Auto merge of #44480 - Zoxc:gen-liveness, r=arielb1

Analyse storage liveness and preserve it during generator transformation

This uses a dataflow analysis on `StorageLive` and `StorageDead` statements to infer where the storage of locals are live. The result of this analysis is intersected with the regular liveness analysis such that a local is can only be live when its storage is. This fixes https://github.com/rust-lang/rust/issues/44184. If the storage of a local is live across a suspension point, we'll insert a `StorageLive` statement for it after the suspension point so storage liveness is preserved. This fixes https://github.com/rust-lang/rust/issues/44179.

r? @arielb1

src/test/run-pass/generator/match-bindings.rs

@@ -0,0 +1,30 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(generators)]
+
+enum Enum {
+    A(String),
+    B
+}
+
+fn main() {
+    || {
+        loop {
+            if let true = true {
+                match Enum::A(String::new()) {
+                    Enum::A(_var) => {}
+                    Enum::B => {}
+                }
+            }
+            yield;
+        }
+    };
+}