Auto merge of #61872 - matthewjasper:refactor-mir-drop-gen, r=nikomatsakis

Clean up MIR drop generation

* Don't assign twice to the destination of a `while` loop containing a `break` expression
* Use `as_temp` to evaluate statement expression
* Avoid consecutive `StorageLive`s for the condition of a `while` loop
* Unify `return`, `break` and `continue` handling, and move it to `scopes.rs`
* Make some of the `scopes.rs` internals private
* Don't use `Place`s that are always `Local`s in MIR drop generation

Closes #42371
Closes #61579
Closes #61731
Closes #61834
Closes #61910
Closes #62115

src/test/ui/generator/issue-61442-stmt-expr-with-drop.rs

@@ -0,0 +1,32 @@
+// Test that we don't consider temporaries for statement expressions as live
+// across yields
+
+// check-pass
+// edition:2018
+
+#![feature(async_await, generators, generator_trait)]
+
+use std::ops::Generator;
+
+async fn drop_and_await() {
+    async {};
+    async {}.await;
+}
+
+fn drop_and_yield() {
+    let x = || {
+        String::new();
+        yield;
+    };
+    Box::pin(x).as_mut().resume();
+    let y = static || {
+        String::new();
+        yield;
+    };
+    Box::pin(y).as_mut().resume();
+}
+
+fn main() {
+    drop_and_await();
+    drop_and_yield();
+}

src/test/ui/nll/assign-while-to-immutable.rs

@@ -0,0 +1,11 @@
+// We used to incorrectly assign to `x` twice when generating MIR for this
+// function, preventing this from compiling.
+
+// check-pass
+
+fn main() {
+    let x = while false {
+        break;
+    };
+    let y = 'l: while break 'l {};
+}