https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104882
Bug ID: 104882
Summary: [12 Regression] MVE: Wrong code at -O2 since
r12-1434-g046a3beb1673bf4a61c131373b6a5e84158e92bf
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: acoplan at gcc dot gnu.org
Target Milestone: ---
Created attachment 52608
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52608&action=edit
broken assembly output
The following code:
int i;
char src[1072];
char dst[72];
int main() {
for (i = 0; i < 128; i++)
src[i] = i;
__builtin_memcpy(dst, src, 7);
for (i = 0; i < 7; i++)
if (dst[i] != i)
__builtin_abort();
}
is miscompiled at -O2 since vectorization was enabled at -O2. With -O2
-ftree-vectorize, it is miscompiled earlier, starting with:
commit 046a3beb1673bf4a61c131373b6a5e84158e92bf
Author: Christophe Lyon <christophe.l...@linaro.org>
Date: Thu Jun 3 15:35:50 2021
arm: Auto-vectorization for MVE: add pack/unpack patterns
It looks like we do some dubious packing of vector elements before storing to
src. If I change the last loop to print the elements of dst instead, I see:
0 8 4 12 1 9 5
it should of course print:
0 1 2 3 4 5 6.
The broken code is attached. The testcase above was reduced from
gcc/testsuite/gcc.c-torture/execute/memcpy-1.c.
