[PATCH 4/5] Generalise invalid_mode_change_p

Richard Sandiford richard.sandiford@arm.com
Mon Sep 22 07:34:00 GMT 2014


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.

Thanks,
Richard



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