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Rollup merge of #108208 - cjgillot:flood-enum, r=oli-obk

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Correctly handle aggregates in DataflowConstProp

The previous implementation from https://github.com/rust-lang/rust/pull/107411 flooded target of an aggregate assignment with `Bottom`, corresponding to the `deinit` that the interpreter does.

As a consequence, when assigning `target = Enum::Variant#i(...)` all the `(target as Variant#j)` were at `Bottom` while they should have been `Top`.

This PR replaces that flooding with `Top`.

Aside, it corrects a second bug where the wrong place would be used to assign to enum variant fields, resulting to nothing happening.

Fixes https://github.com/rust-lang/rust/issues/108166
This commit is contained in:
Matthias Krüger 2023-02-23 06:18:06 +01:00 committed by GitHub
commit a423fa7b46
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4 changed files with 120 additions and 9 deletions
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25
compiler/rustc_mir_transform/src/dataflow_const_prop.rs
View File

@ -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);

82
tests/mir-opt/dataflow-const-prop/enum.multiple.DataflowConstProp.diff Normal file
View File

@ -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
tests/mir-opt/dataflow-const-prop/enum.rs
View File

@ -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
tests/mir-opt/dataflow-const-prop/enum.simple.DataflowConstProp.diff
View File

@ -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
}