Values moved in a match get dropped too late

[dotdash]

#15076 removed the extra alloca created for by-value bindings in a match. Unfortunately, that also changed at which point the value gets dropped. The previous (and IMHO desired/correct) behaviour was to drop the value when the match binding goes out of scope, but now the value gets dropped when the matched value goes out of scope.

Example:

struct S {
name: &'static str,
}

impl Drop for S {
    fn drop(&mut self) {
        println!("Dropping {}", self.name);
    }
}

pub fn main() {
    let matched = S { name: "Matched" };
    let outer = S { name: "Outer" };
    {
        match matched {
            s => {
            }
        }
        let inner = S { name: "Inner" }; 
    }
}

Output:

Old (rustc 0.11.0-pre (bab614f5fa725d248afc5f0530c835f37998ce8f 2014-06-25 08:06:21 +0000)):
===
Dropping Matched
Dropping Inner
Dropping Outer

New (rustc 0.11.0 (36d7d746c8366d78b332cffdff85318e709b38ca 2014-07-04 10:16:21 +0000)):
===
Dropping Inner
Dropping Outer
Dropping Matched

[dotdash]

This caused memory usage to go up quite a bit. Compiling librustc goes from hovering around 1GB and peaking around 1.6G to hovering around 2G and peaking and 2.5G.