Hi, All Can LNO gatekeeper help review this fix?
This bug happens in -m32 on x8664 linux.
Attached is the test case and patch.
command line is
opencc -O3 unsigned_loop_end.c -INLINE:ne=foo:ne=init:ne=check
-OPT:unroll_times_max=1 -m32
The bug happens when vectorization is happend on following loop.
int a[100]
int start;
unsigned i, end;
for( i = start; i < end; i++) {
a[i] = a[i+1];
}
with -m64 unsigned comparison is transformed to signed comparison in
STD_Canonicalize_Upper_Bound.
with -m32 unsigned comparison is kept in LNO.
Simd_Finalize_Loops will update loop_end align to vecotrize factor (vect)
i <= start + (((end - start + 1) / vect) * vect) -1
suppose start is 0, end is 2, vect is 4, original serial loop is
for( i = 0; i < 2; i++)
after Simd_Finalize_Loops transformation, simd loop becomes
for(i = 0, i <= -1; i++),
This loop will itreate 0xffffffff times.
The fix is change loop end to following form when compraion is unsigned.
i < start + (((end - start + 1) / vect) * vect)
As discussed with Shuxin, we also doubt why SIMD loop's upper need aligned
with vecotrized factor. Can SIMD only update loop's step?
like for(i = start, i <= end-1; i+= vector_factor)?
Best Regards
Shi, Hui
simd.patch
Description: Binary data
unsigned_loop_end.c
Description: Binary data
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