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Correctly handle aggregates in DataflowConstProp #108208

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Merged
merged 3 commits into from
Feb 23, 2023
Merged

Correctly handle aggregates in DataflowConstProp #108208

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6506837
Add mir-opt test.
cjgillot Feb 18, 2023
7213eaa
Flood aggregate assignments with `Top`.
cjgillot Feb 18, 2023
efb4688
Use the correct place for enum variants.
cjgillot Feb 18, 2023
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25 changes: 18 additions & 7 deletions compiler/rustc_mir_transform/src/dataflow_const_prop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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(..) => {
Expand All @@ -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());
}
Expand All @@ -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);
Expand Down
82 changes: 82 additions & 0 deletions tests/mir-opt/dataflow-const-prop/enum.multiple.DataflowConstProp.diff
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Original file line number Diff line number Diff line change
@@ -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<u8>; // 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::<u8>::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::<u8>::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
}
}

16 changes: 16 additions & 0 deletions tests/mir-opt/dataflow-const-prop/enum.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
}
6 changes: 4 additions & 2 deletions tests/mir-opt/dataflow-const-prop/enum.simple.DataflowConstProp.diff
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Original file line number Diff line number Diff line change
Expand Up @@ -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
}
Expand Down