https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106884
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org
Keywords| |wrong-code
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2022-09-08
Depends on| |106811
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. r13-131-gc2a0d2e6f636c6 addressed some issues, but leaves others
such as shifts seen here. It's not clear if (int)1 << 33 is undefined behavior
in
GIMPLE, see PR106811. Note that ifcombine doesn't simply transform this to
(x & c) & (x & (1 << b)), thus removing the short-circuiting, instead it
computes tem = c | (1<<b) and checks (x & tem) == tem. That's probably safe
for arbitrary results of the undefined operation though.
One possibility might be to rewrite 1 << b to (1 << (b&31)) to make it always
defined, but that comes at an extra cost compared to how we treat signed
overflow.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106811
[Bug 106811] GENERIC and GIMPLE IL undefined behavior needs documenting
