https://gcc.gnu.org/g:42a4f863956c0bf18b97738da475bdb9c14504b2
commit r14-11498-g42a4f863956c0bf18b97738da475bdb9c14504b2
Author: Marek Polacek <pola...@redhat.com>
Date: Tue Mar 25 13:36:24 2025 -0400
c++: fix missing lifetime extension [PR119383]
Since r15-8011 cp_build_indirect_ref_1 won't do the *&TARGET_EXPR ->
TARGET_EXPR folding not to change its value category. That fix seems
correct but it made us stop extending the lifetime in this testcase,
causing a wrong-code issue -- extend_ref_init_temps_1 did not see
through the extra *& because it doesn't use a tree walk.
This patch reverts r15-8011 and instead handles the problem in
build_over_call by calling force_lvalue in the is_really_empty_class
case as well as in the general case.
PR c++/119383
gcc/cp/ChangeLog:
* call.cc (build_over_call): Use force_lvalue to ensure op= returns
an lvalue.
* cp-tree.h (force_lvalue): Declare.
* cvt.cc (force_lvalue): New.
* typeck.cc (cp_build_indirect_ref_1): Revert r15-8011.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/temp-extend3.C: New test.
Reviewed-by: Jason Merrill <ja...@redhat.com>
(cherry picked from commit e9803f10c9f376f6d091e7ef3ad6e1c92e7c8e8c)
Diff:
---
gcc/cp/call.cc | 9 +++++----
gcc/cp/cp-tree.h | 1 +
gcc/cp/cvt.cc | 13 +++++++++++++
gcc/cp/typeck.cc | 10 ++++------
gcc/testsuite/g++.dg/cpp0x/temp-extend3.C | 32 +++++++++++++++++++++++++++++++
5 files changed, 55 insertions(+), 10 deletions(-)
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 180afa6d053d..604b0b003a32 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -10519,10 +10519,8 @@ build_over_call (struct z_candidate *cand, int flags,
tsubst_flags_t complain)
if (is_really_empty_class (type, /*ignore_vptr*/true))
{
/* Avoid copying empty classes, but ensure op= returns an lvalue even
- if the object argument isn't one. This isn't needed in other cases
- since MODIFY_EXPR is always considered an lvalue. */
- to = cp_build_addr_expr (to, tf_none);
- to = cp_build_indirect_ref (input_location, to, RO_ARROW, complain);
+ if the object argument isn't one. */
+ to = force_lvalue (to, complain);
val = build2 (COMPOUND_EXPR, type, arg, to);
suppress_warning (val, OPT_Wunused);
}
@@ -10543,6 +10541,9 @@ build_over_call (struct z_candidate *cand, int flags,
tsubst_flags_t complain)
tree array_type, alias_set;
arg2 = TYPE_SIZE_UNIT (as_base);
+ /* Ensure op= returns an lvalue even if the object argument isn't
+ one. */
+ to = force_lvalue (to, complain);
to = cp_stabilize_reference (to);
arg0 = cp_build_addr_expr (to, complain);
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index a9a14d6267c8..cfdfc4f9abe7 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -6948,6 +6948,7 @@ extern tree convert_to_reference (tree, tree,
int, int, tree,
tsubst_flags_t);
extern tree convert_from_reference (tree);
extern tree force_rvalue (tree, tsubst_flags_t);
+extern tree force_lvalue (tree, tsubst_flags_t);
extern tree ocp_convert (tree, tree, int, int,
tsubst_flags_t);
extern tree cp_convert (tree, tree, tsubst_flags_t);
diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
index db086c017e89..b046010e7ff8 100644
--- a/gcc/cp/cvt.cc
+++ b/gcc/cp/cvt.cc
@@ -574,6 +574,19 @@ force_rvalue (tree expr, tsubst_flags_t complain)
return expr;
}
+/* Force EXPR to be an lvalue, if it isn't already. */
+
+tree
+force_lvalue (tree expr, tsubst_flags_t complain)
+{
+ if (!lvalue_p (expr))
+ {
+ expr = cp_build_addr_expr (expr, complain);
+ expr = cp_build_indirect_ref (input_location, expr, RO_ARROW, complain);
+ }
+ return expr;
+}
+
/* If EXPR and ORIG are INTEGER_CSTs, return a version of EXPR that has
TREE_OVERFLOW set only if it is set in ORIG. Otherwise, return EXPR
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 6e938f168a4c..7f97c9423f0a 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -3838,13 +3838,11 @@ cp_build_indirect_ref_1 (location_t loc, tree ptr,
ref_operator errorstring,
return error_mark_node;
}
else if (do_fold && TREE_CODE (pointer) == ADDR_EXPR
- && same_type_p (t, TREE_TYPE (TREE_OPERAND (pointer, 0)))
- /* Don't let this change the value category. '*&TARGET_EXPR'
- is an lvalue, but folding it into 'TARGET_EXPR' would turn
- it into a prvalue of class type. */
- && lvalue_p (TREE_OPERAND (pointer, 0)))
+ && same_type_p (t, TREE_TYPE (TREE_OPERAND (pointer, 0))))
/* The POINTER was something like `&x'. We simplify `*&x' to
- `x'. */
+ `x'. This can change the value category: '*&TARGET_EXPR'
+ is an lvalue and folding it into 'TARGET_EXPR' turns it into
+ a prvalue of class type. */
return TREE_OPERAND (pointer, 0);
else
{
diff --git a/gcc/testsuite/g++.dg/cpp0x/temp-extend3.C
b/gcc/testsuite/g++.dg/cpp0x/temp-extend3.C
new file mode 100644
index 000000000000..3eab88d0076e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/temp-extend3.C
@@ -0,0 +1,32 @@
+// PR c++/119383
+// { dg-do run { target c++11 } }
+
+int g;
+
+struct base {
+ virtual base *clone() const = 0;
+ ~base() { }
+};
+
+struct impl : virtual base {
+ base *clone() const { return new impl; } // #1
+ impl() { ++g; }
+ ~impl() { --g; }
+};
+
+const base *
+make_a_clone ()
+{
+ const base &base = impl{}; // #2
+ return base.clone();
+}
+
+int
+main ()
+{
+ make_a_clone ();
+ // impl::impl() is called twice (#1 and #2), impl::~impl() once,
+ // at the end of make_a_clone.
+ if (g != 1)
+ __builtin_abort ();
+}
