Allow vector CONSTs

This patch allows (const ...) wrappers to be used for rtx vector
constants, as an alternative to const_vector.  This is useful
for SVE, where the number of elements isn't known until runtime.

It could also be useful in future for fixed-length vectors, to
reduce the amount of memory needed to represent simple constants
with high element counts.  However, one nice thing about keeping
it restricted to variable-length vectors is that there is never
any need to handle combinations of (const ...) and CONST_VECTOR.

2017-11-01  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* doc/rtl.texi (const): Update description of address constants.
	Say that vector constants are allowed too.
	* common.md (E, F): Use CONSTANT_P instead of checking for
	CONST_VECTOR.
	* emit-rtl.c (gen_lowpart_common): Use const_vec_p instead of
	checking for CONST_VECTOR.
	* expmed.c (make_tree): Use build_vector_from_val for a CONST
	VEC_DUPLICATE.
	* expr.c (expand_expr_real_2): Check for vector modes instead
	of checking for CONST_VECTOR.
	* rtl.h (const_vec_p): New function.
	(const_vec_duplicate_p): Check for a CONST VEC_DUPLICATE.
	(unwrap_const_vec_duplicate): Handle them here too.

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

From-SVN: r254296

1 files changed, 21 insertions, 4 deletions

diff --git a/gcc/rtl.h b/gcc/rtl.h
index b01e306..373f8a2 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -2749,12 +2749,22 @@ extern rtx shallow_copy_rtx (const_rtx CXX_MEM_STAT_INFO);
 extern int rtx_equal_p (const_rtx, const_rtx);
 extern bool rtvec_all_equal_p (const_rtvec);
 
+/* Return true if X is some form of vector constant.  */
+
+inline bool
+const_vec_p (const_rtx x)
+{
+  return VECTOR_MODE_P (GET_MODE (x)) && CONSTANT_P (x);
+}
+
 /* Return true if X is a vector constant with a duplicated element value.  */
 
 inline bool
 const_vec_duplicate_p (const_rtx x)
 {
-  return GET_CODE (x) == CONST_VECTOR && rtvec_all_equal_p (XVEC (x, 0));
+  return ((GET_CODE (x) == CONST_VECTOR && rtvec_all_equal_p (XVEC (x, 0)))
+	  || (GET_CODE (x) == CONST
+	      && GET_CODE (XEXP (x, 0)) == VEC_DUPLICATE));
 }
 
 /* Return true if X is a vector constant with a duplicated element value.
@@ -2764,11 +2774,16 @@ template <typename T>
 inline bool
 const_vec_duplicate_p (T x, T *elt)
 {
-  if (const_vec_duplicate_p (x))
+  if (GET_CODE (x) == CONST_VECTOR && rtvec_all_equal_p (XVEC (x, 0)))
     {
       *elt = CONST_VECTOR_ELT (x, 0);
       return true;
     }
+  if (GET_CODE (x) == CONST && GET_CODE (XEXP (x, 0)) == VEC_DUPLICATE)
+    {
+      *elt = XEXP (XEXP (x, 0), 0);
+      return true;
+    }
   return false;
 }
 
@@ -2794,8 +2809,10 @@ template <typename T>
 inline T
 unwrap_const_vec_duplicate (T x)
 {
-  if (const_vec_duplicate_p (x))
-    x = CONST_VECTOR_ELT (x, 0);
+  if (GET_CODE (x) == CONST_VECTOR && rtvec_all_equal_p (XVEC (x, 0)))
+    return CONST_VECTOR_ELT (x, 0);
+  if (GET_CODE (x) == CONST && GET_CODE (XEXP (x, 0)) == VEC_DUPLICATE)
+    return XEXP (XEXP (x, 0), 0);
   return x;
 }