Widening optab cleanup

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.

2017-11-01  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.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r254302

1 files changed, 5 insertions, 29 deletions

diff --git a/gcc/optabs-query.c b/gcc/optabs-query.c
index 204ca60..440462b 100644
--- a/gcc/optabs-query.c
+++ b/gcc/optabs-query.c
@@ -401,44 +401,20 @@ can_vec_perm_p (machine_mode mode, bool variable, vec_perm_indices *sel)
   return true;
 }
 
-/* Like optab_handler, but for widening_operations that have a
-   TO_MODE and a FROM_MODE.  */
-
-enum insn_code
-widening_optab_handler (optab op, machine_mode to_mode,
-			machine_mode from_mode)
-{
-  unsigned scode = (op << 16) | to_mode;
-  if (to_mode != from_mode && from_mode != VOIDmode)
-    {
-      /* ??? 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;
-      scode |= from_mode << 8;
-    }
-  return raw_optab_handler (scode);
-}
-
 /* Find a widening optab even if it doesn't widen as much as we want.
    E.g. if from_mode is HImode, and to_mode is DImode, and there is no
-   direct HI->SI insn, then return SI->DI, if that exists.
-   If PERMIT_NON_WIDENING is non-zero then this can be used with
-   non-widening optabs also.  */
+   direct HI->SI insn, then return SI->DI, if that exists.  */
 
 enum insn_code
 find_widening_optab_handler_and_mode (optab op, machine_mode to_mode,
 				      machine_mode from_mode,
-				      int permit_non_widening,
 				      machine_mode *found_mode)
 {
-  for (; (permit_non_widening || from_mode != to_mode)
-	 && GET_MODE_SIZE (from_mode) <= GET_MODE_SIZE (to_mode)
-	 && from_mode != VOIDmode;
-       from_mode = GET_MODE_WIDER_MODE (from_mode).else_void ())
+  gcc_checking_assert (GET_MODE_CLASS (from_mode) == GET_MODE_CLASS (to_mode));
+  gcc_checking_assert (from_mode < to_mode);
+  FOR_EACH_MODE (from_mode, from_mode, to_mode)
     {
-      enum insn_code handler = widening_optab_handler (op, to_mode,
-						       from_mode);
+      enum insn_code handler = convert_optab_handler (op, to_mode, from_mode);
 
       if (handler != CODE_FOR_nothing)
 	{