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
