Re: [10/nn] Widening optab cleanup

[Jeff Law <law at redhat dot com>]

On 10/23/2017 05:23 AM, Richard Sandiford wrote:
> widening_optab_handler had the comment:
> 
>       /* ??? Why does find_widening_optab_handler_and_mode attempt to
>          widen things that can't be widened?  E.g. add_optab... */
>       if (op > LAST_CONV_OPTAB)
>         return CODE_FOR_nothing;
> 
> I think it comes from expand_binop using
> find_widening_optab_handler_and_mode for two things: to test whether
> a "normal" optab like add_optab is supported for a standard binary
> operation and to test whether a "convert" optab is supported for a
> widening operation like umul_widen_optab.  In the former case from_mode
> and to_mode must be the same, in the latter from_mode must be narrower
> than to_mode.
> 
> For the former case, find_widening_optab_handler_and_mode is only really
> testing the modes that are passed in.  permit_non_widening must be true
> here.
> 
> For the latter case, find_widening_optab_handler_and_mode should only
> really consider new from_modes that are wider than the original
> from_mode and narrower than the original to_mode.  Logically
> permit_non_widening should be false, since widening optabs aren't
> supposed to take operands that are the same width as the destination.
> We get away with permit_non_widening being true because no target
> would/should define a widening .md pattern with matching modes.
> 
> But really, it seems better for expand_binop to handle these two
> cases itself rather than pushing them down.  With that change,
> find_widening_optab_handler_and_mode is only ever called with
> permit_non_widening set to false and is only ever called with
> a "proper" convert optab.  We then no longer need widening_optab_handler,
> we can just use convert_optab_handler directly.
> 
> The patch also passes the instruction code down to expand_binop_directly.
> This should be more efficient and removes an extra call to
> find_widening_optab_handler_and_mode.
> 
> 
> 2017-10-23  Richard Sandiford  <richard.sandiford@linaro.org>
> 	    Alan Hayward  <alan.hayward@arm.com>
> 	    David Sherwood  <david.sherwood@arm.com>
> 
> gcc/
> 	* optabs-query.h (convert_optab_p): New function, split out from...
> 	(convert_optab_handler): ...here.
> 	(widening_optab_handler): Delete.
> 	(find_widening_optab_handler): Remove permit_non_widening parameter.
> 	(find_widening_optab_handler_and_mode): Likewise.  Provide an
> 	override that operates on mode class wrappers.
> 	* optabs-query.c (widening_optab_handler): Delete.
> 	(find_widening_optab_handler_and_mode): Remove permit_non_widening
> 	parameter.  Assert that the two modes are the same class and that
> 	the "from" mode is narrower than the "to" mode.  Use
> 	convert_optab_handler instead of widening_optab_handler.
> 	* expmed.c (expmed_mult_highpart_optab): Use convert_optab_handler
> 	instead of widening_optab_handler.
> 	* expr.c (expand_expr_real_2): Update calls to
> 	find_widening_optab_handler.
> 	* optabs.c (expand_widen_pattern_expr): Likewise.
> 	(expand_binop_directly): Take the insn_code as a parameter.
> 	(expand_binop): Only call find_widening_optab_handler for
> 	conversion optabs; use optab_handler otherwise.  Update calls
> 	to find_widening_optab_handler and expand_binop_directly.
> 	Use convert_optab_handler instead of widening_optab_handler.
> 	* tree-ssa-math-opts.c (convert_mult_to_widen): Update calls to
> 	find_widening_optab_handler and use scalar_mode rather than
> 	machine_mode.
> 	(convert_plusminus_to_widen): Likewise.
OK.
jeff