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

gcc/ChangeLog

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

gcc/common.md

@@ -80,14 +80,14 @@
 (define_constraint "E"
   "Matches a floating-point constant."
   (ior (match_test "CONST_DOUBLE_AS_FLOAT_P (op)")
-       (match_test "GET_CODE (op) == CONST_VECTOR
+       (match_test "CONSTANT_P (op)
 		    && GET_MODE_CLASS (GET_MODE (op)) == MODE_VECTOR_FLOAT")))
 
 ;; There is no longer a distinction between "E" and "F".
 (define_constraint "F"
   "Matches a floating-point constant."
   (ior (match_test "CONST_DOUBLE_AS_FLOAT_P (op)")
-       (match_test "GET_CODE (op) == CONST_VECTOR
+       (match_test "CONSTANT_P (op)
 		    && GET_MODE_CLASS (GET_MODE (op)) == MODE_VECTOR_FLOAT")))
 
 (define_constraint "X"

gcc/doc/rtl.texi

@@ -1667,14 +1667,17 @@ Usually that is the only mode for which a label is directly valid.
 
 @findex const
 @item (const:@var{m} @var{exp})
-Represents a constant that is the result of an assembly-time
-arithmetic computation.  The operand, @var{exp}, is an expression that
-contains only constants (@code{const_int}, @code{symbol_ref} and
-@code{label_ref} expressions) combined with @code{plus} and
-@code{minus}.  However, not all combinations are valid, since the
-assembler cannot do arbitrary arithmetic on relocatable symbols.
-
-@var{m} should be @code{Pmode}.
+Wraps an rtx computation @var{exp} whose inputs and result do not
+change during the execution of a thread.  There are two valid uses.
+The first is to represent a global or thread-local address calculation.
+In this case @var{exp} should contain @code{const_int},
+@code{symbol_ref}, @code{label_ref} or @code{unspec} expressions,
+combined with @code{plus} and @code{minus}.  Any such @code{unspec}s
+are target-specific and typically represent some form of relocation
+operator.  @var{m} should be a valid address mode.
+
+The second use of @code{const} is to wrap a vector operation.
+In this case @var{exp} must be a @code{vec_duplicate} expression.
 
 @findex high
 @item (high:@var{m} @var{exp})

gcc/emit-rtl.c

@@ -1470,7 +1470,7 @@ gen_lowpart_common (machine_mode mode, rtx x)
 	return gen_rtx_fmt_e (GET_CODE (x), int_mode, XEXP (x, 0));
     }
   else if (GET_CODE (x) == SUBREG || REG_P (x)
-	   || GET_CODE (x) == CONCAT || GET_CODE (x) == CONST_VECTOR
+	   || GET_CODE (x) == CONCAT || const_vec_p (x)
 	   || CONST_DOUBLE_AS_FLOAT_P (x) || CONST_SCALAR_INT_P (x))
     return lowpart_subreg (mode, x, innermode);
 

gcc/expmed.c

@@ -5244,7 +5244,15 @@ make_tree (tree type, rtx x)
       return fold_convert (type, make_tree (t, XEXP (x, 0)));
 
     case CONST:
-      return make_tree (type, XEXP (x, 0));
+      {
+	rtx op = XEXP (x, 0);
+	if (GET_CODE (op) == VEC_DUPLICATE)
+	  {
+	    tree elt_tree = make_tree (TREE_TYPE (type), XEXP (op, 0));
+	    return build_vector_from_val (type, elt_tree);
+	  }
+	return make_tree (type, op);
+      }
 
     case SYMBOL_REF:
       t = SYMBOL_REF_DECL (x);

gcc/expr.c

@@ -9429,7 +9429,7 @@ expand_expr_real_2 (sepops ops, rtx target, machine_mode tmode,
       /* Careful here: if the target doesn't support integral vector modes,
 	 a constant selection vector could wind up smooshed into a normal
 	 integral constant.  */
-      if (CONSTANT_P (op2) && GET_CODE (op2) != CONST_VECTOR)
+      if (CONSTANT_P (op2) && !VECTOR_MODE_P (GET_MODE (op2)))
 	{
 	  tree sel_type = TREE_TYPE (treeop2);
 	  machine_mode vmode

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;
 }