https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110622
Bug ID: 110622
Summary: x86: Miscompilation at O1 level (O0 is working)
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: malat at debian dot org
Target Milestone: ---
I can trigger an assertion in highway unit test suite on Debian/i386 when using
-O1 (does not happen at -O0).
Symptoms:
[...]
f32x2: Log1p(5.5968112995194757e-20) expected 5.5968112995194757e-20 actual 0
ulp 5.28754e+08 max ulp 3
[...]
For some reason the code return exactly zero (0) during a math computation of a
log1p function. The code runs fine at O2 on all other Debian arches (amd64,
mipsel, armel, ppc32 ...).
Since the return value is exactly 0, I suspect this is not a case of excess
precision (x87). This is not a hardware issue as I can reproduce it on multiple
hosts (Debian buildds machine, and x86 porterbox).
If I extract the math logic and call it in a `main` function, then the compiler
is able to optimize the code correctly (even at O2) and return appropriate
result (correct tolerance).
I did not observe any suspicious behavior under valgrind and/or -fsanitize.
