[rs6000] Use VIEW_CONVERT_EXPR to reinterpret vectors (PR 92515)

The new tree-cfg.c checking in r278245 tripped on folds of
ALTIVEC_BUILTIN_VPERM_*, which were using gimple_convert
rather than VIEW_CONVERT_EXPR to reinterpret the contents
of a vector as a different type.

2019-11-15  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR target/92515
	* config/rs6000/rs6000-call.c (rs6000_gimple_fold_builtin): Use
	VIEW_CONVERT_EXPR to reinterpret vectors as different types.

From-SVN: r278292

gcc/ChangeLog

+2019-11-15  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR target/92515
+	* config/rs6000/rs6000-call.c (rs6000_gimple_fold_builtin): Use
+	VIEW_CONVERT_EXPR to reinterpret vectors as different types.
+
 2019-11-15  Kwok Cheung Yeung  <kcy@codesourcery.com>
 
 	* config/gcn/gcn.c (gcn_regno_reg_class): Return VCC_CONDITIONAL_REG

gcc/config/rs6000/rs6000-call.c

@@ -6173,13 +6173,16 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
 	// convert arg0 and arg1 to match the type of the permute
 	// for the VEC_PERM_EXPR operation.
 	tree permute_type = (TREE_TYPE (permute));
-	tree arg0_ptype = gimple_convert (&stmts, loc, permute_type, arg0);
-	tree arg1_ptype = gimple_convert (&stmts, loc, permute_type, arg1);
+	tree arg0_ptype = gimple_build (&stmts, loc, VIEW_CONVERT_EXPR,
+					permute_type, arg0);
+	tree arg1_ptype = gimple_build (&stmts, loc, VIEW_CONVERT_EXPR,
+					permute_type, arg1);
 	tree lhs_ptype = gimple_build (&stmts, loc, VEC_PERM_EXPR,
 				      permute_type, arg0_ptype, arg1_ptype,
 				      permute);
 	// Convert the result back to the desired lhs type upon completion.
-	tree temp = gimple_convert (&stmts, loc, TREE_TYPE (lhs), lhs_ptype);
+	tree temp = gimple_build (&stmts, loc, VIEW_CONVERT_EXPR,
+				  TREE_TYPE (lhs), lhs_ptype);
 	gsi_insert_seq_before (gsi, stmts, GSI_SAME_STMT);
 	g = gimple_build_assign (lhs, temp);
 	gimple_set_location (g, loc);