http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57356
Bug ID: 57356
Summary: gcc-4.8: SSE2 instructions generated with '-mno-sse2'
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: thutt at vmware dot com
The following example shows a defect in gcc 4.8 when using the
'-mno-sse2' command line option: SSE2 instructions are still
generated.
Compile with:
gcc-4.8 -m64 -O1 -mno-sse2 -c -o /tmp/gungla.o /tmp/gungla.c
Sample Code:
typedef struct s128 {
char x[16];
} s128;
typedef struct wrapper {
s128 elem;
} wrapper;
void test2(s128 *);
void
test(wrapper **p, int *num)
{
int i;
s128 *a = &(*p)->elem;
s128 b = *a;
for (i = 1; i < *num; i++) {
test2(a);
if (i == 10) {
*a = b;
break;
}
}
if (p) {
*p = 0;
}
}
We have not been able to simplify this code any further.
Disassembly of section .text:
0000000000000000 <test>:
0: 41 56 push %r14
2: 41 55 push %r13
4: 41 54 push %r12
6: 55 push %rbp
7: 53 push %rbx
8: 48 83 ec 10 sub $0x10,%rsp
c: 49 89 fe mov %rdi,%r14
f: 48 89 f5 mov %rsi,%rbp
12: 4c 8b 2f mov (%rdi),%r13
--> 15: f3 41 0f 6f 45 00 movdqu 0x0(%r13),%xmm0
--> 1b: 66 0f 7f 04 24 movdqa %xmm0,(%rsp)
20: 83 3e 01 cmpl $0x1,(%rsi)
23: 7f 32 jg 57 <test+0x57>
25: eb 22 jmp 49 <test+0x49>
27: 4c 89 e7 mov %r12,%rdi
2a: e8 00 00 00 00 callq 2f <test+0x2f>
2b: R_X86_64_PC32 test2-0x4
2f: 83 fb 0a cmp $0xa,%ebx
32: 75 0d jne 41 <test+0x41>
34: 66 0f 6f 0c 24 movdqa (%rsp),%xmm1
39: f3 41 0f 7f 4d 00 movdqu %xmm1,0x0(%r13)
3f: eb 08 jmp 49 <test+0x49>
41: 83 c3 01 add $0x1,%ebx
44: 39 5d 00 cmp %ebx,0x0(%rbp)
47: 7f de jg 27 <test+0x27>
49: 4d 85 f6 test %r14,%r14
4c: 74 1b je 69 <test+0x69>
4e: 49 c7 06 00 00 00 00 movq $0x0,(%r14)
55: eb 12 jmp 69 <test+0x69>
57: 4d 89 ec mov %r13,%r12
5a: 4c 89 ef mov %r13,%rdi
5d: e8 00 00 00 00 callq 62 <test+0x62>
5e: R_X86_64_PC32 test2-0x4
62: bb 01 00 00 00 mov $0x1,%ebx
67: eb d8 jmp 41 <test+0x41>
69: 48 83 c4 10 add $0x10,%rsp
6d: 5b pop %rbx
6e: 5d pop %rbp
6f: 41 5c pop %r12
71: 41 5d pop %r13
73: 41 5e pop %r14
75: c3 retq
One oddity is that using '-mno-sse', the offending instructions are
not generated. (Maybe this implies that the instructions are simply
misclassified as SSE, rather than SSE2?)
gcc-4.7 does not exhibit the problem with the same code.
Can you folks please confirm, or refute, if gcc-4.7 suffers from the
same defect?
Possibly related to bug 46716.
