Enable MIR inlining on generators.

Author: cjgillot

compiler/rustc_mir_transform/src/inline.rs

@@ -79,12 +79,6 @@ fn inline<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
     if body.source.promoted.is_some() {
         return false;
     }
-    // Avoid inlining into generators, since their `optimized_mir` is used for layout computation,
-    // which can create a cycle, even when no attempt is made to inline the function in the other
-    // direction.
-    if tcx.generator_kind(def_id).is_some() {
-        return false;
-    }
 
     let param_env = tcx.param_env_reveal_all_normalized(def_id);
 

src/test/mir-opt/inline/inline-async.rs

@@ -1,5 +1,4 @@
 // Checks that inliner doesn't introduce cycles when optimizing generators.
-// The outcome of optimization is not verfied, just the absence of the cycle.
 // Regression test for #76181.
 //
 // edition:2018
@@ -8,11 +7,13 @@
 
 pub struct S;
 
-impl S {
-    pub async fn g(&mut self) {
-        self.h();
-    }
-    pub fn h(&mut self) {
-        let _ = self.g();
-    }
+// EMIT_MIR inline_async.g.Inline.diff
+pub async fn g(s: &mut S) {
+    h(s);
+}
+
+// EMIT_MIR inline_async.h.Inline.diff
+#[inline(always)]
+pub fn h(s: &mut S) {
+    let _ = g(s);
 }

src/test/mir-opt/inline/inline_async.g.Inline.diff

@@ -0,0 +1,34 @@
+- // MIR for `g` before Inline
++ // MIR for `g` after Inline
+  
+  fn g(_1: &mut S) -> std::future::from_generator::GenFuture<[static generator@$DIR/inline-async.rs:11:27: 13:2]> {
+      debug s => _1;                       // in scope 0 at $DIR/inline-async.rs:+0:16: +0:17
+      let mut _0: std::future::from_generator::GenFuture<[static generator@$DIR/inline-async.rs:11:27: 13:2]>; // return place in scope 0 at $DIR/inline-async.rs:+0:27: +0:27
+      let mut _2: [static generator@$DIR/inline-async.rs:11:27: 13:2]; // in scope 0 at $DIR/inline-async.rs:+0:27: +2:2
++     scope 1 (inlined std::future::from_generator::<[static generator@$DIR/inline-async.rs:11:27: 13:2]>) { // at $DIR/inline-async.rs:11:27: 13:2
++         debug gen => _2;                 // in scope 1 at $SRC_DIR/core/src/future/mod.rs:LL:COL
++         let mut _3: [static generator@$DIR/inline-async.rs:11:27: 13:2]; // in scope 1 at $SRC_DIR/core/src/future/mod.rs:LL:COL
++     }
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/inline-async.rs:+0:27: +2:2
+          Deinit(_2);                      // scope 0 at $DIR/inline-async.rs:+0:27: +2:2
+          (_2.0: &mut S) = move _1;        // scope 0 at $DIR/inline-async.rs:+0:27: +2:2
+          discriminant(_2) = 0;            // scope 0 at $DIR/inline-async.rs:+0:27: +2:2
+-         _0 = std::future::from_generator::<[static generator@$DIR/inline-async.rs:11:27: 13:2]>(move _2) -> bb1; // scope 0 at $DIR/inline-async.rs:+0:27: +2:2
+-                                          // mir::Constant
+-                                          // + span: $DIR/inline-async.rs:11:27: 13:2
+-                                          // + literal: Const { ty: fn([static generator@$DIR/inline-async.rs:11:27: 13:2]) -> impl Future<Output = ()> {std::future::from_generator::<[static generator@$DIR/inline-async.rs:11:27: 13:2]>}, val: Value(<ZST>) }
+-     }
+- 
+-     bb1: {
++         StorageLive(_3);                 // scope 1 at $SRC_DIR/core/src/future/mod.rs:LL:COL
++         _3 = move _2;                    // scope 1 at $SRC_DIR/core/src/future/mod.rs:LL:COL
++         Deinit(_0);                      // scope 1 at $SRC_DIR/core/src/future/mod.rs:LL:COL
++         (_0.0: [static generator@$DIR/inline-async.rs:11:27: 13:2]) = move _3; // scope 1 at $SRC_DIR/core/src/future/mod.rs:LL:COL
++         StorageDead(_3);                 // scope 1 at $SRC_DIR/core/src/future/mod.rs:LL:COL
+          StorageDead(_2);                 // scope 0 at $DIR/inline-async.rs:+2:1: +2:2
+          return;                          // scope 0 at $DIR/inline-async.rs:+2:2: +2:2
+      }
+  }
+  

src/test/mir-opt/inline/inline_async.h.Inline.diff

@@ -0,0 +1,29 @@
+- // MIR for `h` before Inline
++ // MIR for `h` after Inline
+  
+  fn h(_1: &mut S) -> () {
+      debug s => _1;                       // in scope 0 at $DIR/inline-async.rs:+0:10: +0:11
+      let mut _0: ();                      // return place in scope 0 at $DIR/inline-async.rs:+0:21: +0:21
+      let mut _2: std::future::from_generator::GenFuture<[static generator@$DIR/inline-async.rs:11:27: 13:2]>; // in scope 0 at $DIR/inline-async.rs:+1:13: +1:17
+      let mut _3: &mut S;                  // in scope 0 at $DIR/inline-async.rs:+1:15: +1:16
+      scope 1 {
+      }
+  
+      bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/inline-async.rs:+1:13: +1:17
+          StorageLive(_3);                 // scope 0 at $DIR/inline-async.rs:+1:15: +1:16
+          _3 = &mut (*_1);                 // scope 0 at $DIR/inline-async.rs:+1:15: +1:16
+          _2 = g(move _3) -> bb1;          // scope 0 at $DIR/inline-async.rs:+1:13: +1:17
+                                           // mir::Constant
+                                           // + span: $DIR/inline-async.rs:18:13: 18:14
+                                           // + literal: Const { ty: for<'r> fn(&'r mut S) -> impl for<'r> Future<Output = ()> {g}, val: Value(<ZST>) }
+      }
+  
+      bb1: {
+          StorageDead(_3);                 // scope 0 at $DIR/inline-async.rs:+1:16: +1:17
+          StorageDead(_2);                 // scope 0 at $DIR/inline-async.rs:+1:17: +1:18
+          _0 = const ();                   // scope 0 at $DIR/inline-async.rs:+0:21: +2:2
+          return;                          // scope 0 at $DIR/inline-async.rs:+2:2: +2:2
+      }
+  }
+