efriedma-quic wrote:
If I understand correctly, a "lifetime-extended" cleanup deals with the case of
a temporary whose lifetime continues beyond the expression. In other words, it
has different lifetimes depending on how you exit the expression: if the
variable's lifetime begins, it lasts until the end of that variable's lifetime.
Otherwise, it only lasts until the end of the full-expression. Due to the way
it's structured, the current mechanism only works correctly with thrown
exceptions; it doesn't work with other ways of exiting an expression. This
patch attempts to fix that.
Passing "0" to AddLifetimeExtendedCleanups() seems wrong. For example, suppose
you have the following:
```
int foo();
struct Printy {
~Printy() { }
};
struct Printies {
const Printy &a;
const Printy &b;
~Printies() {}
};
void f() {
Printies p2{
Printy(),
({
for (int i = 0; i < 10; ++i) {
Printies p3{
Printy(),
({
if(foo()) {
break;
}
Printy();
})};
}
Printy();
})};
}
```
The "break" needs to run some of the cleanups associated with lifetime-extended
temporaries... but not all of them.
We might want to consider making the whole process of lifetime extensions a bit
more explicit. Currently, we lazily construct the set of temporaries as we
evaluate the initializer, then reconstruct the cleanup stack at the end of the
full-expression to reflect the lifetime extension. Instead, we could have some
separate code to compute the list of lifetime-extended temporaries associated
with a given variable, and create cleanups for them before we start emitting
code for the initializer. That way, we don't need to mess with the cleanup
stack later; we just need to make sure we correctly skip executing the cleanups
which aren't supposed to run.
See also #12658.
https://github.com/llvm/llvm-project/pull/80698
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