------- Comment #9 from wilson at gcc dot gnu dot org 2006-02-10 02:03 -------
I've looked at the reload-branch also. I need two patches in order to
bootstrap it. One trivial obvious patch, and one hacked not technically
correct patch. It then bootstrapped and compiled this testcase correctly.
Since a major goal of the reload-branch is a complete rewrite of how
inheritance works, it isn't clear that the problem is fixed just because it
happened to work. So I took a look at the sources. The key detail here is
that reload-branch uses the scan_rtx function to determine what registers are
inputs and/or outputs of an instruction. The scan_rtx function does handle
{POST,PRE}_{INC,DEC} correctly, treating them the same as SET, so that the
operand gets marked as an output register. Although, looking at this, I can't
help but notice that {POST,PRE}_MODIFY do not get equivalent treatment. I
think this is a bug. Anyways, I'm convinced that reload-branch has a proper
solution to this bug, and I've got 3 bug reports against reload-branch that I
have to do something with now.
I remain convinced that my earlier suggestion for how to fix current reload is
correct. I just haven't gotten around to trying to write a patch yet. In
choose_reload_regs, where it calls regno_clobbered_p, we need an additional
check for registers modified by side-effects, as regno_clobbered_p does not
handle that itself. This could probably be as simple as checking for a REG_INC
note that mentions the equiv register.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25603
