Re: [PATCH 4/5] Generalise invalid_mode_change_p

[Jeff Law <law@redhat.com>]

On 09/22/14 01:34, Richard Sandiford wrote:
> Jeff Law <law@redhat.com> writes:
>> On 09/18/14 04:25, Richard Sandiford wrote:
>>> This is the main patch for the bug.  We should treat a register as invalid
>>> for a mode change if simplify_subreg_regno cannot provide a new register
>>> number for the result.  We should treat a class as invalid for a mode change
>>> if all registers in the class are invalid.  This is an extension of the old
>>> CANNOT_CHANGE_MODE_CLASS-based check (simplify_subreg_regno checks C_C_C_M).
>>>
>>> I forgot to say that the patch is a prerequisite to removing aarch64's
>>> C_C_C_M.  There are other prerequisites too, but removing C_C_C_M without
>>> this patch caused regressions in the existing testsuite, which is why no
>>> new tests are needed.
>>>
>>>
>>> gcc/
>>> 	* hard-reg-set.h: Include hash-table.h.
>>> 	(target_hard_regs): Add a finalize method and a x_simplifiable_subregs
>>> 	field.
>>> 	* target-globals.c (target_globals::~target_globals): Handle
>>> 	hard_regs->finalize.
>>> 	* rtl.h (subreg_shape): New structure.
>>> 	(shape_of_subreg): New function.
>>> 	(simplifiable_subregs): Declare.
>>> 	* reginfo.c (simplifiable_subreg): New structure.
>>> 	(simplifiable_subregs_hasher): Likewise.
>>> 	(simplifiable_subregs): New function.
>>> 	(invalid_mode_changes): Delete.
>>> 	(alid_mode_changes, valid_mode_changes_obstack): New variables.
>>> 	(record_subregs_of_mode): Remove subregs_of_mode parameter.
>>> 	Record valid mode changes in valid_mode_changes.
>>> 	(find_subregs_of_mode): Remove subregs_of_mode parameter.
>>> 	Update calls to record_subregs_of_mode.
>>> 	(init_subregs_of_mode): Remove invalid_mode_changes and bitmap
>>> 	handling.  Initialize new variables.  Update call to
>>> 	find_subregs_of_mode.
>>> 	(invalid_mode_change_p): Check new variables instead of
>>> 	invalid_mode_changes.
>>> 	(finish_subregs_of_mode): Finalize new variables instead of
>>> 	invalid_mode_changes.
>>> 	(target_hard_regs::finalize): New function.
>>> 	* ira-costs.c (print_allocno_costs): Call invalid_mode_change_p
>>> 	even when CLASS_CANNOT_CHANGE_MODE is undefined.
>>>
>>> Index: gcc/rtl.h
>>> ===================================================================
>>> --- gcc/rtl.h	2014-09-15 11:55:40.459855161 +0100
>>> +++ gcc/rtl.h	2014-09-15 12:26:21.249077760 +0100
>>> +/* Return the shape of a SUBREG rtx.  */
>>> +
>>> +static inline subreg_shape
>>> +shape_of_subreg (const_rtx x)
>>> +{
>>> +  return subreg_shape (GET_MODE (SUBREG_REG (x)),
>>> +		       SUBREG_BYTE (x), GET_MODE (x));
>>> +}
>>> +
>> Is there some reason you don't have a constructor that accepts a
>> const_rtx?
>
> I was worried that by allowing implicit const_rtx->subreg_shape
> conversions, it would be less obvious that the rtx has to have
> code SUBREG.  I.e. a checked conversion would be hidden in the
> constructor rather than being explicit.
>
> If with David's new rtx hierarchy we end up with an rtx_subreg
> subclass then I agree we should have a constructor that takes
> one of those.
Makes sense.

I'm not sure if I was explicit, but the patch is fine, that was more a 
curiosity on my part than anything.

jeff