Re: [PATCH 1/9] separate shrink-wrap: New command-line flag, status flag, hooks, and doc

[Jeff Law <law at redhat dot com>]

On 08/29/2016 03:31 AM, Bernd Schmidt wrote:
> On 08/01/2016 03:42 AM, Segher Boessenkool wrote:
> > +@deftypefn {Target Hook} void
> > TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS (sbitmap)
> > +Emit prologue insns for the components indicated by the parameter.
> > +@end deftypefn
> > +
> > +@deftypefn {Target Hook} void
> > TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS (sbitmap)
> > +Emit epilogue insns for the components indicated by the parameter.
> > +@end deftypefn
>
> How do these actually know where to save/restore registers? The frame
> pointer may have been eliminated, and SP isn't necessarily constant
> during the function. Seems like you'd have to calculate CFA reg/offset
> much like dwarf2out does and pass it to this hook.
So I think the confusion here is these hooks are independent of 
placement. ie, the target independent code does something like:

FOR_EACH_BB
  Build the component bitmap using the incoming edge components
  Emit the prologue components at the start of the block
  Emit the epilogue components at the end of the block


The components handled by a particular block start are set/cleared by 
the other hooks.

jeff