------- Comment #3 from mingqiao dot wu at gmail dot com 2006-09-20 01:22
-------
(In reply to comment #2)
> You are violating C aliasing rules here (try -Wstrict-aliasing):
> return *(CTLFLOAT*)&bits;
Yes, -O2 turns on -fstrict-aliasing, and I saw many warnings like "warning:
dereferencing type-punned pointer will break strict-aliasing rules" without
specifying -Wstrict-aliasing explicitly because -Wall include it. I added
-Wstrict-aliasing to CFLAGS. The disassembly result is different but still not
correct. At 5e8 line, r3 is the latest value to return, but 574 line regard r2
is the return value. I noticed this warning did not appear in gcc-3.4.3. How
should I re-write such code to use -O2 correctly with gcc-4.1.1? Thanks.
00000560 <_CTL_Fixed2Float>:
560: e92d4010 stmdb sp!, {r4, lr}
564: e2504000 subs r4, r0, #0 ; 0x0
568: e24dd008 sub sp, sp, #8 ; 0x8
56c: 03a02000 moveq r2, #0 ; 0x0
570: 1a000002 bne 580 <_CTL_Fixed2Float+0x20>
574: e1a00002 mov r0, r2
578: e28dd008 add sp, sp, #8 ; 0x8
57c: e8bd8010 ldmia sp!, {r4, pc}
580: e0240fc4 eor r0, r4, r4, asr #31
584: e0400fc4 sub r0, r0, r4, asr #31
588: ebfffffe bl 0 <E3D_CLZ>
58c: e270200a rsbs r2, r0, #10 ; 0xa
590: 42623000 rsbmi r3, r2, #0 ; 0x0
594: 41a00314 movmi r0, r4, lsl r3
598: 51a00254 movpl r0, r4, asr r2
59c: e3500000 cmp r0, #0 ; 0x0
5a0: 03a035fe moveq r3, #1065353216 ; 0x3f800000
5a4: 058d3004 streq r3, [sp, #4]
5a8: 0a00000c beq 5e0 <_CTL_Fixed2Float+0x80>
5ac: e2823084 add r3, r2, #132 ; 0x84
5b0: e20330ff and r3, r3, #255 ; 0xff
5b4: e1a02b83 mov r2, r3, lsl #23
5b8: b2603000 rsblt r3, r0, #0 ; 0x0
5bc: a1a03100 movge r3, r0, lsl #2
5c0: b1a03103 movlt r3, r3, lsl #2
5c4: e58d2004 str r2, [sp, #4]
5c8: a3c304ff bicge r0, r3, #-16777216 ; 0xff000000
5cc: b3822102 orrlt r2, r2, #-2147483648 ; 0x80000000
5d0: b3c304ff biclt r0, r3, #-16777216 ; 0xff000000
5d4: a3c00502 bicge r0, r0, #8388608 ; 0x800000
5d8: b58d2004 strlt r2, [sp, #4]
5dc: b3c00502 biclt r0, r0, #8388608 ; 0x800000
5e0: e59d3004 ldr r3, [sp, #4]
5e4: e59d2004 ldr r2, [sp, #4]
5e8: e1833000 orr r3, r3, r0
5ec: e58d3004 str r3, [sp, #4]
5f0: eaffffdf b 574 <_CTL_Fixed2Float+0x14>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29140
