In the first testcase below, the call to the target constructor foo{} from foo's
delegating constructor is encoded as the INIT_EXPR
*(struct foo *) this = AGGR_INIT_EXPR <4, __ct_comp, D.2140, ...>;
During initialization of the variable 'bar', we prematurely set TREE_READONLY on
bar's CONSTRUCTOR in two places before the outer delegating constructor has
returned: first, at the end of cxx_eval_call_expression after evaluating the RHS
of the above INIT_EXPR, and second, at the end of cxx_eval_store_expression
after having finished evaluating the above INIT_EXPR. This then prevents the
rest of the outer delegating constructor from mutating 'bar'.
This (hopefully minimally risky) patch makes cxx_eval_call_expression refrain
from setting TREE_READONLY when evaluating the target constructor of a
delegating constructor. It also makes cxx_eval_store_expression refrain from
setting TREE_READONLY when the object being initialized is "*this', on the basis
that it should be the responsibility of the routine that set 'this' in the first
place to set the object's TREE_READONLY appropriately.
gcc/cp/ChangeLog:
PR c++/94772
* constexpr.c (cxx_eval_call_expression): Don't set new_obj if we're
evaluating the target constructor of a delegating constructor.
(cxx_eval_store_expression): Don't set TREE_READONLY if the LHS of the
INIT_EXPR is '*this'.
gcc/testsuite/ChangeLog:
PR c++/94772
* g++.dg/cpp1y/constexpr-tracking-const23.C: New test.
* g++.dg/cpp1y/constexpr-tracking-const24.C: New test.
* g++.dg/cpp1y/constexpr-tracking-const25.C: New test.
+2020-04-27 Patrick Palka <ppalka@redhat.com>
+
+ PR c++/94772
+ * constexpr.c (cxx_eval_call_expression): Don't set new_obj if we're
+ evaluating the target constructor of a delegating constructor.
+ (cxx_eval_store_expression): Don't set TREE_READONLY if the LHS of the
+ INIT_EXPR is '*this'.
+
2020-04-26 Marek Polacek <polacek@redhat.com>
PR c++/90320
STRIP_NOPS (new_obj);
if (TREE_CODE (new_obj) == ADDR_EXPR)
new_obj = TREE_OPERAND (new_obj, 0);
+
+ if (ctx->call && ctx->call->fundef
+ && DECL_CONSTRUCTOR_P (ctx->call->fundef->decl))
+ {
+ tree cur_obj = TREE_VEC_ELT (ctx->call->bindings, 0);
+ STRIP_NOPS (cur_obj);
+ if (TREE_CODE (cur_obj) == ADDR_EXPR)
+ cur_obj = TREE_OPERAND (cur_obj, 0);
+ if (new_obj == cur_obj)
+ /* We're calling the target constructor of a delegating
+ constructor, or accessing a base subobject through a
+ NOP_EXPR as part of a call to a base constructor, so
+ there is no new (sub)object. */
+ new_obj = NULL_TREE;
+ }
}
tree result = NULL_TREE;
if (TREE_CODE (t) == INIT_EXPR
&& TREE_CODE (*valp) == CONSTRUCTOR
&& TYPE_READONLY (type))
- TREE_READONLY (*valp) = true;
+ {
+ if (INDIRECT_REF_P (target)
+ && (is_this_parameter
+ (tree_strip_nop_conversions (TREE_OPERAND (target, 0)))))
+ /* We've just initialized '*this' (perhaps via the target
+ constructor of a delegating constructor). Leave it up to the
+ caller that set 'this' to set TREE_READONLY appropriately. */
+ gcc_checking_assert (same_type_ignoring_top_level_qualifiers_p
+ (TREE_TYPE (target), type));
+ else
+ TREE_READONLY (*valp) = true;
+ }
/* Update TREE_CONSTANT and TREE_SIDE_EFFECTS on enclosing
CONSTRUCTORs, if any. */
+2020-04-27 Patrick Palka <ppalka@redhat.com>
+
+ PR c++/94772
+ * g++.dg/cpp1y/constexpr-tracking-const23.C: New test.
+ * g++.dg/cpp1y/constexpr-tracking-const24.C: New test.
+ * g++.dg/cpp1y/constexpr-tracking-const25.C: New test.
+
2020-04-27 Szabolcs Nagy <szabolcs.nagy@arm.com>
PR target/94697
--- /dev/null
+// PR c++/94772
+// { dg-do compile { target c++14 } }
+
+struct foo
+{
+ int x{};
+
+ constexpr foo() noexcept = default;
+
+ constexpr foo(int a) : foo{}
+ { x = -a; }
+
+ constexpr foo(int a, int b) : foo{a}
+ { x += a + b; }
+};
+
+int main()
+{
+ constexpr foo bar{1, 2};
+ static_assert(bar.x == 2, "");
+}
--- /dev/null
+// PR c++/94772
+// { dg-do compile { target c++14 } }
+
+struct base
+{
+ base() = default;
+
+ constexpr base(int) : base{} { }
+};
+
+struct foo : base
+{
+ int x{};
+
+ constexpr foo(int a) : base{a}
+ { x = -a; }
+
+ constexpr foo(int a, int b) : foo{a}
+ { x += a + b; }
+};
+
+int main()
+{
+ constexpr foo bar{1, 2};
+ static_assert(bar.x == 2, "");
+}
--- /dev/null
+// PR c++/94772
+// { dg-do compile { target c++14 } }
+
+template<int>
+struct base
+{
+ int y{};
+
+ base() = default;
+
+ constexpr base(int a) : base{}
+ { y = a; }
+};
+
+struct foo : base<1>, base<2>
+{
+ int x{};
+
+ constexpr foo() : base<2>{}
+ {
+ ++x; --x;
+ ++base<1>::y;
+ ++base<2>::y;
+ }
+
+ constexpr foo(int a) : base<2>{a}
+ {
+ x = -base<2>::y;
+ ++base<1>::y;
+ ++base<2>::y;
+ }
+
+ constexpr foo(int a, int b) : foo{a}
+ {
+ x += a + b;
+ ++base<1>::y;
+ ++base<2>::y;
+ }
+
+ constexpr foo(int a, int b, int c) : base<1>{a}
+ {
+ x += a + b + c;
+ ++base<1>::y;
+ ++base<2>::y;
+ }
+};
+
+#define SA(X) static_assert(X, #X)
+
+int main()
+{
+ constexpr foo bar1{1, 2};
+ SA( bar1.x == 2 );
+ SA( bar1.base<1>::y == 2 );
+ SA( bar1.base<2>::y == 3 );
+
+ constexpr foo bar2{1, 2, 3};
+ SA( bar2.x == 6 );
+ SA( bar2.base<1>::y == 2 );
+ SA( bar2.base<2>::y == 1 );
+
+ constexpr foo bar3{};
+ SA( bar3.x == 0 );
+ SA( bar3.base<1>::y == 1 );
+ SA( bar3.base<2>::y == 1 );
+}
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