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* [gcc r12-10109] c++: NRV and goto [PR92407]
@ 2024-01-24 19:40 Jason Merrill
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From: Jason Merrill @ 2024-01-24 19:40 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:193321d2649a818c3b322c8db79a2805cfdd7095
commit r12-10109-g193321d2649a818c3b322c8db79a2805cfdd7095
Author: Jason Merrill <jason@redhat.com>
Date: Sun Jun 4 12:00:55 2023 -0400
c++: NRV and goto [PR92407]
Here our named return value optimization was breaking the required
destructor when the goto takes 'a' out of scope. A simple fix for the
release branches is to disable the optimization in the presence of backward
goto.
We could do better by disabling the optimization only if there is a backward
goto across the variable declaration, but we don't track that, and in GCC 14
we instead make the goto work with NRV.
PR c++/92407
gcc/cp/ChangeLog:
* cp-tree.h (struct language_function): Add backward_goto.
* decl.cc (check_goto): Set it.
* typeck.cc (check_return_expr): Prevent NRV if set.
gcc/testsuite/ChangeLog:
* g++.dg/opt/nrv22.C: New test.
(cherry picked from commit a645347c19b07cc7abd7bf276c6769fc41afc932)
Diff:
---
gcc/cp/cp-tree.h | 1 +
gcc/cp/decl.cc | 2 ++
gcc/cp/typeck.cc | 3 +++
gcc/testsuite/g++.dg/opt/nrv22.C | 30 ++++++++++++++++++++++++++++++
4 files changed, 36 insertions(+)
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 5b3836422d6..132929375ea 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -2077,6 +2077,7 @@ struct GTY(()) language_function {
BOOL_BITFIELD invalid_constexpr : 1;
BOOL_BITFIELD throwing_cleanup : 1;
+ BOOL_BITFIELD backward_goto : 1;
hash_table<named_label_hash> *x_named_labels;
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 22060b11176..878b14fe771 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -3650,6 +3650,8 @@ check_goto (tree decl)
return;
}
+ cp_function_chain->backward_goto = true;
+
bool saw_catch = false, complained = false;
int identified = 0;
tree bad;
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 3be59f47179..6ca240fe40a 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -10678,6 +10678,9 @@ check_return_expr (tree retval, bool *no_warning)
if (fn_returns_value_p && flag_elide_constructors)
{
if (named_return_value_okay_p
+ /* The current NRV implementation breaks if a backward goto needs to
+ destroy the object (PR92407). */
+ && !cp_function_chain->backward_goto
&& (current_function_return_value == NULL_TREE
|| current_function_return_value == bare_retval))
current_function_return_value = bare_retval;
diff --git a/gcc/testsuite/g++.dg/opt/nrv22.C b/gcc/testsuite/g++.dg/opt/nrv22.C
new file mode 100644
index 00000000000..eb889fa615b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/nrv22.C
@@ -0,0 +1,30 @@
+// PR c++/92407
+// { dg-do run }
+
+struct A
+{
+ A () { a++; }
+ A (const A &) { a++; }
+ ~A () { a--; }
+ static int a;
+};
+int A::a = 0;
+
+A
+foo ()
+{
+ int cnt = 10;
+lab:
+ A a;
+ if (cnt--)
+ goto lab;
+ return a;
+}
+
+int
+main ()
+{
+ foo ();
+ if (A::a)
+ __builtin_abort ();
+}
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