http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50223
Bug #: 50223
Summary: AVRGCC - dont clear r26 and r27.....its a (small)
waste of CPU cycles.
Classification: Unclassified
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: nickpar...@eaton.com
Host: PC Windows XP
Target: AVR Mega 128
Build: avr-gcc (WinAVR 20100110) 4.3.3
Dont clear r26 and r27.....its a (small) waste of CPU cycles.
Regards, Nick.
This function normalises a 32bit unsigned integer and returns
the number of shifts.
uint8_t ldgZeroCntNormU32(uint32_t * x)
{
uint8_t zCount=0;
uint8_t shft;
uint32_t quad;
quad=*x;
while (!(uint8_t)(quad >> 24))
{
zCount += 8;
quad <<=8;
}
shft = pgm_read_byte(&leadingZeros[(uint8_t)(quad >> 24)]);
*x = quad << shft;
return (zCount + shft);
}
.file "divu16u16.c"
2 __SREG__ = 0x3f
3 __SP_H__ = 0x3e
4 __SP_L__ = 0x3d
5 __CCP__ = 0x34
6 __tmp_reg__ = 0
7 __zero_reg__ = 1
15 .Ltext0:
16 .global ldgZeroCntNormU32
18 ldgZeroCntNormU32:
19 .LFB12:
20 .LM1:
21 .LVL0:
22 0000 CF93 push r28
23 0002 DF93 push r29
24 /* prologue: function */
25 /* frame size = 0 */
26 0004 EC01 movw r28,r24
27 .LM2:
28 0006 2881 ld r18,Y
29 0008 3981 ldd r19,Y+1
30 000a 4A81 ldd r20,Y+2
31 000c 5B81 ldd r21,Y+3
32 .LVL1:
33 .LM3:
34 000e 852F mov r24,r21
35 0010 9927 clr r25
36 0012 AA27 clr r26
37 0014 BB27 clr r27
38 .LVL2:
39 0016 E82F mov r30,r24
40 0018 8823 tst r24
41 001a 01F4 brne .L8
42 001c 60E0 ldi r22,lo8(0)
43 .LVL3:
44 .L4:
45 .LM4:
46 001e 685F subi r22,lo8(-(8))
47 .LM5:
48 0020 542F mov r21,r20
49 0022 432F mov r20,r19
50 0024 322F mov r19,r18
51 0026 2227 clr r18
52 .LM6:
53 0028 852F mov r24,r21
54 002a 9927 clr r25
55 002c AA27 clr r26
56 002e BB27 clr r27
57 0030 E82F mov r30,r24
58 0032 8823 tst r24
59 0034 01F0 breq .L4
60 .L3:
61 .LBB2:
62 .LM7:
63 0036 F0E0 ldi r31,lo8(0)
64 0038 E050 subi r30,lo8(-(leadingZeros))
65 003a F040 sbci r31,hi8(-(leadingZeros))
66 /* #APP */
67 ; 111 "divu16u16.c" 1
68 003c E491 lpm r30, Z
69
70 ; 0 "" 2
71 .LVL4:
72 /* #NOAPP */
73 .LBE2:
74 .LM8:
75 003e 0E2E mov r0,r30
76 0040 00C0 rjmp 2f
77 0042 220F 1: lsl r18
78 0044 331F rol r19
79 0046 441F rol r20
80 0048 551F rol r21
81 004a 0A94 2: dec r0
82 004c 02F4 brpl 1b
83 004e 2883 st Y,r18
84 0050 3983 std Y+1,r19
85 0052 4A83 std Y+2,r20
86 0054 5B83 std Y+3,r21
87 .LM9:
88 0056 8E2F mov r24,r30
89 0058 860F add r24,r22
90 /* epilogue start */
91 005a DF91 pop r29
92 005c CF91 pop r28
93 .LVL5:
94 005e 0895 ret
