------- Comment #2 from sliao at google dot com 2010-01-07 13:28 -------
Using flags, -march=armv5te -mthumb -Os, GCC 4.5.0 (trunk) generates the
following code:
00000000 <test>:
0: b570 push {r4, r5, r6, lr}
2: b084 sub sp, #16
4: 1c05 adds r5, r0, #0
6: 4668 mov r0, sp
8: 1c0e adds r6, r1, #0
a: 466c mov r4, sp
c: f7ff fffe bl 0 <func>
10: 2d01 cmp r5, #1
12: d102 bne.n 1a <func+0x1a>
14: 9b00 ldr r3, [sp, #0]
16: 9c01 ldr r4, [sp, #4]
18: e00c b.n 34 <func+0x34>
1a: 68a2 ldr r2, [r4, #8]
1c: 68e3 ldr r3, [r4, #12]
1e: 2e02 cmp r6, #2
20: d102 bne.n 28 <func+0x28>
22: 1c1c adds r4, r3, #0
24: 1c13 adds r3, r2, #0
26: e005 b.n 34 <func+0x34>
28: 6820 ldr r0, [r4, #0]
2a: 6861 ldr r1, [r4, #4]
2c: 1c1c adds r4, r3, #0
2e: 1c13 adds r3, r2, #0
30: 1a1b subs r3, r3, r0
32: 418c sbcs r4, r1
34: b004 add sp, #16
36: 1c18 adds r0, r3, #0
38: 1c21 adds r1, r4, #0
3a: bd70 pop {r4, r5, r6, pc}
----------------------------------------------------
GCC 4.2.1 generates the following code:
00000000 <test>:
0: b530 push {r4, r5, lr}
2: b085 sub sp, #20
4: 1c04 adds r4, r0, #0
6: 4668 mov r0, sp
8: 1c0d adds r5, r1, #0
a: f7ff fffe bl 0 <func>
e: 2c01 cmp r4, #1
10: d102 bne.n 18 <func+0x18>
12: 9800 ldr r0, [sp, #0]
14: 9901 ldr r1, [sp, #4]
16: e007 b.n 28 <func+0x28>
18: 9802 ldr r0, [sp, #8]
1a: 9903 ldr r1, [sp, #12]
1c: 2d02 cmp r5, #2
1e: d003 beq.n 28 <func+0x28>
20: 9b00 ldr r3, [sp, #0]
22: 9c01 ldr r4, [sp, #4]
24: 1ac0 subs r0, r0, r3
26: 41a1 sbcs r1, r4
28: b005 add sp, #20
2a: bd30 pop {r4, r5, pc}
------------------------------------------------------
GCC 4.2.1's code size is still smaller than GCC 4.5.0, and GCC 4.5.0's
generated code is similar to GCC 4.4.
I think it's still an issue in the trunk now.
For completeness sake, the source code is:
struct node
{
long long a;
long long b;
};
void func (struct node *n);
long long test (int from, int to)
{
struct node n;
func(&n);
if (from == 1)
return n.a;
else
{
if (to == 2)
return n.b;
else
return n.b - n.a;
}
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42502
