PR c++/91264 - detect modifying const objects in constexpr.
* constexpr.c (modifying_const_object_error): New function. (cxx_eval_call_expression): Set TREE_READONLY on a CONSTRUCTOR of a const-qualified object after it's been fully constructed. (modifying_const_object_p): New function. (cxx_eval_store_expression): Detect modifying a const object during constant expression evaluation. (cxx_eval_increment_expression): Use a better location when building up the store. (cxx_eval_constant_expression) <case DECL_EXPR>: Mark a constant object's constructor TREE_READONLY. * g++.dg/cpp1y/constexpr-tracking-const1.C: New test. * g++.dg/cpp1y/constexpr-tracking-const2.C: New test. * g++.dg/cpp1y/constexpr-tracking-const3.C: New test. * g++.dg/cpp1y/constexpr-tracking-const4.C: New test. * g++.dg/cpp1y/constexpr-tracking-const5.C: New test. * g++.dg/cpp1y/constexpr-tracking-const6.C: New test. * g++.dg/cpp1y/constexpr-tracking-const7.C: New test. * g++.dg/cpp1y/constexpr-tracking-const8.C: New test. * g++.dg/cpp1y/constexpr-tracking-const9.C: New test. * g++.dg/cpp1y/constexpr-tracking-const10.C: New test. * g++.dg/cpp1y/constexpr-tracking-const11.C: New test. * g++.dg/cpp1y/constexpr-tracking-const12.C: New test. * g++.dg/cpp1y/constexpr-tracking-const13.C: New test. * g++.dg/cpp1y/constexpr-tracking-const14.C: New test. From-SVN: r274671
This commit is contained in:
Marek Polacek
Marek Polacek
parent
5a9ea4fff4
commit
04e1749c55
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@ -1,3 +1,17 @@
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2019-08-19 Marek Polacek <polacek@redhat.com>
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PR c++/91264 - detect modifying const objects in constexpr.
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* constexpr.c (modifying_const_object_error): New function.
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(cxx_eval_call_expression): Set TREE_READONLY on a CONSTRUCTOR of
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a const-qualified object after it's been fully constructed.
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(modifying_const_object_p): New function.
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(cxx_eval_store_expression): Detect modifying a const object
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during constant expression evaluation.
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(cxx_eval_increment_expression): Use a better location when building
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up the store.
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(cxx_eval_constant_expression) <case DECL_EXPR>: Mark a constant
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object's constructor TREE_READONLY.
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2019-08-15 Jason Merrill <jason@redhat.com>
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PR c++/90393 - ICE with thow in ?:
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@ -1575,6 +1575,19 @@ clear_no_implicit_zero (tree ctor)
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}
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}
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/* Complain about a const object OBJ being modified in a constant expression.
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EXPR is the MODIFY_EXPR expression performing the modification. */
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static void
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modifying_const_object_error (tree expr, tree obj)
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{
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location_t loc = cp_expr_loc_or_input_loc (expr);
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auto_diagnostic_group d;
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error_at (loc, "modifying a const object %qE is not allowed in "
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"a constant expression", TREE_OPERAND (expr, 0));
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inform (location_of (obj), "originally declared %<const%> here");
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}
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/* Subroutine of cxx_eval_constant_expression.
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Evaluate the call expression tree T in the context of OLD_CALL expression
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evaluation. */
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@ -1775,6 +1788,19 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
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depth_ok = push_cx_call_context (t);
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/* Remember the object we are constructing. */
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tree new_obj = NULL_TREE;
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if (DECL_CONSTRUCTOR_P (fun))
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{
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/* In a constructor, it should be the first `this' argument.
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At this point it has already been evaluated in the call
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to cxx_bind_parameters_in_call. */
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new_obj = TREE_VEC_ELT (new_call.bindings, 0);
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STRIP_NOPS (new_obj);
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if (TREE_CODE (new_obj) == ADDR_EXPR)
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new_obj = TREE_OPERAND (new_obj, 0);
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}
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tree result = NULL_TREE;
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constexpr_call *entry = NULL;
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@ -1910,6 +1936,23 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
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}
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}
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/* At this point, the object's constructor will have run, so
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the object is no longer under construction, and its possible
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'const' semantics now apply. Make a note of this fact by
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marking the CONSTRUCTOR TREE_READONLY. */
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if (new_obj
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&& CLASS_TYPE_P (TREE_TYPE (new_obj))
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&& CP_TYPE_CONST_P (TREE_TYPE (new_obj)))
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{
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/* Subobjects might not be stored in ctx->values but we can
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get its CONSTRUCTOR by evaluating *this. */
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tree e = cxx_eval_constant_expression (ctx, new_obj,
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/*lval*/false,
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non_constant_p,
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overflow_p);
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TREE_READONLY (e) = true;
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}
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/* Forget the saved values of the callee's SAVE_EXPRs. */
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unsigned int i;
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tree save_expr;
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@ -3724,6 +3767,26 @@ maybe_simplify_trivial_copy (tree &target, tree &init)
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}
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}
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/* Return true if we are modifying something that is const during constant
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expression evaluation. CODE is the code of the statement, OBJ is the
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object in question, MUTABLE_P is true if one of the subobjects were
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declared mutable. */
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static bool
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modifying_const_object_p (tree_code code, tree obj, bool mutable_p)
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{
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/* If this is initialization, there's no problem. */
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if (code != MODIFY_EXPR)
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return false;
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/* [basic.type.qualifier] "A const object is an object of type
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const T or a non-mutable subobject of a const object." */
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if (mutable_p)
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return false;
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return (TREE_READONLY (obj) || CP_TYPE_CONST_P (TREE_TYPE (obj)));
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}
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/* Evaluate an INIT_EXPR or MODIFY_EXPR. */
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static tree
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@ -3773,6 +3836,9 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t,
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/* Find the underlying variable. */
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releasing_vec refs;
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tree object = NULL_TREE;
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/* If we're modifying a const object, save it. */
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tree const_object_being_modified = NULL_TREE;
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bool mutable_p = false;
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for (tree probe = target; object == NULL_TREE; )
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{
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switch (TREE_CODE (probe))
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@ -3783,6 +3849,12 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t,
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{
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tree ob = TREE_OPERAND (probe, 0);
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tree elt = TREE_OPERAND (probe, 1);
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if (DECL_P (elt) && DECL_MUTABLE_P (elt))
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mutable_p = true;
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if (evaluated
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&& modifying_const_object_p (TREE_CODE (t), probe, mutable_p)
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&& const_object_being_modified == NULL_TREE)
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const_object_being_modified = probe;
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if (TREE_CODE (probe) == ARRAY_REF)
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{
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elt = eval_and_check_array_index (ctx, probe, false,
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@ -3811,6 +3883,10 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t,
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}
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}
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if (modifying_const_object_p (TREE_CODE (t), object, mutable_p)
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&& const_object_being_modified == NULL_TREE)
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const_object_being_modified = object;
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/* And then find/build up our initializer for the path to the subobject
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we're initializing. */
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tree *valp;
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@ -3950,6 +4026,62 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t,
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valp = &cep->value;
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}
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/* Detect modifying a constant object in constexpr evaluation.
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We have found a const object that is being modified. Figure out
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if we need to issue an error. Consider
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struct A {
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int n;
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constexpr A() : n(1) { n = 2; } // #1
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};
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struct B {
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const A a;
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constexpr B() { a.n = 3; } // #2
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};
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constexpr B b{};
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#1 is OK, since we're modifying an object under construction, but
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#2 is wrong, since "a" is const and has been fully constructed.
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To track it, we use the TREE_READONLY bit in the object's CONSTRUCTOR
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which means that the object is read-only. For the example above, the
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*ctors stack at the point of #2 will look like:
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ctors[0] = {.a={.n=2}} TREE_READONLY = 0
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ctors[1] = {.n=2} TREE_READONLY = 1
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and we're modifying "b.a", so we search the stack and see if the
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constructor for "b.a" has already run. */
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if (const_object_being_modified)
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{
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bool fail = false;
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if (!CLASS_TYPE_P (TREE_TYPE (const_object_being_modified)))
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fail = true;
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else
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{
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/* [class.ctor]p5 "A constructor can be invoked for a const,
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volatile, or const volatile object. const and volatile
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semantics are not applied on an object under construction.
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They come into effect when the constructor for the most
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derived object ends." */
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tree elt;
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unsigned int i;
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FOR_EACH_VEC_ELT (*ctors, i, elt)
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if (same_type_ignoring_top_level_qualifiers_p
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(TREE_TYPE (const_object_being_modified), TREE_TYPE (elt)))
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{
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fail = TREE_READONLY (elt);
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break;
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}
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}
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if (fail)
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{
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if (!ctx->quiet)
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modifying_const_object_error (t, const_object_being_modified);
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*non_constant_p = true;
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return t;
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}
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}
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if (!preeval)
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{
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/* Create a new CONSTRUCTOR in case evaluation of the initializer
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@ -4063,7 +4195,8 @@ cxx_eval_increment_expression (const constexpr_ctx *ctx, tree t,
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VERIFY_CONSTANT (mod);
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/* Storing the modified value. */
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tree store = build2 (MODIFY_EXPR, type, op, mod);
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tree store = build2_loc (cp_expr_loc_or_loc (t, input_location),
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MODIFY_EXPR, type, op, mod);
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cxx_eval_constant_expression (ctx, store,
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true, non_constant_p, overflow_p);
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ggc_free (store);
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@ -4650,6 +4783,11 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
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non_constant_p, overflow_p);
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/* Don't share a CONSTRUCTOR that might be changed. */
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init = unshare_constructor (init);
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/* Remember that a constant object's constructor has already
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run. */
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if (CLASS_TYPE_P (TREE_TYPE (r))
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&& CP_TYPE_CONST_P (TREE_TYPE (r)))
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TREE_READONLY (init) = true;
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ctx->values->put (r, init);
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}
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else if (ctx == &new_ctx)
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@ -1,3 +1,21 @@
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2019-08-19 Marek Polacek <polacek@redhat.com>
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PR c++/91264 - detect modifying const objects in constexpr.
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* g++.dg/cpp1y/constexpr-tracking-const1.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const2.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const3.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const4.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const5.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const6.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const7.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const8.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const9.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const10.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const11.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const12.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const13.C: New test.
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* g++.dg/cpp1y/constexpr-tracking-const14.C: New test.
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2019-08-19 Eric Botcazou <ebotcazou@adacore.com>
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* gnat.dg/elab8.adb, gnat.dg/elab8_gen.adb,
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@ -0,0 +1,72 @@
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// PR c++/91264
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// { dg-do compile { target c++14 } }
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constexpr void
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mod (int &r)
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{
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r = 99; // { dg-error "modifying a const object" }
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}
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constexpr int
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fn1 ()
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{
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const int i = 0; // { dg-message "originally declared" }
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mod (const_cast<int &>(i)); // { dg-message "in .constexpr. expansion of " }
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return i;
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}
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constexpr int i1 = fn1 (); // { dg-message "in .constexpr. expansion of " }
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constexpr int
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fn2 ()
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{
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const int i = 5; // { dg-message "originally declared" }
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const_cast<int &>(i) = 10; // { dg-error "modifying a const object" }
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return i;
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}
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constexpr int i2 = fn2 (); // { dg-message "in .constexpr. expansion of " }
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constexpr int
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fn3 ()
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{
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const int i = 5; // { dg-message "originally declared" }
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++const_cast<int &>(i); // { dg-error "modifying a const object" }
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return i;
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}
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constexpr int i3 = fn3 (); // { dg-message "in .constexpr. expansion of " }
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constexpr int
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fn4 ()
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{
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const int i = 5; // { dg-message "originally declared" }
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const_cast<int &>(i)--; // { dg-error "modifying a const object" }
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return i;
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}
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constexpr int i4 = fn4 (); // { dg-message "in .constexpr. expansion of " }
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constexpr int
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fn5 ()
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{
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const int i = 5; // { dg-message "originally declared" }
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const_cast<int &>(i) += 2; // { dg-error "modifying a const object" }
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return i;
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}
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constexpr int i5 = fn5 (); // { dg-message "in .constexpr. expansion of " }
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constexpr int
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fn6 ()
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{
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// This is OK.
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int i = 3;
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const int *cip = &i;
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int *ip = const_cast<int *>(cip);
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*ip = 4;
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return i;
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}
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constexpr int i6 = fn6 ();
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static_assert(i6 == 4, "");
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@ -0,0 +1,22 @@
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// PR c++/91264
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// { dg-do compile { target c++14 } }
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struct B {
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B() = default;
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int i;
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};
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constexpr B bar()
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{
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constexpr B b = B(); // { dg-message "originally declared" }
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B *p = const_cast<B*>(&b);
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p->i = 11; // { dg-error "modifying a const object" }
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return *p;
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}
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void foo()
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{
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constexpr B y = bar(); // { dg-message "in .constexpr. expansion of" }
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}
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@ -0,0 +1,16 @@
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// PR c++/91264
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// { dg-do compile { target c++14 } }
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struct S {
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int a = 1;
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int * ptr = &a;
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};
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constexpr bool f() {
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auto const s = S{}; // { dg-message "originally declared" }
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*s.ptr = 2; // { dg-error "modifying a const object" }
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return s.a == 2;
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}
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static_assert(f(), ""); // { dg-error "non-constant condition" }
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// { dg-message "in 'constexpr' expansion of" "" { target *-*-* } .-1 }
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@ -0,0 +1,17 @@
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// PR c++/91264
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// { dg-do compile { target c++14 } }
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struct A {
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const int n;
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int m;
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constexpr A() : n(1), m(2) { }
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};
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struct B {
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A a;
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constexpr B() {
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int *p = &a.m;
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*p = 3;
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}
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};
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constexpr B b;
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static_assert(b.a.m == 3, "");
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@ -0,0 +1,20 @@
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// PR c++/91264
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// { dg-do compile { target c++14 } }
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struct A {
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mutable int i;
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constexpr A() : i(0) { }
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};
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struct B {
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A a;
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constexpr B() : a{} { }
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};
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constexpr void
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g ()
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{
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const B b;
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b.a.i = 42;
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}
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static_assert((g(), 1), "");
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@ -0,0 +1,38 @@
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// PR c++/91264
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// { dg-do compile { target c++14 } }
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struct F {
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const int f;
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constexpr F() : f(9) { }
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};
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struct C {
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int n;
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const F f;
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constexpr C() : n(1) { n = 66; }
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};
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struct A {
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int r;
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const C c;
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constexpr A() : r(11) { r = 14; const_cast<C &>(c).n = 42; } // { dg-error "modifying a const object" }
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};
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struct D {
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const A a;
|
||||
constexpr D() { } // { dg-message "in .constexpr. expansion of" }
|
||||
};
|
||||
|
||||
struct E {
|
||||
const D d;
|
||||
constexpr E() { } // { dg-message "in .constexpr. expansion of" }
|
||||
};
|
||||
|
||||
struct B {
|
||||
const E e;
|
||||
constexpr B(bool) { } // { dg-message "in .constexpr. expansion of" }
|
||||
};
|
||||
|
||||
constexpr B b(false); // { dg-message "in .constexpr. expansion of" }
|
||||
// { dg-message "originally declared" "" { target *-*-* } .-1 }
|
||||
static_assert(b.e.d.a.c.n == 2, ""); // { dg-error "non-constant condition" }
|
||||
|
|
@ -0,0 +1,23 @@
|
|||
// PR c++/91264
|
||||
// { dg-do compile { target c++14 } }
|
||||
|
||||
struct X {
|
||||
int j;
|
||||
constexpr X() : j(0) { }
|
||||
};
|
||||
|
||||
struct Y {
|
||||
X x;
|
||||
constexpr Y() : x{} { }
|
||||
};
|
||||
|
||||
constexpr void
|
||||
g ()
|
||||
{
|
||||
const Y y; // { dg-message "originally declared" }
|
||||
Y *p = const_cast<Y *>(&y);
|
||||
p->x.j = 99; // { dg-error "modifying a const object" }
|
||||
}
|
||||
|
||||
static_assert((g() , 1), ""); // { dg-error "non-constant condition" }
|
||||
// { dg-message "in 'constexpr' expansion of" "" { target *-*-* } .-1 }
|
||||
|
|
@ -0,0 +1,22 @@
|
|||
// PR c++/91264
|
||||
// { dg-do compile { target c++14 } }
|
||||
|
||||
struct A {
|
||||
int n;
|
||||
constexpr A() : n(1) { n = 2; }
|
||||
};
|
||||
|
||||
struct B {
|
||||
const A a;
|
||||
constexpr B(bool b) {
|
||||
if (b)
|
||||
const_cast<A &>(a).n = 3; // { dg-error "modifying a const object" }
|
||||
}
|
||||
};
|
||||
|
||||
constexpr B b(false);
|
||||
static_assert(b.a.n == 2, "");
|
||||
|
||||
constexpr B b2(true); // { dg-message "in .constexpr. expansion of " }
|
||||
// { dg-message "originally declared" "" { target *-*-* } .-1 }
|
||||
static_assert((b2.a.n, 1), "");
|
||||
|
|
@ -0,0 +1,17 @@
|
|||
// PR c++/91264
|
||||
// { dg-do compile { target c++14 } }
|
||||
|
||||
struct A {
|
||||
const int n;
|
||||
constexpr A() : n(1) { }
|
||||
};
|
||||
struct B {
|
||||
A a;
|
||||
constexpr B() {
|
||||
int *p = const_cast<int *>(&a.n);
|
||||
*p = 3; // { dg-error "modifying a const object" }
|
||||
}
|
||||
};
|
||||
constexpr B b; // { dg-message "in .constexpr. expansion of " }
|
||||
// { dg-message "originally declared" "" { target *-*-* } .-1 }
|
||||
static_assert((b.a.n, 1), "");
|
||||
|
|
@ -0,0 +1,17 @@
|
|||
// PR c++/91264
|
||||
// { dg-do compile { target c++14 } }
|
||||
|
||||
struct A {
|
||||
mutable int n;
|
||||
constexpr A() : n(1) { n = 2; }
|
||||
};
|
||||
|
||||
struct B {
|
||||
const A a;
|
||||
constexpr B() {
|
||||
const_cast<A &>(a).n = 3;
|
||||
}
|
||||
};
|
||||
|
||||
constexpr B b{};
|
||||
static_assert((b.a.n, 1), "");
|
||||
|
|
@ -0,0 +1,22 @@
|
|||
// PR c++/91264
|
||||
// { dg-do compile { target c++14 } }
|
||||
|
||||
struct X {
|
||||
mutable int j;
|
||||
constexpr X() : j(0) { }
|
||||
};
|
||||
|
||||
struct Y {
|
||||
X x;
|
||||
constexpr Y() : x{} { }
|
||||
};
|
||||
|
||||
constexpr void
|
||||
g ()
|
||||
{
|
||||
const Y y;
|
||||
Y *p = const_cast<Y *>(&y);
|
||||
p->x.j = 99;
|
||||
}
|
||||
|
||||
static_assert((g(), 1), "");
|
||||
|
|
@ -0,0 +1,23 @@
|
|||
// PR c++/91264
|
||||
// { dg-do compile { target c++14 } }
|
||||
|
||||
struct D { int n; };
|
||||
|
||||
struct C { const D d; };
|
||||
|
||||
struct A {
|
||||
C c;
|
||||
constexpr A() : c{} { }
|
||||
};
|
||||
|
||||
struct B {
|
||||
A a;
|
||||
constexpr B() {
|
||||
int &r = const_cast<int &>(a.c.d.n);
|
||||
r = 3; // { dg-error "modifying a const object" }
|
||||
}
|
||||
};
|
||||
|
||||
constexpr B b{}; // { dg-message "in .constexpr. expansion of " }
|
||||
// { dg-message "originally declared" "" { target *-*-* } .-1 }
|
||||
static_assert((b.a.c.d.n, 1), "");
|
||||
|
|
@ -0,0 +1,23 @@
|
|||
// PR c++/91264
|
||||
// { dg-do compile { target c++14 } }
|
||||
|
||||
struct B {
|
||||
int i;
|
||||
double d;
|
||||
};
|
||||
|
||||
constexpr B bar()
|
||||
{
|
||||
constexpr B b = {10,10.10}; // { dg-message "originally declared" }
|
||||
B *p = const_cast<B*>(&b);
|
||||
|
||||
p->i = 11; // { dg-error "modifying a const object" }
|
||||
p->d = 11.11;
|
||||
|
||||
return *p;
|
||||
}
|
||||
|
||||
void foo()
|
||||
{
|
||||
constexpr B y = bar(); // { dg-message "in .constexpr. expansion of" }
|
||||
}
|
||||
|
|
@ -0,0 +1,23 @@
|
|||
// PR c++/91264
|
||||
// { dg-do compile { target c++14 } }
|
||||
|
||||
struct B {
|
||||
int i;
|
||||
double d;
|
||||
};
|
||||
|
||||
constexpr B bar()
|
||||
{
|
||||
constexpr B b{}; // { dg-message "originally declared" }
|
||||
B *p = const_cast<B*>(&b);
|
||||
|
||||
p->i = 11; // { dg-error "modifying a const object" }
|
||||
p->d = 11.11;
|
||||
|
||||
return *p;
|
||||
}
|
||||
|
||||
void foo()
|
||||
{
|
||||
constexpr B y = bar(); // { dg-message "in .constexpr. expansion of" }
|
||||
}
|
||||
Loading…
Reference in New Issue