[Bug rtl-optimization/45394] [4.6 regression] gnat fails to build on s390, trunk 20100918

[aoliva at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45394

--- Comment #10 from Alexandre Oliva <aoliva at gcc dot gnu.org> 2010-10-07 06:15:15 UTC ---
(In reply to comment #6)
> The combiner swaps 2 insns.

This swap looks correct to me.  Presumably reg 85 is being dropped, so moving
the debug_insn down to a point at which it can refer to the used value should
be fine, no?  Is this move even related with the bug?  Why?

I'm trying to figure out why this change that drops “after”, presumably needed
for this very kind of situation, is correct, but I can't easily get an
environment in which I can duplicate the problem.  A cross compiler (without
target libs) doesn't seem to be enough (or at least I don't know how to run it
to trigger the problem).  Help?