Move generator check earlier in inlining.

Author: cjgillot

compiler/rustc_mir_transform/src/inline.rs

@@ -68,6 +68,12 @@ 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 body.generator.is_some() {
+        return false;
+    }
 
     let mut this = Inliner {
         tcx,
@@ -202,14 +208,6 @@ impl<'tcx> Inliner<'tcx> {
 
         if let Some(callee_def_id) = callee.def_id().as_local() {
             let callee_hir_id = self.tcx.hir().local_def_id_to_hir_id(callee_def_id);
-            // 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 caller_body.generator.is_some() {
-                return Err("local generator (query cycle avoidance)");
-            }
-
             // Avoid a cycle here by only using `instance_mir` only if we have
             // a lower `HirId` than the callee. This ensures that the callee will
             // not inline us. This trick only works without incremental compilation.

src/test/mir-opt/generator_drop_cleanup.main-{closure#0}.generator_drop.0.mir

@@ -20,21 +20,16 @@ fn main::{closure#0}(_1: *mut [generator@$DIR/generator-drop-cleanup.rs:10:15: 1
     let _3: std::string::String;         // in scope 0 at $DIR/generator-drop-cleanup.rs:11:13: 11:15
     let _4: ();                          // in scope 0 at $DIR/generator-drop-cleanup.rs:12:9: 12:14
     let mut _5: ();                      // in scope 0 at $DIR/generator-drop-cleanup.rs:12:9: 12:14
-    let mut _7: ();                      // in scope 0 at $DIR/generator-drop-cleanup.rs:10:18: 10:18
-    let mut _8: ();                      // in scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
-    let mut _9: u32;                     // in scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
+    let mut _6: ();                      // in scope 0 at $DIR/generator-drop-cleanup.rs:10:18: 10:18
+    let mut _7: ();                      // in scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
+    let mut _8: u32;                     // in scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
     scope 1 {
         debug _s => (((*_1) as variant#3).0: std::string::String); // in scope 1 at $DIR/generator-drop-cleanup.rs:11:13: 11:15
     }
-    scope 2 (inlined String::new) {      // at $DIR/generator-drop-cleanup.rs:11:18: 11:31
-        let mut _6: std::vec::Vec<u8>;   // in scope 2 at $DIR/generator-drop-cleanup.rs:11:18: 11:31
-        scope 3 (inlined Vec::<u8>::new) { // at $DIR/generator-drop-cleanup.rs:11:18: 11:31
-        }
-    }
 
     bb0: {
-        _9 = discriminant((*_1));        // scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
-        switchInt(move _9) -> [0_u32: bb7, 3_u32: bb10, otherwise: bb11]; // scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
+        _8 = discriminant((*_1));        // scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
+        switchInt(move _8) -> [0_u32: bb7, 3_u32: bb10, otherwise: bb11]; // scope 0 at $DIR/generator-drop-cleanup.rs:10:15: 13:6
     }
 
     bb1: {

src/test/ui/mir/remove-zsts-query-cycle.rs

@@ -2,7 +2,7 @@
 //   optimized mir -> remove zsts -> layout of a generator -> optimized mir.
 //
 // edition:2018
-// compile-flags: --crate-type=lib
+// compile-flags: --crate-type=lib -Zinline-mir=yes
 // build-pass
 
 pub async fn listen() -> Result<(), std::io::Error> {