$ cat simpleif.c
#include <stdio.h>
extern unsigned int debug_enabled_abc;
int main(int argc, char** argv) {
if (debug_enabled_abc)
printf("Hello World!\n");
return 0;
}
$ cat simple-debug.c
unsigned int debug_enabled_abc = 1;
$gcc -c simpleif.c -o simpleif.o -g -O3 -fPIC -fomit-frame-pointer
-march=nocona
$gcc -c simple-debug.c -o simple-debug.o -g -O3 -fPIC -fomit-frame-pointer
-march=nocona
$gcc simpleif.o simple-debug.o -o test -O3 -g -fPIC -fomit-frame-pointer
-march=nocona
$objdump -d test | grep '<main>' -A10
00000000004004e8 <main>:
4004e8: 48 83 ec 08 sub $0x8,%rsp
4004ec: 48 8b 05 8d 03 20 00 mov 0x20038d(%rip),%rax #
600880 <_DYNAMIC+0x1a8>
4004f3: 8b 00 mov (%rax),%eax
4004f5: 85 c0 test %eax,%eax
4004f7: 74 0c je 400505 <main+0x1d>
4004f9: 48 8d 3d f8 00 00 00 lea 0xf8(%rip),%rdi # 4005f8
<_IO_stdin_used+0x4>
400500: e8 0b ff ff ff callq 400410 <[EMAIL PROTECTED]>
400505: 31 c0 xor %eax,%eax
400507: 48 83 c4 08 add $0x8,%rsp
40050b: c3 retq
Notice the 4004ec loads an 8 byte value, when it is specified as int.
$ gcc -c simpleif.c -o simpleif.o -g -O3 -fomit-frame-pointer -march=nocona
$ gcc simpleif.o simple-debug.o -o test -O3 -g -fPIC -fomit-frame-pointer
-march=nocona
$ objdump -d test | grep '<main>' -A10
0000000000400498 <main>:
400498: 48 83 ec 08 sub $0x8,%rsp
40049c: 8b 05 e6 03 20 00 mov 0x2003e6(%rip),%eax #
600888 <debug_enabled_abc>
4004a2: 85 c0 test %eax,%eax
4004a4: 74 0a je 4004b0 <main+0x18>
4004a6: bf a8 05 40 00 mov $0x4005a8,%edi
4004ab: e8 10 ff ff ff callq 4003c0 <[EMAIL PROTECTED]>
4004b0: 31 c0 xor %eax,%eax
4004b2: 48 83 c4 08 add $0x8,%rsp
4004b6: c3 retq
4004b7: 90 nop
--
Summary: Sub optimal code generated in -fPIC mode
Product: gcc
Version: 4.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: davh at davh dot dk
GCC build triplet: x86_64-linux-gnu
GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34593
