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Re: Honnor ix86_accumulate_outgoing_args again


> > Unfortunately there is 40% regression on mgrid with -flto (and also noticeable
> > regression without LTO).  First thing I noticed is that we stop omitting frame
> > pointer in the hottest function.  This is because we see:
> 
> Does it happen with both 32-bit and 64-bit?
No, 32bit only.
> 
> > (set (reg/f:SI 7 sp)
> >     (plus:SI (reg/f:SI 7 sp)
> >         (const_int -8 [0xfffffffffffffff8])))
> >
> > and we end up marking SP as as uneliminable in:
> >
> >           /* See if this is setting the replacement hard register for
> >              an elimination.
> >
> >              If DEST is the hard frame pointer, we do nothing because
> >              we assume that all assignments to the frame pointer are
> >              for non-local gotos and are being done at a time when
> >              they are valid and do not disturb anything else.  Some
> >              machines want to eliminate a fake argument pointer (or
> >              even a fake frame pointer) with either the real frame
> >              pointer or the stack pointer.  Assignments to the hard
> >              frame pointer must not prevent this elimination.  */
> >
> >           for (ep = reg_eliminate;
> >                ep < &reg_eliminate[NUM_ELIMINABLE_REGS];
> >                ep++)
> >             if (ep->to_rtx == SET_DEST (x)
> >                 && SET_DEST (x) != hard_frame_pointer_rtx
> >                 && (! (SUPPORTS_STACK_ALIGNMENT && stack_realign_fp
> >                        && REGNO (ep->to_rtx) == STACK_POINTER_REGNUM)
> >                     || GET_CODE (SET_SRC (x)) != PLUS
> >                     || XEXP (SET_SRC (x), 0) != SET_DEST (x)
> >                     || ! CONST_INT_P (XEXP (SET_SRC (x), 1))))
> >               setup_can_eliminate (ep, false);
> >
> > It is because of
> >
> >                 && (! (SUPPORTS_STACK_ALIGNMENT && stack_realign_fp
> >                        && REGNO (ep->to_rtx) == STACK_POINTER_REGNUM)
> >
> > I am somewhat confused why do we need to stop eliminating.  Function is not
> > marked as needing drap (and in that case stack_realign_fp would be true)
> > What is this conditional shooting for?
> 
> Why is stack_realign_fp true?
It is false, but htere is ! in the conditional.

Honza
> 
> 
> -- 
> H.J.


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