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c++: value category of compound object expr [PR104173]

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Here the call to (the &&-qualified) toLower() is incorrectly rejected
during overload resolution because the object expression is encoded as
an lvalue when it's really a prvalue.  The object expression,
instance()->applicationName(), is encoded as an INDIRECT_REF of a
COMPOUND_EXPR

  *(*instance ();, &TARGET_EXPR <D.2383, QCoreApplication::applicationName ()>;);

which lvalue_kind deems an lvalue.

This issue is similar to PR88103 except that here the original compound
object expression is a prvalue rather than an xvalue.  The fix there was to
adjust the result of unary_complex_lvalue in build_class_member_access_expr
so that xvalueness of the original expression is preserved.  This patch
extends that fix so that rvalueness is preserved more generally.

	PR c++/104173

gcc/cp/ChangeLog:

	* typeck.cc (build_class_member_access_expr): Extend
	unary_complex_lvalue result adjustment to preserve all
	rvalues, not just xvalues.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/ref-qual21.C: New test.
This commit is contained in:
Patrick Palka 2022-01-24 09:17:35 -05:00
parent 978abe918f
commit 2a908f3da0
2 changed files with 31 additions and 11 deletions
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19
gcc/cp/typeck.cc
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@ -2726,17 +2726,14 @@ build_class_member_access_expr (cp_expr object, tree member,
/* Transform `(a, b).x' into `(*(a, &b)).x', `(a ? b : c).x' into
`(*(a ? &b : &c)).x', and so on. A COND_EXPR is only an lvalue
in the front end; only _DECLs and _REFs are lvalues in the back end. */
{
tree temp = unary_complex_lvalue (ADDR_EXPR, object);
if (temp)
{
temp = cp_build_fold_indirect_ref (temp);
if (xvalue_p (object) && !xvalue_p (temp))
/* Preserve xvalue kind. */
temp = move (temp);
object = temp;
}
}
if (tree temp = unary_complex_lvalue (ADDR_EXPR, object))
{
temp = cp_build_fold_indirect_ref (temp);
if (!lvalue_p (object) && lvalue_p (temp))
/* Preserve rvalueness. */
temp = move (temp);
object = temp;
}
/* In [expr.ref], there is an explicit list of the valid choices for
MEMBER. We check for each of those cases here. */

23
gcc/testsuite/g++.dg/cpp0x/ref-qual21.C Normal file
View file

@ -0,0 +1,23 @@
// PR c++/104173
// { dg-do compile { target c++11 } }
struct QString {
QString toLower() &&;
};
struct QCoreApplication {
static QString applicationName();
};
QCoreApplication* instance();
void f() {
instance()->applicationName().toLower();
}
template<class...>
void g() {
instance()->applicationName().toLower();
}
template void g<>();