[Bug rtl-optimization/24762] [killloop-branch] code motion of non-invariant expressions with hard registers.

["rakdver at atrey dot karlin dot mff dot cuni dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #8 from rakdver at atrey dot karlin dot mff dot cuni dot cz  2005-11-09 23:15 -------
Subject: Re:  [killloop-branch] code motion of non-invariant expressions with
hard registers.

> ------- Comment #6 from dberlin at gcc dot gnu dot org  2005-11-09 22:53 -------
> 1. Call clobbers aren't definitions. They are clobbers (IE kills).  They do not
> generate a new value, they simply specify the old value is dead.  Thus, you
> don't mean to say "df.c assumes call clobbers ...", because it's not an
> assumption.
> 
> 
> 2. The patch is actually an incorrect workaround.  The real problem is that
> df.c on mainline doesn't get reaching definitions right for a number of
> reasons.
> 
> For example, explicit clobbers in CALL_INSN_FUNCTION_USAGE but *not* in
> regs_invalidated_by_call will be treated as gen's, because they don't fall into
> the special case in df_bb_rd_local_compute.  But they are not gen's.
> 
> Have you tried making sure CLOBBER's don't get into the rd_gen set?
> 
> I imagine that will fix your bug.

I am fairly sure you are wrong, in this case.  The code is like

bb1:
call (throw);

bb2:

reg = r15

where r15 is set by exception handling.  The problem is that there
currently simply is no insn that defines r15.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24762