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c++: reinterpret_cast from prvalue to rvalue ref [PR98440]

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In r260622 I allowed this under the general principle that [basic.lval]
"Whenever a prvalue appears as an operand of an operator that expects a
glvalue for that operand, the temporary materialization conversion (7.3.4)
is applied to convert the expression to an xvalue."  But
[expr.reinterpret.cast] specifically excludes creating a temporary in this
case.

gcc/cp/ChangeLog:

	PR c++/98440
	* typeck.c (build_reinterpret_cast_1): Don't perform
	temporary materialization.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/rv-cast6.C: Expect reinterpret_cast error.
	* g++.dg/cpp0x/reinterpret_cast2.C: Adjust message.
	* g++.old-deja/g++.jason/rvalue3.C: Likewise.
This commit is contained in:
Jason Merrill 2021-04-05 15:50:48 -04:00
parent 9f4c41147a
commit 07f56824fd
4 changed files with 10 additions and 14 deletions
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18
gcc/cp/typeck.c
View file

@ -7938,22 +7938,18 @@ build_reinterpret_cast_1 (location_t loc, tree type, tree expr,
type = cv_unqualified (type);
/* [expr.reinterpret.cast]
A glvalue expression of type T1 can be cast to the type
A glvalue of type T1, designating an object x, can be cast to the type
"reference to T2" if an expression of type "pointer to T1" can be
explicitly converted to the type "pointer to T2" using a
reinterpret_cast. */
explicitly converted to the type "pointer to T2" using a reinterpret_cast.
The result is that of *reinterpret_cast<T2 *>(p) where p is a pointer to x
of type "pointer to T1". No temporary is created, no copy is made, and no
constructors (11.4.4) or conversion functions (11.4.7) are called. */
if (TYPE_REF_P (type))
{
if (TYPE_REF_IS_RVALUE (type) && !VOID_TYPE_P (intype))
{
if (!obvalue_p (expr))
/* Perform the temporary materialization conversion. */
expr = get_target_expr_sfinae (expr, complain);
}
else if (!lvalue_p (expr))
if (!glvalue_p (expr))
{
if (complain & tf_error)
error_at (loc, "invalid cast of an rvalue expression of type "
error_at (loc, "invalid cast of a prvalue expression of type "
"%qT to type %qT",
intype, type);
return error_mark_node;

2
gcc/testsuite/g++.dg/cpp0x/reinterpret_cast2.C
View file

@ -6,5 +6,5 @@ struct S { };
void
foo ()
{
auto a = reinterpret_cast<S&&>(foo ()); // { dg-error "12:invalid cast of an rvalue expression of type 'void' to type" }
auto a = reinterpret_cast<S&&>(foo ()); // { dg-error "12:invalid cast of a prvalue expression of type 'void' to type" }
}

2
gcc/testsuite/g++.dg/cpp0x/rv-cast6.C
View file

@ -5,7 +5,7 @@ struct A { virtual void f(); };
struct B : A {};
auto && a = static_cast<A&&>(B());
auto && b = reinterpret_cast<A&&>(B());
auto && b = reinterpret_cast<A&&>(B()); // { dg-error "prvalue" }
auto && c = dynamic_cast<A&&>(B());
auto && d = dynamic_cast<B&&>(static_cast<A&&>(B()));
auto && e = const_cast<B&&>(B());

2
gcc/testsuite/g++.old-deja/g++.jason/rvalue3.C
View file

@ -2,5 +2,5 @@
int main ()
{
int i;
int &ir = (int&)(int)i; // { dg-error "14:invalid cast of an rvalue expression" } casting rvalue to reference type
int &ir = (int&)(int)i; // { dg-error "14:invalid cast of a prvalue expression" } casting rvalue to reference type
}