gccrs: Fix overflow intrinsic use before init

The overflow intrinsic returns a tuple of (value, boolean) where it value
is the operator result and boolean if it overflowed or not. The intrinsic
here did not initilize the resulting tuple and therefore was creating a use
before init error resulting in garbage results

Addresses Rust-GCC#1895

gcc/rust/ChangeLog:

	* backend/rust-compile-intrinsic.cc (op_with_overflow_inner): fix use before init

Signed-off-by: Philip Herron <[email protected]>

Author: philberty

gcc/rust/backend/rust-compile-intrinsic.cc

@@ -598,7 +598,25 @@ op_with_overflow_inner (Context *ctx, TyTy::FnType *fntype, tree_code op)
   if (!ctx->get_backend ()->function_set_parameters (fndecl, param_vars))
     return error_mark_node;
 
-  enter_intrinsic_block (ctx, fndecl);
+  rust_assert (fntype->get_num_substitutions () == 1);
+  auto &param_mapping = fntype->get_substs ().at (0);
+  const TyTy::ParamType *param_tyty = param_mapping.get_param_ty ();
+  TyTy::BaseType *resolved_tyty = param_tyty->resolve ();
+  tree template_parameter_type
+    = TyTyResolveCompile::compile (ctx, resolved_tyty);
+
+  // this should match y as well or we can take it from the TyTy structure
+  tree tmp_stmt = error_mark_node;
+  Bvariable *result_variable = ctx->get_backend ()->temporary_variable (
+    fndecl, NULL_TREE, template_parameter_type, NULL_TREE,
+    true /*address_is_taken*/, UNDEF_LOCATION, &tmp_stmt);
+  Bvariable *bool_variable
+    = ctx->get_backend ()->temporary_variable (fndecl, NULL_TREE,
+					       boolean_type_node, NULL_TREE,
+					       true /*address_is_taken*/,
+					       UNDEF_LOCATION, &tmp_stmt);
+
+  enter_intrinsic_block (ctx, fndecl, {result_variable, bool_variable});
 
   // BUILTIN op_with_overflow FN BODY BEGIN
   auto x = ctx->get_backend ()->var_expression (x_param, UNDEF_LOCATION);
@@ -628,24 +646,20 @@ op_with_overflow_inner (Context *ctx, TyTy::FnType *fntype, tree_code op)
     }
   rust_assert (overflow_builtin != error_mark_node);
 
-  // this should match y as well or we can take it from the TyTy structure
-  tree overflow_op_type = TREE_TYPE (x);
-  tree tmp_stmt = error_mark_node;
-  Bvariable *bvar
-    = ctx->get_backend ()->temporary_variable (fndecl, NULL_TREE,
-					       overflow_op_type, NULL_TREE,
-					       true /*address_is_taken*/,
-					       UNDEF_LOCATION, &tmp_stmt);
-  ctx->add_statement (tmp_stmt);
-
-  tree result_decl = bvar->get_tree (UNDEF_LOCATION);
+  tree bool_decl = bool_variable->get_tree (BUILTINS_LOCATION);
+  tree result_decl = result_variable->get_tree (BUILTINS_LOCATION);
   tree result_ref = build_fold_addr_expr_loc (BUILTINS_LOCATION, result_decl);
 
-  tree did_overflow_node
-    = build_call_expr_loc (BUILTINS_LOCATION, overflow_builtin, 3, x, y,
-			   result_ref);
+  tree builtin_call = build_call_expr_loc (BUILTINS_LOCATION, overflow_builtin,
+					   3, x, y, result_ref);
+
+  tree overflow_assignment
+    = ctx->get_backend ()->assignment_statement (bool_decl, builtin_call,
+						 BUILTINS_LOCATION);
+
+  ctx->add_statement (overflow_assignment);
 
-  std::vector<tree> vals = {result_decl, did_overflow_node};
+  std::vector<tree> vals = {result_decl, bool_decl};
   tree tuple_type = TREE_TYPE (DECL_RESULT (fndecl));
   tree result_expr
     = ctx->get_backend ()->constructor_expression (tuple_type, false, vals, -1,