Hi,
this code:
unsigned long f (unsigned char *P)
{
unsigned long C;
C = ((unsigned long)P[1] << 24)
| ((unsigned long)P[2] << 16)
| ((unsigned long)P[3] << 8)
| ((unsigned long)P[4] << 0);
return C;
}
compiles to this:
00000000 <f>:
0: f9 2f mov r31, r25
2: e8 2f mov r30, r24
4: 61 81 ldd r22, Z+1 ; 0x01
6: 77 27 eor r23, r23
8: 88 27 eor r24, r24
a: 99 27 eor r25, r25
c: 96 2f mov r25, r22
e: 88 27 eor r24, r24
10: 77 27 eor r23, r23
12: 66 27 eor r22, r22
14: 22 81 ldd r18, Z+2 ; 0x02
16: 33 27 eor r19, r19
18: 44 27 eor r20, r20
1a: 55 27 eor r21, r21
1c: 53 2f mov r21, r19
1e: 42 2f mov r20, r18
20: 33 27 eor r19, r19
22: 22 27 eor r18, r18
24: 62 2b or r22, r18
26: 73 2b or r23, r19
28: 84 2b or r24, r20
2a: 95 2b or r25, r21
2c: 24 81 ldd r18, Z+4 ; 0x04
2e: 33 27 eor r19, r19
30: 44 27 eor r20, r20
32: 55 27 eor r21, r21
34: 62 2b or r22, r18
36: 73 2b or r23, r19
38: 84 2b or r24, r20
3a: 95 2b or r25, r21
3c: 23 81 ldd r18, Z+3 ; 0x03
3e: 33 27 eor r19, r19
40: 44 27 eor r20, r20
42: 55 27 eor r21, r21
44: 54 2f mov r21, r20
46: 43 2f mov r20, r19
48: 32 2f mov r19, r18
4a: 22 27 eor r18, r18
4c: 62 2b or r22, r18
4e: 73 2b or r23, r19
50: 84 2b or r24, r20
52: 95 2b or r25, r21
54: 08 95 ret
using this cmd line:
avr-gcc -c -Os f.c
IMO, most of the or, eor and mov instructions are unnecessary.
--
Summary: missed-optimization transforming a byte array to
unsigned long
Product: gcc
Version: 4.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: berndtrog at yahoo dot com
GCC target triplet: avr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27663
