forwprop: Fix ICE when building a VEC_PERM_EXPR [PR94683]

The type compatibility handling in simplify_vector_constructor is
based on the number of elements and on element type compatibility,
but that's no longer enough to ensure that two vector types are
compatible.  This patch uses a VIEW_CONVERT_EXPR if the permutation
type and result type are distinct.

2020-04-21  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR tree-optimization/94683
	* tree-ssa-forwprop.c (simplify_vector_constructor): Use a
	VIEW_CONVERT_EXPR to handle mixtures of similarly-structured
	but distinct vector types.

gcc/testsuite/
	PR tree-optimization/94683
	* gcc.target/aarch64/sve/acle/general/pr94683.c: New test.

gcc/ChangeLog

+2020-04-21  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR tree-optimization/94683
+	* tree-ssa-forwprop.c (simplify_vector_constructor): Use a
+	VIEW_CONVERT_EXPR to handle mixtures of similarly-structured
+	but distinct vector types.
+
 2020-04-21  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/94641

gcc/testsuite/ChangeLog

+2020-04-21  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR tree-optimization/94683
+	* gcc.target/aarch64/sve/acle/general/pr94683.c: New test.
+
 2020-04-21  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/94383

gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr94683.c

+/* { dg-options "-O2 -msve-vector-bits=256" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+#include <arm_sve.h>
+
+typedef float v8sf __attribute__((vector_size(32)));
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+** test:
+**	fadd	z0\.s, p0/m, z0\.s, #1.0
+**	trn1	z0\.s, z0\.s, z0\.s
+**	fdiv	z0\.s, p0/m, z0\.s, z1\.s
+**	ret
+*/
+svfloat32_t
+test (svbool_t pg, svfloat32_t x, svfloat32_t y)
+{
+  v8sf a = svadd_x (pg, x, 1);
+  v8sf b = { a[0], a[0], a[2], a[2], a[4], a[4], a[6], a[6] };
+  return svdiv_x (pg, b, y);
+}
+
+#ifdef __cplusplus
+}
+#endif

gcc/tree-ssa-forwprop.c

@@ -2598,6 +2598,11 @@ simplify_vector_constructor (gimple_stmt_iterator *gsi)
 			    res, TYPE_SIZE (type), bitsize_zero_node);
       if (conv_code != ERROR_MARK)
 	res = gimple_build (&stmts, conv_code, type, res);
+      else if (!useless_type_conversion_p (type, TREE_TYPE (res)))
+	{
+	  gcc_assert (!targetm.compatible_vector_types_p (type, perm_type));
+	  res = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, res);
+	}
       /* Blend in the actual constant.  */
       if (converted_orig1)
 	res = gimple_build (&stmts, VEC_PERM_EXPR, type,