[Bug c++/113789] [13/14 Regression] ICE on P2266/C++23 `decltype(throw x)` where x is move-eligible parameter
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113789
--- Comment #8 from GCC Commits ---
The trunk branch has been updated by Marek Polacek :
https://gcc.gnu.org/g:254ff3d0e34835b4de93d5e5763a7366dc7d989d
commit r14-9034-g254ff3d0e34835b4de93d5e5763a7366dc7d989d
Author: Marek Polacek
Date: Wed Feb 14 17:53:52 2024 -0500
c++: implicit move with throw [PR113853]
Here we have
template
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.
[Bug c++/113789] [13/14 Regression] ICE on P2266/C++23 `decltype(throw x)` where x is move-eligible parameter
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113789 --- Comment #7 from Marek Polacek --- The ICE was fixed by r14-8903-g3a3e0f1b46a3ad. But I'm not done here yet.
[Bug c++/113789] [13/14 Regression] ICE on P2266/C++23 `decltype(throw x)` where x is move-eligible parameter
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113789 --- Comment #6 from Arthur O'Dwyer --- (In reply to Marek Polacek from comment #5) > IOW, this should be accepted in C++23 but isn't (clang++ accepts in C++23): > [...] Correct, at least that's my intended interpretation. But the unexpected ICE was more dramatic. :) I'd be a tiny bit surprised if fixing `decltype(throw p)` actually closes the only pathway to that ICE; but if it does, then awesome, I have no complaints.
[Bug c++/113789] [13/14 Regression] ICE on P2266/C++23 `decltype(throw x)` where x is move-eligible parameter
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113789
--- Comment #5 from Marek Polacek ---
IOW, this should be accepted in C++23 but isn't (clang++ accepts in C++23):
struct AutoPtr {
AutoPtr() = default;
AutoPtr(AutoPtr&) {}
};
template auto f(T p, int) -> decltype(throw p, 1) = delete;
template void f(T p, long);
void
g ()
{
f (AutoPtr (), 42);
}
[Bug c++/113789] [13/14 Regression] ICE on P2266/C++23 `decltype(throw x)` where x is move-eligible parameter
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113789
--- Comment #4 from Marek Polacek ---
Um, that's not it. Since
struct AutoPtr {
AutoPtr() = default;
AutoPtr(AutoPtr&) {}
};
template int
f (T p)
{
throw p;
}
void
g ()
{
f (AutoPtr ());
}
is rejected in C++23, we probably should have rejected the decltype(throw p, 1)
candidate and never get to the throw in the body of the function f.
[Bug c++/113789] [13/14 Regression] ICE on P2266/C++23 `decltype(throw x)` where x is move-eligible parameter
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113789 --- Comment #3 from Marek Polacek --- I have a patch for the ICE (build_throw doesn't have a complain param so we wind up with "error reporting routines re-entered").
[Bug c++/113789] [13/14 Regression] ICE on P2266/C++23 `decltype(throw x)` where x is move-eligible parameter
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113789 Marek Polacek changed: What|Removed |Added Summary|ICE on P2266/C++23 |[13/14 Regression] ICE on |`decltype(throw x)` where x |P2266/C++23 `decltype(throw |is move-eligible parameter |x)` where x is ||move-eligible parameter Target Milestone|--- |13.3 Priority|P3 |P2
