| Summary: | optimization based on SSA "-O2 -fssa" uses wrong register | ||
|---|---|---|---|
| Product: | gcc | Reporter: | heinrich.brand |
| Component: | rtl-optimization | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED WONTFIX | ||
| Severity: | normal | CC: | gcc-bugs |
| Priority: | P3 | Keywords: | wrong-code |
| Version: | 3.3 | ||
| Target Milestone: | --- | ||
| Host: | sparc-sun-solaris2.8 | Target: | sparc-sun-solaris2.8 |
| Build: | sparc-sun-solaris2.8 | Known to work: | |
| Known to fail: | Last reconfirmed: | 2003-06-04 19:51:50 | |
|
Description
Andrew Pinski
2003-04-28 08:38:13 UTC
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.
Release:
Release: gcc version 3.3 20030407 (prerelease)
Environment:
SunOS 5.8 sparc
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" . Hello, I can confirm this problem on i686-linux. gcc 3.2.3 is fine, but both 3.3 branch and mainline (20030527) fail... I agree with Andrew that -fssa is probably going away in its current form, but still, this is broken, so I think we should probably just make this a low-priority bug, at least until - fssa finally is removed. Or should this perhaps be mapped to the RESOLVED: WONTFIX category? Dara Confirmed (at least for now)... -fssa is being removed from the mainline <http://gcc.gnu.org/ml/gcc/2003-07/ msg00070.html> so we will not fix this. The workaround is not to use -fssa at all. |