Store VECTOR_CST_NELTS directly in tree_node

Previously VECTOR_CST_NELTS (t) read the number of elements from
TYPE_VECTOR_SUBPARTS (TREE_TYPE (t)).  There were two ways of handling
this with variable TYPE_VECTOR_SUBPARTS: either forcibly convert the
number to a constant (which is doable) or store the number directly
in the VECTOR_CST.  The latter seemed better, since it involves less
pointer chasing and since the tree_node u field is otherwise unused
for VECTOR_CST.  It would still be easy to switch to the former in
future if we need to free up the field for someting else.

The patch also changes various bits of VECTOR_CST code to use
VECTOR_CST_NELTS instead of TYPE_VECTOR_SUBPARTS when iterating
over VECTOR_CST_ELTs.  Also, when the two are checked for equality,
the patch prefers to read VECTOR_CST_NELTS (which must be constant)
and check against TYPE_VECTOR_SUBPARTS, instead of the other way
around.

2017-09-14  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree-core.h (tree_base::u): Add an "nelts" field.
	(tree_vector): Use VECTOR_CST_NELTS as the length.
	* tree.c (tree_size): Likewise.
	(make_vector): Initialize VECTOR_CST_NELTS.
	* tree.h (VECTOR_CST_NELTS): Use the u.nelts field.
	* cfgexpand.c (expand_debug_expr): Use VECTOR_CST_NELTS instead of
	TYPE_VECTOR_SUBPARTS.
	* expr.c (const_vector_mask_from_tree): Consistently use "units"
	as the number of units, setting it from VECTOR_CST_NELTS.
	(const_vector_from_tree): Likewise.
	* fold-const.c (negate_expr_p): Use VECTOR_CST_NELTS instead of
	TYPE_VECTOR_SUBPARTS for the number of elements in a VECTOR_CST.
	(fold_negate_expr_1): Likewise.
	(fold_convert_const): Likewise.
	(const_binop): Likewise.  Differentiate the number of output and
	input elements.
	(const_unop): Likewise.
	(fold_ternary_loc): Use VECTOR_CST_NELTS for the number of elements
	in a VECTOR_CST, asserting that it is the same as TYPE_VECTOR_SUBPARTS
	in cases that did the opposite.

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

From-SVN: r252758

1 files changed, 6 insertions, 8 deletions

diff --git a/gcc/expr.c b/gcc/expr.c
index 989badc..a9689a6 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -11700,18 +11700,17 @@ static rtx
 const_vector_mask_from_tree (tree exp)
 {
   rtvec v;
-  unsigned i;
-  int units;
+  unsigned i, units;
   tree elt;
   machine_mode inner, mode;
 
   mode = TYPE_MODE (TREE_TYPE (exp));
-  units = GET_MODE_NUNITS (mode);
+  units = VECTOR_CST_NELTS (exp);
   inner = GET_MODE_INNER (mode);
 
   v = rtvec_alloc (units);
 
-  for (i = 0; i < VECTOR_CST_NELTS (exp); ++i)
+  for (i = 0; i < units; ++i)
     {
       elt = VECTOR_CST_ELT (exp, i);
 
@@ -11756,8 +11755,7 @@ static rtx
 const_vector_from_tree (tree exp)
 {
   rtvec v;
-  unsigned i;
-  int units;
+  unsigned i, units;
   tree elt;
   machine_mode inner, mode;
 
@@ -11769,12 +11767,12 @@ const_vector_from_tree (tree exp)
   if (VECTOR_BOOLEAN_TYPE_P (TREE_TYPE (exp)))
     return const_vector_mask_from_tree (exp);
 
-  units = GET_MODE_NUNITS (mode);
+  units = VECTOR_CST_NELTS (exp);
   inner = GET_MODE_INNER (mode);
 
   v = rtvec_alloc (units);
 
-  for (i = 0; i < VECTOR_CST_NELTS (exp); ++i)
+  for (i = 0; i < units; ++i)
     {
       elt = VECTOR_CST_ELT (exp, i);