c++: implicit move with throw [PR113853]
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Commit Message
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
Here we have
template<class T>
auto is_throwable(T t) -> decltype(throw t, true) { ... }
where we didn't properly mark 't' as IMPLICIT_RVALUE_P, which caused
the wrong overload to have been chosen. Jason figured out it's because
we don't correctly implement [expr.prim.id.unqual]#4.2, which post-P2266
says that an id-expression is move-eligible if
"the id-expression (possibly parenthesized) is the operand of
a throw-expression, and names an implicitly movable entity that belongs
to a scope that does not contain the compound-statement of the innermost
lambda-expression, try-block, or function-try-block (if any) whose
compound-statement or ctor-initializer contains the throw-expression."
I worked out that it's trying to say that given
struct X {
X();
X(const X&);
X(X&&) = delete;
};
the following should fail: the scope of the throw is an sk_try, and it's
also x's scope S, and S "does not contain the compound-statement of the
*try-block" so x is move-eligible, so we move, so we fail.
void f ()
try {
X x;
throw x; // use of deleted function
} catch (...) {
}
Whereas here:
void g (X x)
try {
throw x;
} catch (...) {
}
the throw is again in an sk_try, but x's scope is an sk_function_parms
which *does* contain the {} of the *try-block, so x is not move-eligible,
so we don't move, so we use X(const X&), and the code is fine.
The current code also doesn't seem to handle
void h (X x) {
void z (decltype(throw x, true));
}
where there's no enclosing lambda or sk_try so we should move.
I'm not doing anything about lambdas because we shouldn't reach the
code at the end of the function: the DECL_HAS_VALUE_EXPR_P check
shouldn't let us go further.
PR c++/113789
PR c++/113853
gcc/cp/ChangeLog:
* typeck.cc (treat_lvalue_as_rvalue_p): Update code to better
reflect [expr.prim.id.unqual]#4.2.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/sfinae69.C: Remove dg-bogus.
* g++.dg/cpp0x/sfinae70.C: New test.
* g++.dg/cpp0x/sfinae71.C: New test.
* g++.dg/cpp0x/sfinae72.C: New test.
* g++.dg/cpp2a/implicit-move4.C: New test.
---
gcc/cp/typeck.cc | 32 +++++------
gcc/testsuite/g++.dg/cpp0x/sfinae69.C | 2 +-
gcc/testsuite/g++.dg/cpp0x/sfinae70.C | 16 ++++++
gcc/testsuite/g++.dg/cpp0x/sfinae71.C | 17 ++++++
gcc/testsuite/g++.dg/cpp0x/sfinae72.C | 17 ++++++
gcc/testsuite/g++.dg/cpp2a/implicit-move4.C | 59 +++++++++++++++++++++
6 files changed, 126 insertions(+), 17 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/sfinae70.C
create mode 100644 gcc/testsuite/g++.dg/cpp0x/sfinae71.C
create mode 100644 gcc/testsuite/g++.dg/cpp0x/sfinae72.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/implicit-move4.C
base-commit: 5459a9074afabf700f055fc8164f88dadb1c39b0
Comments
On 2/15/24 10:19, Marek Polacek wrote:
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> -- >8 --
> Here we have
>
> template<class T>
> auto is_throwable(T t) -> decltype(throw t, true) { ... }
>
> where we didn't properly mark 't' as IMPLICIT_RVALUE_P, which caused
> the wrong overload to have been chosen. Jason figured out it's because
> we don't correctly implement [expr.prim.id.unqual]#4.2, which post-P2266
> says that an id-expression is move-eligible if
>
> "the id-expression (possibly parenthesized) is the operand of
> a throw-expression, and names an implicitly movable entity that belongs
> to a scope that does not contain the compound-statement of the innermost
> lambda-expression, try-block, or function-try-block (if any) whose
> compound-statement or ctor-initializer contains the throw-expression."
>
> I worked out that it's trying to say that given
>
> struct X {
> X();
> X(const X&);
> X(X&&) = delete;
> };
>
> the following should fail: the scope of the throw is an sk_try, and it's
> also x's scope S, and S "does not contain the compound-statement of the
> *try-block" so x is move-eligible, so we move, so we fail.
>
> void f ()
> try {
> X x;
> throw x; // use of deleted function
> } catch (...) {
> }
>
> Whereas here:
>
> void g (X x)
> try {
> throw x;
> } catch (...) {
> }
>
> the throw is again in an sk_try, but x's scope is an sk_function_parms
> which *does* contain the {} of the *try-block, so x is not move-eligible,
> so we don't move, so we use X(const X&), and the code is fine.
>
> The current code also doesn't seem to handle
>
> void h (X x) {
> void z (decltype(throw x, true));
> }
>
> where there's no enclosing lambda or sk_try so we should move.
>
> I'm not doing anything about lambdas because we shouldn't reach the
> code at the end of the function: the DECL_HAS_VALUE_EXPR_P check
> shouldn't let us go further.
>
> PR c++/113789
> PR c++/113853
>
> gcc/cp/ChangeLog:
>
> * typeck.cc (treat_lvalue_as_rvalue_p): Update code to better
> reflect [expr.prim.id.unqual]#4.2.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp0x/sfinae69.C: Remove dg-bogus.
> * g++.dg/cpp0x/sfinae70.C: New test.
> * g++.dg/cpp0x/sfinae71.C: New test.
> * g++.dg/cpp0x/sfinae72.C: New test.
> * g++.dg/cpp2a/implicit-move4.C: New test.
> ---
> gcc/cp/typeck.cc | 32 +++++------
> gcc/testsuite/g++.dg/cpp0x/sfinae69.C | 2 +-
> gcc/testsuite/g++.dg/cpp0x/sfinae70.C | 16 ++++++
> gcc/testsuite/g++.dg/cpp0x/sfinae71.C | 17 ++++++
> gcc/testsuite/g++.dg/cpp0x/sfinae72.C | 17 ++++++
> gcc/testsuite/g++.dg/cpp2a/implicit-move4.C | 59 +++++++++++++++++++++
> 6 files changed, 126 insertions(+), 17 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/sfinae70.C
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/sfinae71.C
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/sfinae72.C
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/implicit-move4.C
>
> diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
> index 132c55cfc6d..0dc44cd87ca 100644
> --- a/gcc/cp/typeck.cc
> +++ b/gcc/cp/typeck.cc
> @@ -10837,37 +10837,37 @@ treat_lvalue_as_rvalue_p (tree expr, bool return_p)
> parenthesized) id-expression that names an implicitly movable entity
> declared in the body or parameter-declaration-clause of the innermost
> enclosing function or lambda-expression, */
> - if (DECL_CONTEXT (retval) != current_function_decl)
> - return NULL_TREE;
> if (return_p)
> {
> + if (DECL_CONTEXT (retval) != current_function_decl)
> + return NULL_TREE;
> expr = move (expr);
> if (expr == error_mark_node)
> return NULL_TREE;
> return set_implicit_rvalue_p (expr);
> }
>
> - /* if the operand of a throw-expression is a (possibly parenthesized)
> - id-expression that names an implicitly movable entity whose scope does not
> - extend beyond the compound-statement of the innermost try-block or
> - function-try-block (if any) whose compound-statement or ctor-initializer
> - encloses the throw-expression, */
> + /* if the id-expression (possibly parenthesized) is the operand of
> + a throw-expression, and names an implicitly movable entity that belongs
> + to a scope that does not contain the compound-statement of the innermost
> + lambda-expression, try-block, or function-try-block (if any) whose
> + compound-statement or ctor-initializer contains the throw-expression. */
Please also mention here why you aren't checking for lambdas.
> /* C++20 added move on throw of parms. */
> if (TREE_CODE (retval) == PARM_DECL && cxx_dialect < cxx20)
> return NULL_TREE;
>
> for (cp_binding_level *b = current_binding_level;
> - ; b = b->level_chain)
> - {
> - for (tree decl = b->names; decl; decl = TREE_CHAIN (decl))
> - if (decl == retval)
> - return set_implicit_rvalue_p (move (expr));
> - if (b->kind == sk_function_parms
> - || b->kind == sk_try
> - || b->kind == sk_namespace)
> + b->kind != sk_namespace; b = b->level_chain)
> + if (b->kind == sk_try)
> + {
> + for (tree decl = b->names; decl; decl = TREE_CHAIN (decl))
> + if (decl == retval)
> + return set_implicit_rvalue_p (move (expr));
> return NULL_TREE;
> - }
What if the variable is in a block nested within the try-block? I think
we still want to walk b->names for every inner binding level.
Jason
@@ -10837,37 +10837,37 @@ treat_lvalue_as_rvalue_p (tree expr, bool return_p)
parenthesized) id-expression that names an implicitly movable entity
declared in the body or parameter-declaration-clause of the innermost
enclosing function or lambda-expression, */
- if (DECL_CONTEXT (retval) != current_function_decl)
- return NULL_TREE;
if (return_p)
{
+ if (DECL_CONTEXT (retval) != current_function_decl)
+ return NULL_TREE;
expr = move (expr);
if (expr == error_mark_node)
return NULL_TREE;
return set_implicit_rvalue_p (expr);
}
- /* if the operand of a throw-expression is a (possibly parenthesized)
- id-expression that names an implicitly movable entity whose scope does not
- extend beyond the compound-statement of the innermost try-block or
- function-try-block (if any) whose compound-statement or ctor-initializer
- encloses the throw-expression, */
+ /* if the id-expression (possibly parenthesized) is the operand of
+ a throw-expression, and names an implicitly movable entity that belongs
+ to a scope that does not contain the compound-statement of the innermost
+ lambda-expression, try-block, or function-try-block (if any) whose
+ compound-statement or ctor-initializer contains the throw-expression. */
/* C++20 added move on throw of parms. */
if (TREE_CODE (retval) == PARM_DECL && cxx_dialect < cxx20)
return NULL_TREE;
for (cp_binding_level *b = current_binding_level;
- ; b = b->level_chain)
- {
- for (tree decl = b->names; decl; decl = TREE_CHAIN (decl))
- if (decl == retval)
- return set_implicit_rvalue_p (move (expr));
- if (b->kind == sk_function_parms
- || b->kind == sk_try
- || b->kind == sk_namespace)
+ b->kind != sk_namespace; b = b->level_chain)
+ if (b->kind == sk_try)
+ {
+ for (tree decl = b->names; decl; decl = TREE_CHAIN (decl))
+ if (decl == retval)
+ return set_implicit_rvalue_p (move (expr));
return NULL_TREE;
- }
+ }
+
+ return set_implicit_rvalue_p (move (expr));
}
/* Warn about dubious usage of std::move (in a return statement, if RETURN_P
@@ -15,7 +15,7 @@ constexpr bool is_throwable(...) { return false; }
constexpr bool b = is_throwable<moveonly>(moveonly{});
#if __cplusplus >= 202002L
-static_assert (b, "move from the function parameter"); // { dg-bogus "" "PR113853" { xfail c++20 } }
+static_assert (b, "move from the function parameter");
#else
static_assert (!b, "no move from the function parameter");
#endif
new file mode 100644
@@ -0,0 +1,16 @@
+// PR c++/113789
+// { dg-do compile { target c++11 } }
+
+struct AutoPtr {
+ AutoPtr() = default;
+ AutoPtr(AutoPtr&) {}
+};
+
+template<class T> auto f(T p, int) -> decltype(throw p, 1) = delete;
+template<class T> void f(T p, long);
+
+void
+g ()
+{
+ f (AutoPtr (), 42); // { dg-error "use of deleted function" "" { target c++20_down } }
+}
new file mode 100644
@@ -0,0 +1,17 @@
+// PR c++/113789
+// { dg-do compile { target c++11 } }
+// Like sfinae70.C but T&&.
+
+struct AutoPtr {
+ AutoPtr() = default;
+ AutoPtr(AutoPtr&) {}
+};
+
+template<class T> auto f(T&& p, int) -> decltype(throw p, 1) = delete;
+template<class T> void f(T p, long);
+
+void
+g ()
+{
+ f (AutoPtr (), 42); // { dg-error "use of deleted function" "" { target c++20_down } }
+}
new file mode 100644
@@ -0,0 +1,17 @@
+// PR c++/113789
+// { dg-do compile { target c++11 } }
+// Like sfinae70.C but ().
+
+struct AutoPtr {
+ AutoPtr() = default;
+ AutoPtr(AutoPtr&) {}
+};
+
+template<class T> auto f(T p, int) -> decltype(throw (p), 1) = delete;
+template<class T> void f(T p, long);
+
+void
+g ()
+{
+ f (AutoPtr (), 42); // { dg-error "use of deleted function" "" { target c++20_down } }
+}
new file mode 100644
@@ -0,0 +1,59 @@
+// PR c++/113853
+// { dg-do compile { target c++20 } }
+
+struct X {
+ X();
+ X(const X&);
+ X(X&&) = delete;
+};
+
+void
+f1 ()
+{
+ try {
+ ;
+ } catch (X x) {
+ throw x; // { dg-error "use of deleted function" }
+ }
+}
+
+void
+f2 (X x)
+try {
+ ;
+} catch (...) {
+ throw x; // { dg-error "use of deleted function" }
+}
+
+void
+f3 ()
+try {
+ X x;
+ throw x; // { dg-error "use of deleted function" }
+} catch (...) {
+}
+
+void
+f4 (X x)
+try {
+ throw x;
+} catch (...) {
+}
+
+void
+f5 (X x)
+{
+ void g (decltype(throw x, true)); // { dg-error "use of deleted function|expected" }
+}
+
+// The "expected" shouldn't be here, c++/113924.
+void
+f6 (X x, int = decltype(throw x, true){}) // { dg-error "use of deleted function|expected" }
+{
+}
+
+void
+f7 (X x)
+{
+ [&] { throw x; };
+}