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Re: [PATCH 1/9] separate shrink-wrap: New command-line flag, status flag, hooks, and doc
On Mon, Aug 29, 2016 at 11:31:51AM +0200, 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.
There are many other reasons why separate shrink-wrapping can not be
done for a certain function, too; some target-specific.
The generic code (patch 8/9) does
+ /* We don't handle "strange" functions. */
+ if (cfun->calls_alloca
+ || cfun->calls_setjmp
+ || cfun->can_throw_non_call_exceptions
+ || crtl->calls_eh_return
+ || crtl->has_nonlocal_goto
+ || crtl->saves_all_registers)
+ return;
+
+ /* Ask the target what components there are. If it returns NULL, don't
+ do anything. */
+ sbitmap components = targetm.shrink_wrap.get_separate_components ();
and the rs6000 version of TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS
(path 9/9) then does
+ rs6000_stack_t *info = rs6000_stack_info ();
+
+ if (!(info->savres_strategy & SAVE_INLINE_GPRS)
+ || !(info->savres_strategy & REST_INLINE_GPRS)
+ || WORLD_SAVE_P (info))
+ return NULL;
and also checks for each component if it can access the save slot with
just one instruction. It can handle both the stack pointer (r1) and
the hard frame pointer (r31); it uses the same logic as the "ordinary"
prologue/epilogue would.
Segher