http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53419
Bug #: 53419
Summary: loop incorrectly optimized to endless loop at -O2 for
table delimited by extern addresses (x86-32)
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: [email protected]
ReportedBy: [email protected]
Host: x86-32
Target: x86-32
The attached test case, duplicated below yields an infinite loop when compiled
by GCC 4.8 trunk version 187666. This appears to be a relatively recent
regression
(likely between 185454 and 186243).
typedef unsigned int size_t;
typedef void (*func_ptr_t) (void);
extern func_ptr_t init_array_begin[1];
extern func_ptr_t init_array_end[1];
void
per_thread_init (void)
{
size_t n_init = (init_array_end - init_array_begin);
int i;
for (i = 0; i < n_init; ++i)
{
func_ptr_t init_func = init_array_begin[i];
if (init_func)
(*init_func) ();
}
}
At -O1, the loop looks like this:
.L4:
movl init_array_begin(,%ebx,4), %eax
testl %eax, %eax
je .L3
call *%eax
.L3:
addl $1, %ebx
cmpl %esi, %ebx
jne .L4
At -O2 it looks like this.
.L5:
movl init_array_begin, %eax
testl %eax, %eax
je .L3
call *%eax
.L3:
cmpl $1, %ebx
jne .L5
The comparison "cmpl $1, %ebx" is problematic, as well as the lack of
indexing the array.
