Generator drop glue jumps from is_cleanup:false -> is_cleanup:true and the other way

[bjorn3]

#![feature(generators, generator_trait)]

fn main() {
    let mut foo = || {
        yield;
    };
}

I only tested this with -Cpanic=abort.

Wrong jumps: bb1 -> bb5, bb4 -> bb6, bb5 -> bb2.

Note: made mir dump below using println!("{:#?}"), because rustc_mir::util::write_mir_pretty doesn't work correctly for shims.

Mir for `Instance { def: DropGlue(DefId(2/0:691 ~ core[479c]::ptr[0]::real_drop_in_place[0]), Some([generator@/Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6 {()}])), substs: [[generator@/Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6 {()}]] } _ZN4core3ptr18real_drop_in_place17h0fdaf8ce1f626024E`

Mir {
    basic_blocks: [
        BasicBlockData {
            statements: [],
            terminator: Some(
                Terminator {
                    source_info: SourceInfo {
                        span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
                        scope: scope[0]
                    },
                    kind: switchInt(((*_1).0: u32)) -> [0u32: bb4, 3u32: bb7, otherwise: bb8]
                }
            ),
            is_cleanup: false
        },
        BasicBlockData {
            statements: [],
            terminator: Some(
                Terminator {
                    source_info: SourceInfo {
                        span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:10:5: 10:6,
                        scope: scope[0]
                    },
                    kind: goto -> bb5
                }
            ),
            is_cleanup: false
        },
        BasicBlockData {
            statements: [],
            terminator: Some(
                Terminator {
                    source_info: SourceInfo {
                        span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
                        scope: scope[0]
                    },
                    kind: return
                }
            ),
            is_cleanup: false
        },
        BasicBlockData {
            statements: [],
            terminator: Some(
                Terminator {
                    source_info: SourceInfo {
                        span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
                        scope: scope[0]
                    },
                    kind: return
                }
            ),
            is_cleanup: false
        },
        BasicBlockData {
            statements: [],
            terminator: Some(
                Terminator {
                    source_info: SourceInfo {
                        span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
                        scope: scope[0]
                    },
                    kind: goto -> bb6
                }
            ),
            is_cleanup: false
        },
        BasicBlockData {
            statements: [],
            terminator: Some(
                Terminator {
                    source_info: SourceInfo {
                        span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:10:5: 10:6,
                        scope: scope[0]
                    },
                    kind: goto -> bb2
                }
            ),
            is_cleanup: true
        },
        BasicBlockData {
            statements: [],
            terminator: Some(
                Terminator {
                    source_info: SourceInfo {
                        span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
                        scope: scope[0]
                    },
                    kind: goto -> bb3
                }
            ),
            is_cleanup: true
        },
        BasicBlockData {
            statements: [
                StorageLive(_3)
            ],
            terminator: Some(
                Terminator {
                    source_info: SourceInfo {
                        span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
                        scope: scope[0]
                    },
                    kind: goto -> bb1
                }
            ),
            is_cleanup: false
        },
        BasicBlockData {
            statements: [],
            terminator: Some(
                Terminator {
                    source_info: SourceInfo {
                        span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
                        scope: scope[0]
                    },
                    kind: return
                }
            ),
            is_cleanup: false
        }
    ],
    phase: Validated,
    source_scopes: [
        SourceScopeData {
            span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
            parent_scope: None
        }
    ],
    source_scope_local_data: Set(
        [
            SourceScopeLocalData {
                lint_root: HirId {
                    owner: DefIndex(0:3),
                    local_id: 8
                },
                safety: Safe
            }
        ]
    ),
    promoted: [],
    yield_ty: None,
    generator_drop: None,
    generator_layout: Some(
        GeneratorLayout {
            fields: []
        }
    ),
    local_decls: [
        LocalDecl {
            mutability: Mut,
            is_user_variable: None,
            internal: false,
            is_block_tail: None,
            ty: (),
            user_ty: UserTypeProjections {
                contents: []
            },
            name: None,
            source_info: SourceInfo {
                span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
                scope: scope[0]
            },
            visibility_scope: scope[0]
        },
        LocalDecl {
            mutability: Mut,
            is_user_variable: None,
            internal: false,
            is_block_tail: None,
            ty: *mut [generator@/Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6 {()}],
            user_ty: UserTypeProjections {
                contents: []
            },
            name: None,
            source_info: SourceInfo {
                span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
                scope: scope[0]
            },
            visibility_scope: scope[0]
        },
        LocalDecl {
            mutability: Mut,
            is_user_variable: None,
            internal: false,
            is_block_tail: None,
            ty: (),
            user_ty: UserTypeProjections {
                contents: []
            },
            name: None,
            source_info: SourceInfo {
                span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:9:9: 9:14,
                scope: scope[0]
            },
            visibility_scope: scope[0]
        },
        LocalDecl {
            mutability: Mut,
            is_user_variable: None,
            internal: false,
            is_block_tail: None,
            ty: (),
            user_ty: UserTypeProjections {
                contents: []
            },
            name: None,
            source_info: SourceInfo {
                span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:9:9: 9:14,
                scope: scope[0]
            },
            visibility_scope: scope[0]
        },
        LocalDecl {
            mutability: Mut,
            is_user_variable: None,
            internal: false,
            is_block_tail: None,
            ty: (),
            user_ty: UserTypeProjections {
                contents: []
            },
            name: None,
            source_info: SourceInfo {
                span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:22: 8:22,
                scope: scope[0]
            },
            visibility_scope: scope[0]
        }
    ],
    user_type_annotations: [],
    arg_count: 1,
    upvar_decls: [],
    spread_arg: None,
    control_flow_destroyed: [],
    span: /Users/bjorn/Documents/rustc_codegen_cranelift/rust/src/test/run-pass/generator/panic-drops.rs:8:19: 10:6,
    cache: Cache {
        predecessors: RwLock(
            RefCell {
                value: None
            }
        )
    }
}

[bjorn3]

I noticed this, because cg_clif crashed with a verifier error about a jump to an undefined bb. (cg_clif omits is_cleanup blocks because it doesn't support unwinding yet anyway)

[matthewjasper]

Pretty printed shim (not fully transformed)

// MIR for `main::{{closure}}`
// source = MirSource { instance: Item(DefId(0/1:9 ~ generator_drop_shim[317d]::main[0]::{{closure}}[0])), promoted: None }
// pass_name = generator_drop
// disambiguator = 0
// generator_layout = GeneratorLayout { fields: [] }

fn main::{{closure}}(_1: *mut [generator@src/generator-drop-shim.rs:4:19: 6:6 {()}]) -> () {
    let mut _0: ();                      // return place
    let mut _2: ();
    let mut _3: ();
    let mut _4: ();

    bb0: {                              
        switchInt(((*_1).0: u32)) -> [0u32: bb4, 3u32: bb7, otherwise: bb8]; // bb0[0]: scope 0 at src/generator-drop-shim.rs:4:19: 6:6
    }

    bb1: {                              
        goto -> bb5;                     // bb1[0]: scope 0 at src/generator-drop-shim.rs:6:5: 6:6
    }

    bb2: {                              
        return;                          // bb2[0]: scope 0 at src/generator-drop-shim.rs:4:19: 6:6
    }

    bb3: {                              
        return;                          // bb3[0]: scope 0 at src/generator-drop-shim.rs:4:19: 6:6
    }

    bb4: {                              
        goto -> bb6;                     // bb4[0]: scope 0 at src/generator-drop-shim.rs:4:19: 6:6
    }

    bb5: {                              
        goto -> bb2;                     // bb5[0]: scope 0 at src/generator-drop-shim.rs:6:5: 6:6
    }

    bb6: {                               // cleanup
        goto -> bb3;                     // bb6[0]: scope 0 at src/generator-drop-shim.rs:4:19: 6:6
    }

    bb7: {                              
        StorageLive(_3);                 // bb7[0]: scope 0 at src/generator-drop-shim.rs:4:19: 6:6
        goto -> bb1;                     // bb7[1]: scope 0 at src/generator-drop-shim.rs:4:19: 6:6
    }

    bb8: {                              
        return;                          // bb8[0]: scope 0 at src/generator-drop-shim.rs:4:19: 6:6
    }
}

[bjorn3]

Forgot -Zdump-mir existed :)