https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88773
Bug ID: 88773
Summary: statement expression returning a cast treated as an
lvalue
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
As discussed in bug 88766 comment #4, GCC treats some statement expressions as
lvalues even though their last statement is an rvalue. As noted in the rest of
the discussion a statement expression should evaluate to an rvalue even if it's
last statement is an lvalue.
Besides adjusting GCC to reflect that the manual should be updated to explain
this.
$ cat u.c && gcc -O2 -S -Wall -Wextra -Wpedantic
-fdump-tree-optimized=/dev/stdout u.c
void f (void)
{
int i = 0;
++__extension__ ({ (int)i; }); // accepted (bug)
if (i != 1) // folded to false
__builtin_abort ();
}
int* g (void)
{
int i = 0;
int *p = &++__extension__ ({ (int)i; }); // rejected (good)
return p;
}
u.c: In function ‘g’:
u.c:12:12: error: lvalue required as unary ‘&’ operand
12 | int *p = &++__extension__ ({ (int)i; }); // rejected (good)
| ^
