http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60722
Bug ID: 60722
Summary: __builtin_choose_expr() does not allow 'CONST_EXP'
using const variable
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: yann at droneaud dot fr
Created attachment 32498
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32498&action=edit
testcase
Hi,
I'm trying to use __builtin_choose_expr() with a test against a const variable:
#define VALUE 123
int
test(void)
{
const int value = VALUE;
int v1, v2;
v1 = __builtin_choose_expr(__builtin_constant_p(VALUE),
(__builtin_choose_expr(VALUE >= 10,
2,
(__builtin_choose_expr(VALUE >= 0,
1,
0)))),
-1);
v1 = __builtin_choose_expr(__builtin_constant_p(value),
(__builtin_choose_expr(value >= 10,
2,
(__builtin_choose_expr(value >= 0,
1,
0)))),
-1);
return v1 - v2;
}
The first expression is considering a constant defined as a macro.
And the second expression is considering a constant variable.
With gcc 4.9.0 20140313 (experimental), I'm facing the following error:
$ /opt/gcc/bin/gcc -O2 -c test.c
test.c: In function ‘test’:
test.c:21:11: erreur: first argument to ‘__builtin_choose_expr’ not a constant
(__builtin_choose_expr(value >= 0,
^
test.c:19:9: erreur: first argument to ‘__builtin_choose_expr’ not a constant
(__builtin_choose_expr(value >= 10,
^
(Note: with gcc 4.8, I'm also having the issue with _builtin_constant_p(value),
as bug #19449)
It's a pity gcc is not able to consider (value >= 0) as a constant expression
while its obvious
that 'value' is a constant variable (!).
It makes usage of __builtin_choose_expr() not applicable in my case.
