[12/nn] Add an is_narrower_int_mode helper function

[Richard Sandiford <richard.sandiford@linaro.org>]

This patch adds a function for testing whether an arbitrary mode X
is an integer mode that is narrower than integer mode Y.  This is
useful for code like expand_float and expand_fix that could in
principle handle vectors as well as scalars.


2017-10-23  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* machmode.h (is_narrower_int_mode): New function
	* optabs.c (expand_float, expand_fix): Use it.
	* dwarf2out.c (rotate_loc_descriptor): Likewise.

Index: gcc/machmode.h
===================================================================
--- gcc/machmode.h	2017-10-23 11:44:06.561720156 +0100
+++ gcc/machmode.h	2017-10-23 11:44:23.979432614 +0100
@@ -893,6 +893,17 @@ is_complex_float_mode (machine_mode mode
   return false;
 }
 
+/* Return true if MODE is a scalar integer mode with a precision
+   smaller than LIMIT's precision.  */
+
+inline bool
+is_narrower_int_mode (machine_mode mode, scalar_int_mode limit)
+{
+  scalar_int_mode int_mode;
+  return (is_a <scalar_int_mode> (mode, &int_mode)
+	  && GET_MODE_PRECISION (int_mode) < GET_MODE_PRECISION (limit));
+}
+
 namespace mode_iterator
 {
   /* Start mode iterator *ITER at the first mode in class MCLASS, if any.  */
Index: gcc/optabs.c
===================================================================
--- gcc/optabs.c	2017-10-23 11:44:07.732431531 +0100
+++ gcc/optabs.c	2017-10-23 11:44:23.980398548 +0100
@@ -4820,7 +4820,7 @@ expand_float (rtx to, rtx from, int unsi
       rtx value;
       convert_optab tab = unsignedp ? ufloat_optab : sfloat_optab;
 
-      if (GET_MODE_PRECISION (GET_MODE (from)) < GET_MODE_PRECISION (SImode))
+      if (is_narrower_int_mode (GET_MODE (from), SImode))
 	from = convert_to_mode (SImode, from, unsignedp);
 
       libfunc = convert_optab_libfunc (tab, GET_MODE (to), GET_MODE (from));
@@ -5002,7 +5002,7 @@ expand_fix (rtx to, rtx from, int unsign
      that the mode of TO is at least as wide as SImode, since those are the
      only library calls we know about.  */
 
-  if (GET_MODE_PRECISION (GET_MODE (to)) < GET_MODE_PRECISION (SImode))
+  if (is_narrower_int_mode (GET_MODE (to), SImode))
     {
       target = gen_reg_rtx (SImode);
 
Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c	2017-10-23 11:44:05.684652559 +0100
+++ gcc/dwarf2out.c	2017-10-23 11:44:23.979432614 +0100
@@ -14530,8 +14530,7 @@ rotate_loc_descriptor (rtx rtl, scalar_i
   dw_loc_descr_ref op0, op1, ret, mask[2] = { NULL, NULL };
   int i;
 
-  if (GET_MODE (rtlop1) != VOIDmode
-      && GET_MODE_BITSIZE (GET_MODE (rtlop1)) < GET_MODE_BITSIZE (mode))
+  if (is_narrower_int_mode (GET_MODE (rtlop1), mode))
     rtlop1 = gen_rtx_ZERO_EXTEND (mode, rtlop1);
   op0 = mem_loc_descriptor (XEXP (rtl, 0), mode, mem_mode,
 			    VAR_INIT_STATUS_INITIALIZED);