[Bug target/37633] [4.4 Regression] wrong register use on sh64

["amylaar at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #10 from amylaar at gcc dot gnu dot org  2009-03-08 16:35 -------
(In reply to comment #3)
> I've checked the old RA.  It does not assigned partially clobbered hard
> register because it is done only when non partially clobbered hard regs were
> tried first.  Sh has a lot of such registers therefore the chance to generate
> wrong code is small.
> 
> I can simulate the same behaviour for IRA by increasing costs for partially
> clobbered hard registers.  Currently rs6000 and sh define
> HARD_REGNO_CALL_PART_CLOBBERED.  So even the problem is solved for sh in
> different way, the patch increasing cost would be useful for rs6000.
> 
> Still, as I wrote, the complete solution (the mentioned cost increase will be
> still necessary in any case) would be save and restore partially clobbered
> hard-registers in caller-saves.c.

To avoid pessimizing code where partially clobbered registers are used
to allocate pseudos which are not affected by the partial clobbers, the
register allocator will have to provide caller_save.c with more information.
It needs to know which registers are live across a call in excess of the part
that is saved.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37633