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* optimization/10519: optimization based on SSA "-O2 -fssa" uses wrong register
@ 2003-04-28 12:26 Heinrich.Brand
0 siblings, 0 replies; 2+ messages in thread
From: Heinrich.Brand @ 2003-04-28 12:26 UTC (permalink / raw)
To: gcc-gnats; +Cc: Erwin.Unruh
>Number: 10519
>Category: optimization
>Synopsis: optimization based on SSA "-O2 -fssa" uses wrong register
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Mon Apr 28 12:26:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator: Heinrich Brand
>Release: Release: gcc version 3.3 20030407 (prerelease)
>Organization:
>Environment:
SunOS 5.8 sparc
>Description:
The test below compiles and executes successfully
with -O2 but fails with -O2 -fssa. The disassembled code
differs in one register in one place. A function should add
2 input registers and return the sum but in the "-O2 -fssa" case
only one register is used in the add instruction.
(Source code is in How-To-Repeat.)
*******************************************************************
The dissembled code of both cases ("-O2" OK and "-O2 -fssa" wrong) :
*******************************************************************
-O2 :
fy()
0: 81 c3 e0 08 jmp %o7 + 8
4: 90 02 00 09 add %o0, %o1, %o0
*******************************************************************
-O2 -fssa :
fy()
0: 81 c3 e0 08 jmp %o7 + 8
-------------------- wrong register in add: ------------------------
4: 90 02 00 08 add %o0, %o0, %o0
*******************************************************************
both cases (only offsets differ):
main()
8: 9d e3 bf 90 save %sp, -112, %sp
c: 92 10 20 04 mov 4, %o1
10: 40 00 00 00 call 0x10
14: 90 10 20 03 mov 3, %o0
18: 80 a2 20 07 cmp %o0, 7
...
*******************************************************************
End of the disassembled code.
>How-To-Repeat:
The the test with output FAILED can be repeated by:
Compile following source code
with gcc 3.3 20030407 -O2 -fssa
and
execute resulting program
int printf(const char *format, ...);
int f(int a, int b){
int *xa,*xb;
xa=&a;xb=&b;
return *xa+*(xb);
}
int main(){
if( f(3,4)==7 )
printf("SUCCESSFUL\n");
else
printf("FAILED\n");
return 0;
}
>Fix:
Do not use "-O2 -fssa" .
>Release-Note:
>Audit-Trail:
>Unformatted:
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: optimization/10519: optimization based on SSA "-O2 -fssa" uses wrong register
@ 2003-04-28 12:46 Andrew Pinski
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Pinski @ 2003-04-28 12:46 UTC (permalink / raw)
To: nobody; +Cc: gcc-prs
The following reply was made to PR optimization/10519; it has been noted by GNATS.
From: Andrew Pinski <pinskia@physics.uc.edu>
To: Heinrich.Brand@fujitsu-siemens.com
Cc: gcc-gnats@gcc.gnu.org, Erwin.Unruh@fujitsu-siemens.com
Subject: Re: optimization/10519: optimization based on SSA "-O2 -fssa" uses wrong register
Date: Mon, 28 Apr 2003 08:38:13 -0400
-fssa is not ready for production use, from
<http://gcc.gnu.org/onlinedocs/gcc/Optimize-
Options.html#Optimize%20Options>:
Users should not specify this option, since it is not yet ready for
production use.
Since -fssa is going away in favor of something different, do not use
this flag.
Thanks,
Andrew Pinski
^ permalink raw reply [flat|nested] 2+ messages in thread
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2003-04-28 12:26 optimization/10519: optimization based on SSA "-O2 -fssa" uses wrong register Heinrich.Brand
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