https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80693
Alexandre Oliva <aoliva at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |aoliva at gcc dot
gnu.org
--- Comment #2 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
Created attachment 41371
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41371&action=edit
patch I'm testing to fix the bug
The problem is that combine creates a single insn with the AND and the compare,
still modifying the same REG that is also an AND operand. Later, it combines
that two-SETs insn with 2 other insns, an AND and a NOT, dropping the SET that
modified the REG but still referencing the earlier value of that REG. Then, it
attempts to combine the AND and the NOT, but since it still believes the REG
held the result of an AND with 1, that simplifies to a XOR with 1. The problem
is that the REG no longer holds the result of the AND, but combine failed to
detach the REG from the value of the dropped SET. This patch does just that.
