppa and sh64
compilers.
