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/mir-opt/box_expr.rs

@@ -24,7 +24,7 @@ impl Drop for S {
 //     let mut _0: ();
 //     let _1: std::boxed::Box<S>;
 //     let mut _2: std::boxed::Box<S>;
-//     let mut _3: ();
+//     let _3: ();
 //     let mut _4: std::boxed::Box<S>;
 //     scope 1 {
 //     }
@@ -50,6 +50,7 @@ impl Drop for S {
 //
 //     bb4: {
 //         StorageDead(_2);
+//         StorageLive(_3);
 //         StorageLive(_4);
 //         _4 = move _1;
 //         _3 = const std::mem::drop::<std::boxed::Box<S>>(move _4) -> [return: bb5, unwind: bb7];
@@ -69,6 +70,7 @@ impl Drop for S {
 //
 //     bb8: {
 //         StorageDead(_4);
+//         StorageDead(_3);
 //         _0 = ();
 //         drop(_1) -> bb9;
 //     }

src/test/mir-opt/copy_propagation_arg.rs

@@ -61,12 +61,14 @@ fn main() {
 // END rustc.foo.CopyPropagation.after.mir
 // START rustc.bar.CopyPropagation.before.mir
 // bb0: {
+//     StorageLive(_2);
 //     StorageLive(_3);
 //     _3 = _1;
 //     _2 = const dummy(move _3) -> bb1;
 // }
 // bb1: {
 //     StorageDead(_3);
+//     StorageDead(_2);
 //     _1 = const 5u8;
 //     ...
 //     return;

src/test/mir-opt/generator-drop-cleanup.rs

@@ -18,6 +18,7 @@ fn main() {
 // }
 // bb1: {
 //     StorageDead(_3);
+//     StorageDead(_2);
 //     goto -> bb5;
 // }
 // bb2: {
@@ -36,6 +37,7 @@ fn main() {
 //     goto -> bb3;
 // }
 // bb7: {
+//     StorageLive(_2);
 //     StorageLive(_3);
 //     goto -> bb1;
 // }

src/test/mir-opt/generator-storage-dead-unwind.rs

@@ -54,6 +54,7 @@ fn main() {
 // }
 // bb2: {
 //     ...
+//     StorageLive(_6);
 //     StorageLive(_7);
 //     _7 = move _2;
 //     _6 = const take::<Foo>(move _7) -> [return: bb9, unwind: bb8];
@@ -81,16 +82,20 @@ fn main() {
 // }
 // bb8 (cleanup): {
 //     StorageDead(_7);
+//     StorageDead(_6);
 //     goto -> bb7;
 // }
 // bb9: {
 //     StorageDead(_7);
+//     StorageDead(_6);
+//     StorageLive(_8);
 //     StorageLive(_9);
 //     _9 = move _3;
 //     _8 = const take::<Bar>(move _9) -> [return: bb10, unwind: bb11];
 // }
 // bb10: {
 //     StorageDead(_9);
+//     StorageDead(_8);
 //     ...
 //     StorageDead(_3);
 //     StorageDead(_2);
@@ -98,6 +103,7 @@ fn main() {
 // }
 // bb11 (cleanup): {
 //     StorageDead(_9);
+//     StorageDead(_8);
 //     goto -> bb7;
 // }
 // bb12: {

src/test/mir-opt/issue-38669.rs

@@ -25,6 +25,7 @@ fn main() {
 //         falseUnwind -> [real: bb3, cleanup: bb1];
 //     }
 //     bb3: {
+//         StorageLive(_3);
 //         StorageLive(_4);
 //         _4 = _1;
 //         FakeRead(ForMatchedPlace, _4);
@@ -34,6 +35,7 @@ fn main() {
 //     bb5: {
 //         _3 = ();
 //         StorageDead(_4);
+//         StorageDead(_3);
 //         _1 = const true;
 //         _2 = ();
 //         goto -> bb2;
@@ -41,6 +43,7 @@ fn main() {
 //     bb6: {
 //         _0 = ();
 //         StorageDead(_4);
+//         StorageDead(_3);
 //         StorageDead(_1);
 //         return;
 //     }

src/test/mir-opt/issue-41110.rs

@@ -42,7 +42,7 @@ impl S {
 // START rustc.test.ElaborateDrops.after.mir
 //    let mut _0: ();
 //    let _1: S;
-//    let mut _3: ();
+//    let _3: ();
 //    let mut _4: S;
 //    let mut _5: S;
 //    let mut _6: bool;

src/test/mir-opt/issue-49232.rs

@@ -21,7 +21,7 @@ fn main() {
 //     let _2: i32;
 //     let mut _3: bool;
 //     let mut _4: !;
-//     let mut _5: ();
+//     let _5: ();
 //     let mut _6: &i32;
 //     scope 1 {
 //     }
@@ -73,12 +73,14 @@ fn main() {
 //     bb12: {
 //         FakeRead(ForLet, _2);
 //         StorageDead(_3);
+//         StorageLive(_5);
 //         StorageLive(_6);
 //         _6 = &_2;
 //         _5 = const std::mem::drop::<&i32>(move _6) -> [return: bb13, unwind: bb4];
 //     }
 //     bb13: {
 //         StorageDead(_6);
+//         StorageDead(_5);
 //         _1 = ();
 //         StorageDead(_2);
 //         goto -> bb1;

src/test/mir-opt/loop_test.rs

@@ -25,6 +25,7 @@ fn main() {
 //    bb3: { // Entry into the loop
 //        _1 = ();
 //        StorageDead(_2);
+//        StorageDead(_1);
 //        goto -> bb5;
 //    }
 //    ...

src/test/mir-opt/match-arm-scopes.rs

@@ -103,10 +103,6 @@ fn main() {
 // bb10: {                              // `else` block - first time
 //     _9 = (*_6);
 //     StorageDead(_10);
-//     FakeRead(ForMatchGuard, _3);
-//     FakeRead(ForMatchGuard, _4);
-//     FakeRead(ForGuardBinding, _6);
-//     FakeRead(ForGuardBinding, _8);
 //     switchInt(move _9) -> [false: bb16, otherwise: bb15];
 // }
 // bb11: {                              // `return 3` - first time
@@ -128,6 +124,10 @@ fn main() {
 // }
 // bb15: {
 //     StorageDead(_9);
+//     FakeRead(ForMatchGuard, _3);
+//     FakeRead(ForMatchGuard, _4);
+//     FakeRead(ForGuardBinding, _6);
+//     FakeRead(ForGuardBinding, _8);
 //     StorageLive(_5);
 //     _5 = (_2.1: bool);
 //     StorageLive(_7);
@@ -159,10 +159,6 @@ fn main() {
 // bb19: {                              // `else` block - second time
 //     _12 = (*_6);
 //     StorageDead(_13);
-//     FakeRead(ForMatchGuard, _3);
-//     FakeRead(ForMatchGuard, _4);
-//     FakeRead(ForGuardBinding, _6);
-//     FakeRead(ForGuardBinding, _8);
 //     switchInt(move _12) -> [false: bb22, otherwise: bb21];
 // }
 // bb20: {
@@ -175,6 +171,10 @@ fn main() {
 // }
 // bb21: {                              // bindings for arm 1
 //     StorageDead(_12);
+//     FakeRead(ForMatchGuard, _3);
+//     FakeRead(ForMatchGuard, _4);
+//     FakeRead(ForGuardBinding, _6);
+//     FakeRead(ForGuardBinding, _8);
 //     StorageLive(_5);
 //     _5 = (_2.0: bool);
 //     StorageLive(_7);

src/test/mir-opt/match_false_edges.rs

@@ -71,12 +71,12 @@ fn main() {
 //      _7 = const guard() -> [return: bb7, unwind: bb1];
 //  }
 //  bb7: { // end of guard
-//      FakeRead(ForMatchGuard, _4);
-//      FakeRead(ForGuardBinding, _6);
 //      switchInt(move _7) -> [false: bb9, otherwise: bb8];
 //  }
 //  bb8: { // arm1
 //      StorageDead(_7);
+//      FakeRead(ForMatchGuard, _4);
+//      FakeRead(ForGuardBinding, _6);
 //      StorageLive(_5);
 //      _5 = ((_2 as Some).0: i32);
 //      StorageLive(_8);
@@ -138,12 +138,12 @@ fn main() {
 //      _7 = const guard() -> [return: bb6, unwind: bb1];
 //  }
 //  bb6: { // end of guard
-//      FakeRead(ForMatchGuard, _4);
-//      FakeRead(ForGuardBinding, _6);
 //      switchInt(move _7) -> [false: bb8, otherwise: bb7];
 //  }
 //  bb7: {
 //      StorageDead(_7);
+//      FakeRead(ForMatchGuard, _4);
+//      FakeRead(ForGuardBinding, _6);
 //      StorageLive(_5);
 //      _5 = ((_2 as Some).0: i32);
 //      StorageLive(_8);
@@ -209,12 +209,12 @@ fn main() {
 //      _8 = const guard() -> [return: bb6, unwind: bb1];
 //  }
 //  bb6: { //end of guard1
-//      FakeRead(ForMatchGuard, _5);
-//      FakeRead(ForGuardBinding, _7);
 //      switchInt(move _8) -> [false: bb8, otherwise: bb7];
 //  }
 //  bb7: {
 //      StorageDead(_8);
+//      FakeRead(ForMatchGuard, _5);
+//      FakeRead(ForGuardBinding, _7);
 //      StorageLive(_6);
 //      _6 = ((_2 as Some).0: i32);
 //      _1 = const 1i32;
@@ -245,12 +245,12 @@ fn main() {
 //  }
 //  bb11: { // end of guard2
 //      StorageDead(_13);
-//      FakeRead(ForMatchGuard, _5);
-//      FakeRead(ForGuardBinding, _11);
 //      switchInt(move _12) -> [false: bb13, otherwise: bb12];
 //  }
 //  bb12: { // binding4 & arm4
 //      StorageDead(_12);
+//      FakeRead(ForMatchGuard, _5);
+//      FakeRead(ForGuardBinding, _11);
 //      StorageLive(_10);
 //      _10 = ((_2 as Some).0: i32);
 //      _1 = const 3i32;

src/test/mir-opt/match_test.rs

@@ -54,11 +54,11 @@ fn main() {
 //        _8 = &shallow _1;
 //        StorageLive(_9);
 //        _9 = _2;
-//        FakeRead(ForMatchGuard, _8);
 //        switchInt(move _9) -> [false: bb11, otherwise: bb10];
 //    }
 //    bb10: {
 //        StorageDead(_9);
+//        FakeRead(ForMatchGuard, _8);
 //        _3 = const 0i32;
 //        goto -> bb14;
 //    }
@@ -75,6 +75,7 @@ fn main() {
 //        goto -> bb14;
 //    }
 //    bb14: {
+//        StorageDead(_3);
 //        _0 = ();
 //        StorageDead(_2);
 //        StorageDead(_1);

src/test/mir-opt/nll/region-subtyping-basic.rs

@@ -22,9 +22,9 @@ fn main() {
 
 // END RUST SOURCE
 // START rustc.main.nll.0.mir
-// | '_#2r | U0 | {bb2[0..=8], bb3[0], bb5[0..=1]}
-// | '_#3r | U0 | {bb2[1..=8], bb3[0], bb5[0..=1]}
-// | '_#4r | U0 | {bb2[4..=8], bb3[0], bb5[0..=1]}
+// | '_#2r | U0 | {bb2[0..=8], bb3[0], bb5[0..=2]}
+// | '_#3r | U0 | {bb2[1..=8], bb3[0], bb5[0..=2]}
+// | '_#4r | U0 | {bb2[4..=8], bb3[0], bb5[0..=2]}
 // END rustc.main.nll.0.mir
 // START rustc.main.nll.0.mir
 // let _2: &'_#3r usize;

src/test/mir-opt/remove_fake_borrows.rs

@@ -38,14 +38,14 @@ fn main() {
 //     _7 = &shallow (*(*((_1 as Some).0: &'<empty> &'<empty> i32)));
 //     StorageLive(_8);
 //     _8 = _2;
-//     FakeRead(ForMatchGuard, _4);
-//     FakeRead(ForMatchGuard, _5);
-//     FakeRead(ForMatchGuard, _6);
-//     FakeRead(ForMatchGuard, _7);
 //     switchInt(move _8) -> [false: bb6, otherwise: bb5];
 // }
 // bb5: {
 //     StorageDead(_8);
+//     FakeRead(ForMatchGuard, _4);
+//     FakeRead(ForMatchGuard, _5);
+//     FakeRead(ForMatchGuard, _6);
+//     FakeRead(ForMatchGuard, _7);
 //     _0 = const 0i32;
 //     goto -> bb7;
 // }
@@ -84,14 +84,14 @@ fn main() {
 //     nop;
 //     StorageLive(_8);
 //     _8 = _2;
-//     nop;
-//     nop;
-//     nop;
-//     nop;
 //     switchInt(move _8) -> [false: bb6, otherwise: bb5];
 // }
 // bb5: {
 //     StorageDead(_8);
+//     nop;
+//     nop;
+//     nop;
+//     nop;
 //     _0 = const 0i32;
 //     goto -> bb7;
 // }

src/test/mir-opt/storage_ranges.rs

@@ -12,6 +12,7 @@ fn main() {
 //         StorageLive(_1);
 //         _1 = const 0i32;
 //         FakeRead(ForLet, _1);
+//         StorageLive(_2);
 //         StorageLive(_3);
 //         StorageLive(_4);
 //         StorageLive(_5);
@@ -23,6 +24,7 @@ fn main() {
 //         _2 = ();
 //         StorageDead(_4);
 //         StorageDead(_3);
+//         StorageDead(_2);
 //         StorageLive(_6);
 //         _6 = const 1i32;
 //         FakeRead(ForLet, _6);

src/test/mir-opt/while-storage.rs

@@ -0,0 +1,59 @@
+// Test that we correctly generate StorageDead statements for while loop
+// conditions on all branches
+
+fn get_bool(c: bool) -> bool {
+    c
+}
+
+fn while_loop(c: bool) {
+    while get_bool(c) {
+        if get_bool(c) {
+            break;
+        }
+    }
+}
+
+fn main() {
+    while_loop(false);
+}
+
+// END RUST SOURCE
+
+// START rustc.while_loop.PreCodegen.after.mir
+// bb0: {
+//     StorageLive(_2);
+//     StorageLive(_3);
+//     _3 = _1;
+//     _2 = const get_bool(move _3) -> bb2;
+// }
+// bb1: {
+//     return;
+// }
+// bb2: {
+//     StorageDead(_3);
+//     switchInt(move _2) -> [false: bb4, otherwise: bb3];
+// }
+// bb3: {
+//     StorageDead(_2);
+//     StorageLive(_4);
+//     StorageLive(_5);
+//     _5 = _1;
+//     _4 = const get_bool(move _5) -> bb5;
+// }
+// bb4: {
+//     StorageDead(_2);
+//     goto -> bb1;
+// }
+// bb5: {
+//     StorageDead(_5);
+//     switchInt(_4) -> [false: bb6, otherwise: bb7];
+// }
+// bb6: {
+//     StorageDead(_4);
+//     goto -> bb0;
+// }
+// bb7: {
+//     StorageDead(_4);
+//     goto -> bb1;
+// }
+// END rustc.while_loop.PreCodegen.after.mir

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 {};
+}