c++: implement P1492 contracts

Implement the P1492 versions of contracts, along with extensions that
support the emulation of N4820 and other proposals. This implementation
assigns a concrete semantic (one of: ignore, assume, enforce, or
observe) to each contract attribute depending on its labels and
configuration options.

Co-authored-by: Andrew Sutton  <asutton@lock3software.com>
Co-authored-by: Andrew Marmaduke <amarmaduke@lock3software.com>
Co-authored-by: Michael Lopez <mlopez@lock3software.com>
Co-authored-by: Jason Merrill  <jason@redhat.com>

gcc/ChangeLog:

	* doc/invoke.texi: Document contracts flags.

gcc/c-family/ChangeLog:

	* c.opt: Add contracts flags.
	* c-cppbuiltin.cc (c_cpp_builtins): Add contracts feature-test
	macros.

gcc/cp/ChangeLog:

	* cp-tree.h (enum cp_tree_index): Add
	CPTI_PSEUDO_CONTRACT_VIOLATION.
	(pseudo_contract_violation_type): New macro.
	(struct saved_scope): Add x_processing_contract_condition.
	(processing_contract_condition): New macro.
	(comparing_override_contracts): New variable decl.
	(find_contract): New inline.
	(set_decl_contracts): New inline.
	(get_contract_semantic): New inline.
	(set_contract_semantic): New inline.
	* constexpr.cc (cxx_eval_assert): Split out from...
	(cxx_eval_internal_function): ...here.
	(cxx_eval_constant_expression): Use it for contracts.
	(potential_constant_expression_1): Handle contracts.
	* cp-gimplify.cc (cp_genericize_r): Handle contracts.
	* cp-objcp-common.cc (cp_tree_size): Handle contracts.
	(cp_common_init_ts): Handle contracts.
	(cp_handle_option): Handle contracts.
	* decl.cc (duplicate_decls): Handle contracts.
	(check_tag_decl): Check for bogus contracts.
	(start_decl): Check flag_contracts.
	(grokfndecl): Call rebuild_postconditions.
	(grokdeclarator): Handle contract attributes.
	(start_preparsed_function): Call start_function_contracts.
	(finish_function): Call finish_function_contracts.
	* decl2.cc (cp_check_const_attributes): Skip contracts.
	(comdat_linkage): Handle outlined contracts.
	* error.cc (dump_type): Handle null TYPE_IDENTIFIER.
	* g++spec.cc (EXPERIMENTAL): New macro.
	(lang_specific_driver): Add -lstdc++exp if -fcontracts.
	* mangle.cc (write_encoding): Handle outlined contracts.
	* module.cc (trees_out::fn_parms_init): Handle outlined contracts.
	(trees_in::fn_parms_init): Likewise.
	(check_mergeable_decl): Likewise.
	(module_state_config::get_dialect): Record -fcontracts.
	* parser.h (struct cp_unparsed_functions_entry): Add contracts.
	* parser.cc (unparsed_contracts): New macro.
	(push_unparsed_function_queues): Adjust.
	(contract_attribute_p): New.
	(cp_parser_statement): Check contracts.
	(cp_parser_decl_specifier_seq): Handle contracts.
	(cp_parser_skip_to_closing_square_bracket): Split out...
	(cp_parser_skip_up_to_closing_square_bracket): ...this fn.
	(cp_parser_class_specifier): Do contract late parsing.
	(cp_parser_class_head): Check contracts.
	(cp_parser_contract_role): New.
	(cp_parser_contract_mode_opt): New.
	(find_error, contains_error_p): New.
	(cp_parser_contract_attribute_spec): New.
	(cp_parser_late_contract_condition): New.
	(cp_parser_std_attribute_spec): Handle contracts.
	(cp_parser_save_default_args): Also save contracts.
	* pt.cc (register_parameter_specializations): No longer static.
	(register_local_identity): New.
	(check_explicit_specialization): Call remove_contract_attributes.
	(tsubst_contract, tsubst_contract_attribute): New.
	(tsubst_contract_attributes): New.
	(tsubst_attribute): Add comment.
	(tsubst_copy): Also allow parm when processing_contract_condition.
	(tsubst_expr): Handle contracts.
	(regenerate_decl_from_template): Handle contracts.
	* search.cc (check_final_overrider): Compare contracts.
	* semantics.cc (set_cleanup_locs): Skip POSTCONDITION_STMT.
	(finish_non_static_data_member): Check contracts.
	(finish_this_expr): Check contracts.
	(process_outer_var_ref): Handle contracts.
	(finish_id_expression_1): Handle contracts.
	(apply_deduced_return_type): Adjust contracts.
	* tree.cc (handle_contract_attribute): New.
	(get_innermost_component, is_this_expression): New.
	(comparing_this_references): New.
	(equivalent_member_references): New.
	(cp_tree_equal): Check it.
	* typeck.cc (check_return_expr): Apply contracts.
	* Make-lang.in: Add contracts.o.
	* config-lang.in: Add contracts.cc.
	* cp-tree.def (ASSERTION_STMT, PRECONDITION_STMT)
	(POSTCONDITION_STMT): New.
	* contracts.h: New file.
	* contracts.cc: New file.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/modules.exp: Pass dg-options to link command.
	* lib/g++.exp: Add -L for libstdc++exp.a.
	* g++.dg/contracts/backtrace_handler/assert_fail.cpp: New test.
	* g++.dg/contracts/backtrace_handler/handle_contract_violation.cpp: New test.
	* g++.dg/contracts/contracts-access1.C: New test.
	* g++.dg/contracts/contracts-assume1.C: New test.
	* g++.dg/contracts/contracts-assume2.C: New test.
	* g++.dg/contracts/contracts-assume3.C: New test.
	* g++.dg/contracts/contracts-assume4.C: New test.
	* g++.dg/contracts/contracts-assume5.C: New test.
	* g++.dg/contracts/contracts-assume6.C: New test.
	* g++.dg/contracts/contracts-comdat1.C: New test.
	* g++.dg/contracts/contracts-config1.C: New test.
	* g++.dg/contracts/contracts-constexpr1.C: New test.
	* g++.dg/contracts/contracts-constexpr2.C: New test.
	* g++.dg/contracts/contracts-constexpr3.C: New test.
	* g++.dg/contracts/contracts-conversion1.C: New test.
	* g++.dg/contracts/contracts-ctor-dtor1.C: New test.
	* g++.dg/contracts/contracts-ctor-dtor2.C: New test.
	* g++.dg/contracts/contracts-cv1.C: New test.
	* g++.dg/contracts/contracts-deduced1.C: New test.
	* g++.dg/contracts/contracts-deduced2.C: New test.
	* g++.dg/contracts/contracts-friend1.C: New test.
	* g++.dg/contracts/contracts-ft1.C: New test.
	* g++.dg/contracts/contracts-ignore1.C: New test.
	* g++.dg/contracts/contracts-ignore2.C: New test.
	* g++.dg/contracts/contracts-large-return.C: New test.
	* g++.dg/contracts/contracts-multiline1.C: New test.
	* g++.dg/contracts/contracts-multiple-inheritance1.C: New test.
	* g++.dg/contracts/contracts-multiple-inheritance2.C: New test.
	* g++.dg/contracts/contracts-nested-class1.C: New test.
	* g++.dg/contracts/contracts-nested-class2.C: New test.
	* g++.dg/contracts/contracts-nocopy1.C: New test.
	* g++.dg/contracts/contracts-override.C: New test.
	* g++.dg/contracts/contracts-post1.C: New test.
	* g++.dg/contracts/contracts-post2.C: New test.
	* g++.dg/contracts/contracts-post3.C: New test.
	* g++.dg/contracts/contracts-post4.C: New test.
	* g++.dg/contracts/contracts-post5.C: New test.
	* g++.dg/contracts/contracts-post6.C: New test.
	* g++.dg/contracts/contracts-pre1.C: New test.
	* g++.dg/contracts/contracts-pre10.C: New test.
	* g++.dg/contracts/contracts-pre2.C: New test.
	* g++.dg/contracts/contracts-pre2a1.C: New test.
	* g++.dg/contracts/contracts-pre2a2.C: New test.
	* g++.dg/contracts/contracts-pre3.C: New test.
	* g++.dg/contracts/contracts-pre4.C: New test.
	* g++.dg/contracts/contracts-pre5.C: New test.
	* g++.dg/contracts/contracts-pre6.C: New test.
	* g++.dg/contracts/contracts-pre7.C: New test.
	* g++.dg/contracts/contracts-pre9.C: New test.
	* g++.dg/contracts/contracts-redecl1.C: New test.
	* g++.dg/contracts/contracts-redecl2.C: New test.
	* g++.dg/contracts/contracts-redecl3.C: New test.
	* g++.dg/contracts/contracts-redecl4.C: New test.
	* g++.dg/contracts/contracts-redecl5.C: New test.
	* g++.dg/contracts/contracts-redecl6.C: New test.
	* g++.dg/contracts/contracts-redecl7.C: New test.
	* g++.dg/contracts/contracts-redecl8.C: New test.
	* g++.dg/contracts/contracts-tmpl-attr1.C: New test.
	* g++.dg/contracts/contracts-tmpl-spec1.C: New test.
	* g++.dg/contracts/contracts-tmpl-spec2.C: New test.
	* g++.dg/contracts/contracts-tmpl-spec3.C: New test.
	* g++.dg/contracts/contracts1.C: New test.
	* g++.dg/contracts/contracts10.C: New test.
	* g++.dg/contracts/contracts11.C: New test.
	* g++.dg/contracts/contracts12.C: New test.
	* g++.dg/contracts/contracts13.C: New test.
	* g++.dg/contracts/contracts14.C: New test.
	* g++.dg/contracts/contracts15.C: New test.
	* g++.dg/contracts/contracts16.C: New test.
	* g++.dg/contracts/contracts17.C: New test.
	* g++.dg/contracts/contracts18.C: New test.
	* g++.dg/contracts/contracts19.C: New test.
	* g++.dg/contracts/contracts2.C: New test.
	* g++.dg/contracts/contracts20.C: New test.
	* g++.dg/contracts/contracts22.C: New test.
	* g++.dg/contracts/contracts24.C: New test.
	* g++.dg/contracts/contracts25.C: New test.
	* g++.dg/contracts/contracts3.C: New test.
	* g++.dg/contracts/contracts35.C: New test.
	* g++.dg/contracts/contracts4.C: New test.
	* g++.dg/contracts/contracts5.C: New test.
	* g++.dg/contracts/contracts6.C: New test.
	* g++.dg/contracts/contracts7.C: New test.
	* g++.dg/contracts/contracts8.C: New test.
	* g++.dg/contracts/contracts9.C: New test.
	* g++.dg/modules/contracts-1_a.C: New test.
	* g++.dg/modules/contracts-1_b.C: New test.
	* g++.dg/modules/contracts-2_a.C: New test.
	* g++.dg/modules/contracts-2_b.C: New test.
	* g++.dg/modules/contracts-2_c.C: New test.
	* g++.dg/modules/contracts-3_a.C: New test.
	* g++.dg/modules/contracts-3_b.C: New test.
	* g++.dg/modules/contracts-4_a.C: New test.
	* g++.dg/modules/contracts-4_b.C: New test.
	* g++.dg/modules/contracts-4_c.C: New test.
	* g++.dg/modules/contracts-4_d.C: New test.
	* g++.dg/modules/contracts-tpl-friend-1_a.C: New test.
	* g++.dg/modules/contracts-tpl-friend-1_b.C: New test.
	* g++.dg/contracts/backtrace_handler/Makefile: New test.
	* g++.dg/contracts/backtrace_handler/README: New test.
	* g++.dg/contracts/backtrace_handler/example_out.txt: New test.
	* g++.dg/contracts/backtrace_handler/example_pretty.txt: New test.
	* g++.dg/contracts/backtrace_handler/prettytrace.sh: New test.
	* g++.dg/contracts/except_preload_handler/Makefile: New test.
	* g++.dg/contracts/except_preload_handler/README: New test.
	* g++.dg/contracts/except_preload_handler/assert_fail.cpp: New test.
	* g++.dg/contracts/except_preload_handler/handle_contract_violation.cpp: New test.
	* g++.dg/contracts/noexcept_preload_handler/Makefile: New test.
	* g++.dg/contracts/noexcept_preload_handler/README: New test.
	* g++.dg/contracts/noexcept_preload_handler/assert_fail.cpp: New test.
	* g++.dg/contracts/noexcept_preload_handler/handle_contract_violation.cpp: New test.
	* g++.dg/contracts/preload_handler/Makefile: New test.
	* g++.dg/contracts/preload_handler/README: New test.
	* g++.dg/contracts/preload_handler/assert_fail.cpp: New test.
	* g++.dg/contracts/preload_handler/handle_contract_violation.cpp: New test.
	* g++.dg/contracts/preload_nocontinue_handler/Makefile: New test.
	* g++.dg/contracts/preload_nocontinue_handler/README: New test.
	* g++.dg/contracts/preload_nocontinue_handler/assert_fail.cpp: New test.
	* g++.dg/contracts/preload_nocontinue_handler/handle_contract_violation.cpp: New test.
	* g++.dg/contracts/preload_nocontinue_handler/nocontinue.cpp: New test.

1 files changed, 67 insertions, 0 deletions

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index e352cf8..04a055d 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -46,6 +46,7 @@ static tree verify_stmt_tree_r (tree *, int *, void *);
 
 static tree handle_init_priority_attribute (tree *, tree, tree, int, bool *);
 static tree handle_abi_tag_attribute (tree *, tree, tree, int, bool *);
+static tree handle_contract_attribute (tree *, tree, tree, int, bool *);
 
 /* If REF is an lvalue, returns the kind of lvalue that REF is.
    Otherwise, returns clk_none.  */
@@ -3885,6 +3886,50 @@ called_fns_equal (tree t1, tree t2)
     return cp_tree_equal (t1, t2);
 }
 
+bool comparing_override_contracts;
+
+/* In a component reference, return the innermost object of
+   the postfix-expression.  */
+
+static tree
+get_innermost_component (tree t)
+{
+  gcc_assert (TREE_CODE (t) == COMPONENT_REF);
+  while (TREE_CODE (t) == COMPONENT_REF)
+    t = TREE_OPERAND (t, 0);
+  return t;
+}
+
+/* Returns true if T is a possibly converted 'this' or '*this' expression.  */
+
+static bool
+is_this_expression (tree t)
+{
+  t = get_innermost_component (t);
+  /* See through deferences and no-op conversions.  */
+  if (TREE_CODE (t) == INDIRECT_REF)
+    t = TREE_OPERAND (t, 0);
+  if (TREE_CODE (t) == NOP_EXPR)
+    t = TREE_OPERAND (t, 0);
+  return is_this_parameter (t);
+}
+
+static bool
+comparing_this_references (tree t1, tree t2)
+{
+  return is_this_expression (t1) && is_this_expression (t2);
+}
+
+static bool
+equivalent_member_references (tree t1, tree t2)
+{
+  if (!comparing_this_references (t1, t2))
+    return false;
+  t1 = TREE_OPERAND (t1, 1);
+  t2 = TREE_OPERAND (t2, 1);
+  return t1 == t2;
+}
+
 /* Return truthvalue of whether T1 is the same tree structure as T2.
    Return 1 if they are the same. Return 0 if they are different.  */
 
@@ -4219,6 +4264,13 @@ cp_tree_equal (tree t1, tree t2)
 	return false;
       return true;
 
+    case COMPONENT_REF:
+      /* If we're comparing contract conditions of overrides, member references
+	 compare equal if they designate the same member.  */
+      if (comparing_override_contracts)
+	return equivalent_member_references (t1, t2);
+      break;
+
     default:
       break;
     }
@@ -5062,6 +5114,10 @@ const struct attribute_spec std_attribute_table[] =
     handle_noreturn_attribute, attr_noreturn_exclusions },
   { "carries_dependency", 0, 0, true, false, false, false,
     handle_carries_dependency_attribute, NULL },
+  { "pre", 0, -1, false, false, false, false,
+    handle_contract_attribute, NULL },
+  { "post", 0, -1, false, false, false, false,
+    handle_contract_attribute, NULL },
   { NULL, 0, 0, false, false, false, false, NULL, NULL }
 };
 
@@ -5306,6 +5362,17 @@ handle_abi_tag_attribute (tree* node, tree name, tree args,
   return NULL_TREE;
 }
 
+/* Perform checking for contract attributes.  */
+
+tree
+handle_contract_attribute (tree *ARG_UNUSED (node), tree ARG_UNUSED (name),
+			   tree ARG_UNUSED (args), int ARG_UNUSED (flags),
+			   bool *ARG_UNUSED (no_add_attrs))
+{
+  /* TODO: Is there any checking we could do here?  */
+  return NULL_TREE;
+}
+
 /* Return a new PTRMEM_CST of the indicated TYPE.  The MEMBER is the
    thing pointed to by the constant.  */