Re: [PATCH] Set stores_off_frame_dead_at_return to false if sibling call

[Jeff Law <law at redhat dot com>]

On 12/04/14 08:50, John David Anglin wrote:
> On 12/1/2014 11:57 AM, Jeff Law wrote:
> > Prior to reload (ie, in DSE1) there's a bit of magic in that we do
> > not set frame_read on call insns.  That may in fact be wrong and
> > possibly the source of the problem.
> >
> > /* This field is only used for the processing of const functions.
> > These functions cannot read memory, but they can read the stack
> > because that is where they may get their parms.  We need to be this
> > conservative because, like the store motion pass, we don't consider
> > CALL_INSN_FUNCTION_USAGE when processing call insns. Moreover, we
> > need to distinguish two cases: 1. Before reload (register
> > elimination), the stores related to outgoing arguments are stack
> > pointer based and thus deemed of non-constant base in this pass.
> > This requires special handling but also means that the frame
> > pointer based stores need not be killed upon encountering a const
> > function call.
> The above is wrong for sibcalls.  Sibcall arguments are relative to
> the incoming argument pointer.  Is this always the frame pointer?
I don't think it's always the frame pointer.  Don't we use an argument 
pointer for the PA64 runtime?  If I recall, it was the only port that 
had a non-eliminable argument pointer at the time.



> If that is the case, then it may be possible to eliminate stack based
>  stores when we have a sibcall before reload.
> > if (reload_completed || SIBLING_CALL_P (insn))
> > insn_info->frame_read = true;
> This works.
>
> Dave