diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs index 19019e3ef744a..49ded10ba1fed 100644 --- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs +++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs @@ -122,7 +122,10 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> { ) { match rvalue { Rvalue::Aggregate(kind, operands) => { - state.flood_with(target.as_ref(), self.map(), FlatSet::Bottom); + // If we assign `target = Enum::Variant#0(operand)`, + // we must make sure that all `target as Variant#i` are `Top`. + state.flood(target.as_ref(), self.map()); + if let Some(target_idx) = self.map().find(target.as_ref()) { let (variant_target, variant_index) = match **kind { AggregateKind::Tuple | AggregateKind::Closure(..) => { @@ -131,18 +134,21 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> { AggregateKind::Adt(def_id, variant_index, ..) => { match self.tcx.def_kind(def_id) { DefKind::Struct => (Some(target_idx), None), - DefKind::Enum => (Some(target_idx), Some(variant_index)), + DefKind::Enum => ( + self.map.apply(target_idx, TrackElem::Variant(variant_index)), + Some(variant_index), + ), _ => (None, None), } } _ => (None, None), }; - if let Some(target) = variant_target { + if let Some(variant_target_idx) = variant_target { for (field_index, operand) in operands.iter().enumerate() { - if let Some(field) = self - .map() - .apply(target, TrackElem::Field(Field::from_usize(field_index))) - { + if let Some(field) = self.map().apply( + variant_target_idx, + TrackElem::Field(Field::from_usize(field_index)), + ) { let result = self.handle_operand(operand, state); state.insert_idx(field, result, self.map()); } @@ -151,6 +157,11 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> { if let Some(variant_index) = variant_index && let Some(discr_idx) = self.map().apply(target_idx, TrackElem::Discriminant) { + // We are assigning the discriminant as part of an aggregate. + // This discriminant can only alias a variant field's value if the operand + // had an invalid value for that type. + // Using invalid values is UB, so we are allowed to perform the assignment + // without extra flooding. let enum_ty = target.ty(self.local_decls, self.tcx).ty; if let Some(discr_val) = self.eval_discriminant(enum_ty, variant_index) { state.insert_value_idx(discr_idx, FlatSet::Elem(discr_val), &self.map); diff --git a/tests/mir-opt/dataflow-const-prop/enum.multiple.DataflowConstProp.diff b/tests/mir-opt/dataflow-const-prop/enum.multiple.DataflowConstProp.diff new file mode 100644 index 0000000000000..c4002d65e5db5 --- /dev/null +++ b/tests/mir-opt/dataflow-const-prop/enum.multiple.DataflowConstProp.diff @@ -0,0 +1,82 @@ +- // MIR for `multiple` before DataflowConstProp ++ // MIR for `multiple` after DataflowConstProp + + fn multiple(_1: bool, _2: u8) -> () { + debug x => _1; // in scope 0 at $DIR/enum.rs:+0:13: +0:14 + debug i => _2; // in scope 0 at $DIR/enum.rs:+0:22: +0:23 + let mut _0: (); // return place in scope 0 at $DIR/enum.rs:+0:29: +0:29 + let _3: std::option::Option; // in scope 0 at $DIR/enum.rs:+1:9: +1:10 + let mut _4: bool; // in scope 0 at $DIR/enum.rs:+1:16: +1:17 + let mut _5: u8; // in scope 0 at $DIR/enum.rs:+2:14: +2:15 + let mut _7: isize; // in scope 0 at $DIR/enum.rs:+9:23: +9:30 + scope 1 { + debug e => _3; // in scope 1 at $DIR/enum.rs:+1:9: +1:10 + let _6: u8; // in scope 1 at $DIR/enum.rs:+9:9: +9:10 + let _8: u8; // in scope 1 at $DIR/enum.rs:+9:28: +9:29 + scope 2 { + debug x => _6; // in scope 2 at $DIR/enum.rs:+9:9: +9:10 + let _9: u8; // in scope 2 at $DIR/enum.rs:+11:9: +11:10 + scope 4 { + debug y => _9; // in scope 4 at $DIR/enum.rs:+11:9: +11:10 + } + } + scope 3 { + debug i => _8; // in scope 3 at $DIR/enum.rs:+9:28: +9:29 + } + } + + bb0: { + StorageLive(_3); // scope 0 at $DIR/enum.rs:+1:9: +1:10 + StorageLive(_4); // scope 0 at $DIR/enum.rs:+1:16: +1:17 + _4 = _1; // scope 0 at $DIR/enum.rs:+1:16: +1:17 + switchInt(move _4) -> [0: bb2, otherwise: bb1]; // scope 0 at $DIR/enum.rs:+1:16: +1:17 + } + + bb1: { + StorageLive(_5); // scope 0 at $DIR/enum.rs:+2:14: +2:15 + _5 = _2; // scope 0 at $DIR/enum.rs:+2:14: +2:15 + _3 = Option::::Some(move _5); // scope 0 at $DIR/enum.rs:+2:9: +2:16 + StorageDead(_5); // scope 0 at $DIR/enum.rs:+2:15: +2:16 + goto -> bb3; // scope 0 at $DIR/enum.rs:+1:13: +5:6 + } + + bb2: { + _3 = Option::::None; // scope 0 at $DIR/enum.rs:+4:9: +4:13 + goto -> bb3; // scope 0 at $DIR/enum.rs:+1:13: +5:6 + } + + bb3: { + StorageDead(_4); // scope 0 at $DIR/enum.rs:+5:5: +5:6 + StorageLive(_6); // scope 1 at $DIR/enum.rs:+9:9: +9:10 + _7 = discriminant(_3); // scope 1 at $DIR/enum.rs:+9:19: +9:20 + switchInt(move _7) -> [0: bb4, 1: bb6, otherwise: bb5]; // scope 1 at $DIR/enum.rs:+9:13: +9:20 + } + + bb4: { + _6 = const 0_u8; // scope 1 at $DIR/enum.rs:+9:45: +9:46 + goto -> bb7; // scope 1 at $DIR/enum.rs:+9:45: +9:46 + } + + bb5: { + unreachable; // scope 1 at $DIR/enum.rs:+9:19: +9:20 + } + + bb6: { + StorageLive(_8); // scope 1 at $DIR/enum.rs:+9:28: +9:29 + _8 = ((_3 as Some).0: u8); // scope 1 at $DIR/enum.rs:+9:28: +9:29 + _6 = _8; // scope 3 at $DIR/enum.rs:+9:34: +9:35 + StorageDead(_8); // scope 1 at $DIR/enum.rs:+9:34: +9:35 + goto -> bb7; // scope 1 at $DIR/enum.rs:+9:34: +9:35 + } + + bb7: { + StorageLive(_9); // scope 2 at $DIR/enum.rs:+11:9: +11:10 + _9 = _6; // scope 2 at $DIR/enum.rs:+11:13: +11:14 + _0 = const (); // scope 0 at $DIR/enum.rs:+0:29: +12:2 + StorageDead(_9); // scope 2 at $DIR/enum.rs:+12:1: +12:2 + StorageDead(_6); // scope 1 at $DIR/enum.rs:+12:1: +12:2 + StorageDead(_3); // scope 0 at $DIR/enum.rs:+12:1: +12:2 + return; // scope 0 at $DIR/enum.rs:+12:2: +12:2 + } + } + diff --git a/tests/mir-opt/dataflow-const-prop/enum.rs b/tests/mir-opt/dataflow-const-prop/enum.rs index 7ea405bd9c408..79a20d7ef457d 100644 --- a/tests/mir-opt/dataflow-const-prop/enum.rs +++ b/tests/mir-opt/dataflow-const-prop/enum.rs @@ -46,7 +46,23 @@ fn mutate_discriminant() -> u8 { ) } +// EMIT_MIR enum.multiple.DataflowConstProp.diff +fn multiple(x: bool, i: u8) { + let e = if x { + Some(i) + } else { + None + }; + // The dataflow state must have: + // discriminant(e) => Top + // (e as Some).0 => Top + let x = match e { Some(i) => i, None => 0 }; + // Therefore, `x` should be `Top` here, and no replacement shall happen. + let y = x; +} + fn main() { simple(); mutate_discriminant(); + multiple(false, 5); } diff --git a/tests/mir-opt/dataflow-const-prop/enum.simple.DataflowConstProp.diff b/tests/mir-opt/dataflow-const-prop/enum.simple.DataflowConstProp.diff index 1fb65e6584525..22bdc35d694c1 100644 --- a/tests/mir-opt/dataflow-const-prop/enum.simple.DataflowConstProp.diff +++ b/tests/mir-opt/dataflow-const-prop/enum.simple.DataflowConstProp.diff @@ -45,8 +45,10 @@ bb3: { StorageLive(_4); // scope 1 at $DIR/enum.rs:+2:29: +2:30 - _4 = ((_1 as V1).0: i32); // scope 1 at $DIR/enum.rs:+2:29: +2:30 - _2 = _4; // scope 3 at $DIR/enum.rs:+2:35: +2:36 +- _4 = ((_1 as V1).0: i32); // scope 1 at $DIR/enum.rs:+2:29: +2:30 +- _2 = _4; // scope 3 at $DIR/enum.rs:+2:35: +2:36 ++ _4 = const 0_i32; // scope 1 at $DIR/enum.rs:+2:29: +2:30 ++ _2 = const 0_i32; // scope 3 at $DIR/enum.rs:+2:35: +2:36 StorageDead(_4); // scope 1 at $DIR/enum.rs:+2:35: +2:36 goto -> bb4; // scope 1 at $DIR/enum.rs:+2:35: +2:36 }