This CL fixes a bug in the code generation for I32AtomicCompareExchange
in Liftoff on ia32. The problem is the inconsistency that
LiftoffAssembler::PeekToRegister(...) introduces to the cache state.
PeekToRegister loads the value from the value stack into a register, but
does not pop the value off the stack. When the value was already stored
in a register, the use counter of that register gets decreased, even
though the value is still on the stack.
The problem arises when this register later gets reused, which is
necessary unfortunately on ia32. When SpillRegister is called for this
register, all stack values that are stored in this register get written
to memory. SpillRegister uses the use counter of the register to detect
when the register was spilled to all stack slots that were cached by
this register. However, as described above, the value stack and the use
counter are inconsistent at that moment, so SpillRegister finishes
early and does not spill the register to all stack values, and this
causes the bug later.
With this CL the decrement of the use counter gets delayed until when
the value actually gets popped off the stack.
R=clemensb@chromium.org
Bug: chromium:1145135
Change-Id: I07cb256a7e5135dbce41b246c120650635ad2758
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2602464
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72018}
