[PATCH 4/9] regrename: Don't rename restores

[Jeff Law]

On 09/09/2016 02:59 PM, Segher Boessenkool wrote:
> On Thu, Sep 08, 2016 at 11:51:53AM -0600, Jeff Law wrote:
>> On 07/31/2016 07:42 PM, Segher Boessenkool wrote:
>>> A restore is supposed to restore some certain register.  Restoring it
>>> into some other register will not work.  Don't.
>>>
>>> 2016-06-07  Segher Boessenkool  <segher@kernel.crashing.org>
>>>
>>> 	* regrename.c (build_def_use): Invalidate chains that have a
>>> 	REG_CFA_RESTORE on some instruction.
>> Again, how is this different from a normal epilogue that restores
>> registers which regrename seems to not muck with.
>
> Good question.  Either way, it is always wrong to rename a register we
> restore from stack.
Agreed.  Somehow register renaming does the right thing for a normal 
epilogue.  I don't see anything in regrename that obviously treats the 
epilogue specially, there's check_new_reg_p, but I don't see that it 
inherently handles this case.

regrename seems to use the DF infrastructure, so I wouldn't be surprised 
if this is a symptom of incorrect DF information for the epilogues.  One 
way to potentially find out would be to tweak the DF code to mark all 
the callee saved regs as live at the return insns and see how that 
affects regrename's decision making.

jeff