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optimization/3384: PowerPC -funroll-loops -fbranch-count-reg misoptimization
- To: gcc-gnats at gcc dot gnu dot org
- Subject: optimization/3384: PowerPC -funroll-loops -fbranch-count-reg misoptimization
- From: Zoltan Hidvegi <hzoli at austin dot ibm dot com>
- Date: Fri, 22 Jun 2001 18:31:51 -0500
>Number: 3384
>Category: optimization
>Synopsis: PowerPC -funroll-loops -fbranch-count-reg misoptimization
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Fri Jun 22 16:36:01 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator: Zoltan Hidvegi
>Release: 3.0
>Organization:
>Environment:
System: AIX vlad 3 4 0005BA2F4C00
host: powerpc-ibm-aix4.3.3.0
build: powerpc-ibm-aix4.3.3.0
target: powerpc-ibm-aix4.3.3.0
configured with: ../gcc-3.0/configure --enable-languages=c,c++,java --enable-version-specific-runtime-libs --disable-nls
>Description:
gcc-3.0 miscompiles code with -O2 -funroll-loops
Workaround: use -fno-branch-count-reg or do not use -funroll-loops
This is a regression to 2.95.3 but only if you use -funroll-loops.
The testcase:
------------ BEGIN ---------------
typedef unsigned long ulong;
void
set_offsets(ulong *t, ulong idx, ulong n, ulong v)
{
ulong i;
for (i = idx; i < n; i += 2) {
t[i] = v;
}
}
int
main(void)
{
ulong a[8];
set_offsets(a, 0, 7, 0xdeafcabe);
return 1;
}
------------- END ----------------
>How-To-Repeat:
% gcc -O2 -funroll-loops -o bug bug.c
% ./bug
zsh: 16798 segmentation fault ./bug
>Fix:
Use -fno-branch-count-reg or do not use -funroll-loops
>Release-Note:
>Audit-Trail:
>Unformatted: