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-O3 libgcc EH miscompilation: a first hint
- To: egcs-bugs at egcs dot cygnus dot com
- Subject: -O3 libgcc EH miscompilation: a first hint
- From: Franz Sirl <Franz dot Sirl-kernel at lauterbach dot com>
- Date: Thu, 1 Jul 1999 23:58:03 +0200
Hi,
it seems that -O3 currently optimizes the code produced by
__builtin_eh_return() away. The code in libgcc2.c/__throw() looks like:
handler = throw_helper (eh, pc, my_udata, &offset);
/* Now go! */
__builtin_eh_return ((void *)eh, offset, handler);
The working assembly with -O2 looks like:
f1c: 4b ff fb ed bl b08 <throw_helper>
f20: 81 3f 00 00 lwz r9,0(r31)
f24: 80 1e 80 44 lwz r0,-32700(r30)
f28: 80 9f 02 08 lwz r4,520(r31)
f2c: 7c 65 1b 78 mr r5,r3
f30: 90 09 00 04 stw r0,4(r9)
f34: 80 7f 02 0c lwz r3,524(r31)
f38: 48 00 00 10 b f48 <.L188+0xc>
00000f3c <.L188>:
f3c: 7c a9 03 a6 mtctr r5
f40: 7c 21 22 14 add r1,r1,r4
f44: 4e 80 04 20 bctr
f48: 81 61 00 00 lwz r11,0(r1)
f4c: 80 0b 00 04 lwz r0,4(r11)
f50: 81 8b ff 24 lwz r12,-220(r11)
f54: 7c 08 03 a6 mtlr r0
f58: 81 cb ff 28 lwz r14,-216(r11)
f5c: 81 eb ff 2c lwz r15,-212(r11)
f60: 82 0b ff 30 lwz r16,-208(r11)
and with -O3:
c44: 4b ff f7 d5 bl 418 <throw_helper>
c48: 81 21 00 00 lwz r9,0(r1)
c4c: 80 1e 80 20 lwz r0,-32736(r30)
c50: 80 81 02 08 lwz r4,520(r1)
c54: 7c 65 1b 78 mr r5,r3
c58: 90 09 00 04 stw r0,4(r9)
c5c: 80 61 02 0c lwz r3,524(r1)
00000c60 <.L348>:
c60: 80 01 03 04 lwz r0,772(r1)
c64: 81 81 02 24 lwz r12,548(r1)
c68: 7c 08 03 a6 mtlr r0
c6c: 81 c1 02 28 lwz r14,552(r1)
c70: 81 e1 02 2c lwz r15,556(r1)
c74: 82 01 02 30 lwz r16,560(r1)
the result of throw_helper is still moved to r5, but where did the mtctr/bctr
pair vanish to?
Franz.