On 2026-04-13 15:32, Bruno Haible via Gnulib discussion list wrote:
Whereas the abort()s in test-mcel.c look like a compiler bug: When I compile
with "-O2 -g" instead of "-O2", the abort occurs at a different line...
Looks like a compiler bug to me too. Harmen, do you know how to report
compiler bugs to Intel? Is that something you can do for us?
Here's how to reproduce the bug:
git clone https://git.savannah.gnu.org/git/gnulib.git
cd gnulib
./gnulib-tool --create-testdir --dir foo mcel
cd foo
./configure CC=icx
make check
This fails test-mcel-1.sh, test-mcel-2.sh, test-mcel-3.sh,
test-mcel-5.sh. You can more easily reproduce a failure by running this
command next:
cd gltests
./test-mcel 1
This outputs:
test-mcel.c:108: assertion 'sgn (mcel_tocmp (to_ascii, prev, c)) == cmp'
failed
before dumping core. The test failure occurs because the code generated
by idx is wrong. Source code that looks like this:
for (int ch = 0x80; ch < 0x200; ch++)
{
mcel_t c = mcel_ch (ch, 2);
ASSERT (c.ch == ch);
ASSERT (c.len == 2);
ASSERT (!c.err);
ASSERT (mcel_cmp (c, c) == 0);
ASSERT (mcel_eq (c, c));
ASSERT (mcel_tocmp (to_ascii, c, c) == 0);
ASSERT (mcel_cmp (prev, c) < 0);
ASSERT (mcel_cmp (c, prev) > 0);
ASSERT (! mcel_eq (prev, c));
ASSERT (! mcel_eq (c, prev));
ASSERT (mcel_tocmp (to_ascii, c, c) == 0);
int cmp = to_ascii (c.ch) ? -1 : 1;
ASSERT (sgn (mcel_tocmp (to_ascii, prev, c)) == cmp);
ASSERT (sgn (mcel_tocmp (to_ascii, c, prev)) == -cmp);
prev = c;
}
turns into the following assembly-language loop when compiled by icx
2025.3.3 (2025.3.3.20260319):
xorl %eax, %eax
.p2align 4
.LBB0_14: # =>This Inner Loop Header: Depth=1
leal (%rax,%rax), %ecx
leal 1(%rcx), %edx
andb $127, %dl
addb $2, %cl
andb $126, %cl
cmpb %cl, %dl
jae .LBB0_15
# %bb.63: # in Loop: Header=BB0_14 Depth=1
incl %eax
cmpl $191, %eax
jne .LBB0_14
where .LBB0_15 prints the assertion failure for the "sgn (mcel_tocmp
(to_ascii, prev, c)) == cmp" test. In other words, all the assertions
tests have been optimized away except for the "sgn (mcel_tocmp
(to_ascii, prev, c)) == cmp" test, and that test is optimized away half
the time but the half that isn't optimized away to nothing is optimized
into incorrect code.
In contrast GCC 15.2.1 20260123 (Red Hat 15.2.1-7) generates the
following code, which is slower but correct:
movl $127, %esi
jmp .L5
.p2align 4,,10
.p2align 3
.L8:
addl $2, %esi
movl $1, %eax
.L9:
andl $127, %edx
xorl %edi, %edi
movl %edx, %ecx
subl %eax, %ecx
testl %ecx, %ecx
setg %dil
shrl $31, %ecx
subl %ecx, %edi
cmpl $-1, %edi
jne .L73
subl %edx, %eax
xorl %edx, %edx
testl %eax, %eax
setg %dl
shrl $31, %eax
subl %eax, %edx
cmpl $1, %edx
jne .L74
cmpl $511, %esi
je .L75
.L5:
leal 1(%rsi), %edx
movl %edx, %eax
andl $127, %eax
je .L8
movl %esi, %ecx
movl %edx, %esi
movl %ecx, %edx
jmp .L9
.L75:
... where .L73 prints the failure for "sgn (mcel_tocmp (to_ascii, prev,
c)) == cmp", and .L74 prints the failure for "sgn (mcel_tocmp (to_ascii,
c, prev)) == -cmp".
