Fix type mismatch in SLPed constructors

[Richard Sandiford]

Having the "same" vector types with different modes means that we can
end up vectorising a constructor with a different mode from the lhs.
This patch adds a VIEW_CONVERT_EXPR in that case.

This showed up on existing tests when testing with fixed-length
-msve-vector-bits=128.

Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

Richard


2020-01-10  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-slp.c (vectorize_slp_instance_root_stmt): Use a
	VIEW_CONVERT_EXPR if the vectorized constructor has a diffeent
	type from the lhs.

Index: gcc/tree-vect-slp.c
===================================================================
--- gcc/tree-vect-slp.c	2020-01-06 17:59:49.126752227 +0000
+++ gcc/tree-vect-slp.c	2020-01-10 15:01:13.780190287 +0000
@@ -4306,6 +4306,10 @@ vectorize_slp_instance_root_stmt (slp_tr
 	{
 	  tree vect_lhs = gimple_get_lhs (child_stmt_info->stmt);
 	  tree root_lhs = gimple_get_lhs (instance->root_stmt->stmt);
+	  if (!useless_type_conversion_p (TREE_TYPE (root_lhs),
+					  TREE_TYPE (vect_lhs)))
+	    vect_lhs = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (root_lhs),
+			       vect_lhs);
 	  rstmt = gimple_build_assign (root_lhs, vect_lhs);
 	  break;
 	}