poly_int: vectorizable_conversion

This patch makes vectorizable_conversion cope with variable-length
vectors.  We already require the number of elements in one vector
to be a multiple of the number of elements in the other vector,
so the patch uses that to choose between widening and narrowing.

2018-01-03  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree-vect-stmts.c (vectorizable_conversion): Treat the number
	of units as polynomial.  Choose between WIDE and NARROW based
	on multiple_p.

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

From-SVN: r256139

gcc/ChangeLog

@@ -2,6 +2,14 @@
 	    Alan Hayward  <alan.hayward@arm.com>
 	    David Sherwood  <david.sherwood@arm.com>
 
+	* tree-vect-stmts.c (vectorizable_conversion): Treat the number
+	of units as polynomial.  Choose between WIDE and NARROW based
+	on multiple_p.
+
+2018-01-03  Richard Sandiford  <richard.sandiford@linaro.org>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
 	* tree-vect-stmts.c (simd_clone_subparts): New function.
 	(vectorizable_simd_clone_call): Use it instead of TYPE_VECTOR_SUBPARTS.
 

gcc/tree-vect-stmts.c

@@ -4115,8 +4115,8 @@ vectorizable_conversion (gimple *stmt, gimple_stmt_iterator *gsi,
   int ndts = 2;
   gimple *new_stmt = NULL;
   stmt_vec_info prev_stmt_info;
-  int nunits_in;
-  int nunits_out;
+  poly_uint64 nunits_in;
+  poly_uint64 nunits_out;
   tree vectype_out, vectype_in;
   int ncopies, i, j;
   tree lhs_type, rhs_type;
@@ -4251,12 +4251,15 @@ vectorizable_conversion (gimple *stmt, gimple_stmt_iterator *gsi,
 
   nunits_in = TYPE_VECTOR_SUBPARTS (vectype_in);
   nunits_out = TYPE_VECTOR_SUBPARTS (vectype_out);
-  if (nunits_in < nunits_out)
-    modifier = NARROW;
-  else if (nunits_out == nunits_in)
+  if (known_eq (nunits_out, nunits_in))
     modifier = NONE;
+  else if (multiple_p (nunits_out, nunits_in))
+    modifier = NARROW;
   else
+    {
+      gcc_checking_assert (multiple_p (nunits_in, nunits_out));
       modifier = WIDEN;
+    }
 
   /* Multiple types in SLP are handled by creating the appropriate number of
      vectorized stmts for each SLP node.  Hence, NCOPIES is always 1 in