[66/77] Use scalar_mode for constant integers

This patch treats the mode associated with an integer constant as a
scalar_mode.  We can't use the more natural-sounding scalar_int_mode
because we also use (const_int 0) for bounds-checking modes.  (It might
be worth adding a bounds-specific code instead, but that's for another
day.)

This exposes a latent bug in simplify_immed_subreg, which for
vectors of CONST_WIDE_INTs would pass the vector mode rather than
the element mode to rtx_mode_t.

I think the:

		  /* We can get a 0 for an error mark.  */
		  || GET_MODE_CLASS (mode) == MODE_VECTOR_INT
		  || GET_MODE_CLASS (mode) == MODE_VECTOR_FLOAT

in immed_double_const is dead.  trunc_int_mode (via gen_int_mode)
would go on to ICE if the mode fitted in a HWI, and surely plenty
of other code would be confused to see a const_int be interpreted
as a vector.  We should instead be using CONST0_RTX (mode) if we
need a safe constant for a particular mode.

We didn't try to make these functions take scalar_mode arguments
because in many cases that would be too invasive at this stage.
Maybe it would become feasible in future.  Also, the long-term
direction should probably be to add modes to constant integers
rather than have then as VOIDmode odd-ones-out.  That would remove
the need for rtx_mode_t and thus remove the question whether they
should use scalar_int_mode, scalar_mode or machine_mode.

The patch also uses scalar_mode for the CONST_DOUBLE handling
in loc_descriptor.  In that case the mode can legitimately be
either floating-point or integral.

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* emit-rtl.c (immed_double_const): Use is_a <scalar_mode> instead
	of separate mode class checks.  Do not allow vector modes here.
	(immed_wide_int_const): Use as_a <scalar_mode>.
	* explow.c (trunc_int_for_mode): Likewise.
	* rtl.h (wi::int_traits<rtx_mode_t>::get_precision): Likewise.
	(wi::shwi): Likewise.
	(wi::min_value): Likewise.
	(wi::max_value): Likewise.
	* dwarf2out.c (loc_descriptor): Likewise.
	* simplify-rtx.c (simplify_immed_subreg): Fix rtx_mode_t argument
	for CONST_WIDE_INT.

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

From-SVN: r251517

1 files changed, 6 insertions, 13 deletions

diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index f0c09ff..15c25ec 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -599,7 +599,8 @@ rtx
 immed_wide_int_const (const wide_int_ref &v, machine_mode mode)
 {
   unsigned int len = v.get_len ();
-  unsigned int prec = GET_MODE_PRECISION (mode);
+  /* Not scalar_int_mode because we also allow pointer bound modes.  */
+  unsigned int prec = GET_MODE_PRECISION (as_a <scalar_mode> (mode));
 
   /* Allow truncation but not extension since we do not know if the
      number is signed or unsigned.  */
@@ -659,18 +660,10 @@ immed_double_const (HOST_WIDE_INT i0, HOST_WIDE_INT i1, machine_mode mode)
         (i.e., i1 consists only from copies of the sign bit, and sign
 	of i0 and i1 are the same), then we return a CONST_INT for i0.
      3) Otherwise, we create a CONST_DOUBLE for i0 and i1.  */
-  if (mode != VOIDmode)
-    {
-      gcc_assert (GET_MODE_CLASS (mode) == MODE_INT
-		  || GET_MODE_CLASS (mode) == MODE_PARTIAL_INT
-		  /* We can get a 0 for an error mark.  */
-		  || GET_MODE_CLASS (mode) == MODE_VECTOR_INT
-		  || GET_MODE_CLASS (mode) == MODE_VECTOR_FLOAT
-		  || GET_MODE_CLASS (mode) == MODE_POINTER_BOUNDS);
-
-      if (GET_MODE_BITSIZE (mode) <= HOST_BITS_PER_WIDE_INT)
-	return gen_int_mode (i0, mode);
-    }
+  scalar_mode smode;
+  if (is_a <scalar_mode> (mode, &smode)
+      && GET_MODE_BITSIZE (smode) <= HOST_BITS_PER_WIDE_INT)
+    return gen_int_mode (i0, mode);
 
   /* If this integer fits in one word, return a CONST_INT.  */
   if ((i1 == 0 && i0 >= 0) || (i1 == ~0 && i0 < 0))