http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47979
Summary: Problem in comparing integers
Product: gcc
Version: 4.4.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: xiaofeng...@google.com
Hi,
Here is a short summary of the problem. In the upgrading of gcc from 3.3 to
4.4.3, my hash unit test failed. I did some investigation and wrote a simple
program, which is attached, to reproduce this problem.
I use command below to compile this program:
g++ -g -pipe -O9 -funroll-loops -ffast-math -DNDEBUG -march=pentiumpro -DLINUX
-fpic -DGEOTARGETING -D_NG_POSIX_THREAD -D_RWCONFIG_${RWDBGNUM}_$RWLIBVERSION
-DRW_MULTI_THREAD -DRW_NO_XMSG -DRW_POSIX_D10_THREADS -D_REENTRANT -Wall
-Werror -Wno-sign-compare -Wno-write-strings -Wno-strict-aliasing
-Wno-unused-result abs_error.cc
and the result shows me "hash<0" is false. If "-O9" is removed from the command
line, "hash<0" is true.
I disassembly the obj file by objdump (objdump -Sl a.out), and below is digest
of the optimized result:
...
80484f1: b8 49 5e 86 da mov $0xda865e49,%eax
80484f6: 89 e5 mov %esp,%ebp
80484f8: 83 e4 f0 and $0xfffffff0,%esp
80484fb: 53 push %ebx
80484fc: e8 4c 00 00 00 call 804854d <__i686.get_pc_thunk.bx>
8048501: 81 c3 f3 1a 00 00 add $0x1af3,%ebx
8048507: 83 ec 1c sub $0x1c,%esp
804850a: 89 44 24 08 mov %eax,0x8(%esp)
804850e: c7 04 24 01 00 00 00 movl $0x1,(%esp)
8048515: 8d 8b ec e6 ff ff lea -0x1914(%ebx),%ecx
804851b: 89 4c 24 04 mov %ecx,0x4(%esp)
804851f: e8 dc fe ff ff call 8048400 <__printf_chk@plt>
8048524: 8d 83 f7 e6 ff ff lea -0x1909(%ebx),%eax
804852a: ba 49 5e 86 da mov $0xda865e49,%edx
804852f: 89 54 24 08 mov %edx,0x8(%esp)
8048533: 89 44 24 04 mov %eax,0x4(%esp)
8048537: c7 04 24 01 00 00 00 movl $0x1,(%esp)
804853e: e8 bd fe ff ff call 8048400 <__printf_chk@plt>
...
Seems "hash" and "result" both assigned 0xda865e49 (-628728247 in oct)
directly, for the optimizations.
I am not sure whether it is a problem in optimizations of the compiler, so I am
not sure whether it is correct for me to assign bug on this component. And,
because I am not familiar with i86 assembly, just read some tutorial to
understand a bit of the asm code, there must be some problems in the
investigations. Please let me know what do you think of this issue. Sure, if it
is my problem or there is a duplication of this bug, please let me know and
close the bug freely.
And, because it is almost impossible for our project to move back to gcc 3.3 or
try one more upgrade in short period, would you share me some way for us to
walk around this problem? (Sure, to make sure other code won't face this
problem any more)
Many thanks for your help!
