Use rtx_mode_t instead of std::make_pair

This change makes the code less sensitive to the exact type of the mode,
i.e. it forces a conversion where necessary.  This becomes important
when wrappers like scalar_int_mode and scalar_mode can also be used
instead of machine_mode.

Using rtx_mode_t also abstracts away the representation.  The fact that
it's a std::pair rather than a custom class isn't important to users of
the interface.

gcc/
2016-11-18  Richard Sandiford  <richard.sandiford@arm.com>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

	* combine.c (try_combine): Use rtx_mode_t instead of std::make_pair.
	* dwarf2out.c (mem_loc_descriptor, loc_descriptor): Likewise.
	(add_const_value_attribute): Likewise.
	* explow.c (plus_constant): Likewise.
	* expmed.c (expand_mult, make_tree): Likewise.
	* expr.c (convert_modes): Likewise.
	* loop-doloop.c (doloop_optimize): Likewise.
	* postreload.c (reload_cse_simplify_set): Likewise.
	* simplify-rtx.c (simplify_const_unary_operation): Likewise.
	(simplify_binary_operation_1, simplify_const_binary_operation):
	(simplify_const_relational_operation, simplify_immed_subreg): Likewise.
	* wide-int.h: Update documentation to recommend rtx_mode_t
	instead of std::make_pair.

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

From-SVN: r242586

1 files changed, 1 insertions, 1 deletions

diff --git a/gcc/expr.c b/gcc/expr.c
index 985c2b3..a51c164 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -652,7 +652,7 @@ convert_modes (machine_mode mode, machine_mode oldmode, rtx x, int unsignedp)
 	 assume that all the bits are significant.  */
       if (GET_MODE_CLASS (oldmode) != MODE_INT)
 	oldmode = MAX_MODE_INT;
-      wide_int w = wide_int::from (std::make_pair (x, oldmode),
+      wide_int w = wide_int::from (rtx_mode_t (x, oldmode),
 				   GET_MODE_PRECISION (mode),
 				   unsignedp ? UNSIGNED : SIGNED);
       return immed_wide_int_const (w, mode);