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Re: [PATCH, rs6000] Fix PR72827 (ada bootstrap failure)


On Tue, Sep 06, 2016 at 03:24:24PM -0600, Jeff Law wrote:
> On 08/31/2016 01:08 AM, Eric Botcazou wrote:
> >>DSE should really detect this is happening and not do the wrong thing.
> >>Maybe add an assert somewhere?  Much easier to debug, that way.
> >
> >That sounds fragile, functions are allowed to fiddle with the frame 
> >pointer in
> >the prologue or epilogue (but of course not in the body).  I think that 
> >DSE is
> >not the only RTL pass which makes this assumption of invariant frame 
> >pointer
> >in the body, it seems rather fundamental in the RTL middle-end.
> That's my recollection as well -- I recall many patches flying by 
> through the years that assumed the frame pointer was invariant -- but 
> they were mostly (all?) in things that ran before we add the 
> prologue/epilogue to the INSN chain.

We could simply check if the frame pointer (or stack pointer) is changed
while RTX_FRAME_RELATED_P is not set?  Can that ever happen on "proper"
code?


Segher


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