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Encode constant determinism in disambiguator.

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This commit is contained in:
Camille GILLOT 2024-06-26 13:27:38 +00:00
parent 9d23c86176
commit 61ef0441b8
1 changed files with 8 additions and 7 deletions
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15
compiler/rustc_mir_transform/src/gvn.rs
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@ -204,6 +204,7 @@ enum Value<'tcx> {
value: Const<'tcx>,
/// Some constants do not have a deterministic value. To avoid merging two instances of the
/// same `Const`, we assign them an additional integer index.
// `disambiguator` is 0 iff the constant is deterministic.
disambiguator: usize,
},
/// An aggregate value, either tuple/closure/struct/enum.
@ -288,7 +289,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
rev_locals: IndexVec::with_capacity(num_values),
values: FxIndexSet::with_capacity_and_hasher(num_values, Default::default()),
evaluated: IndexVec::with_capacity(num_values),
next_opaque: Some(0),
next_opaque: Some(1),
feature_unsized_locals: tcx.features().unsized_locals,
ssa,
dominators,
@ -360,6 +361,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
let next_opaque = self.next_opaque.as_mut()?;
let disambiguator = *next_opaque;
*next_opaque += 1;
assert_ne!(disambiguator, 0);
disambiguator
};
Some(self.insert(Value::Constant { value, disambiguator }))
@ -1447,12 +1449,11 @@ impl<'tcx> VnState<'_, 'tcx> {
/// If `index` is a `Value::Constant`, return the `Constant` to be put in the MIR.
fn try_as_constant(&mut self, index: VnIndex) -> Option<ConstOperand<'tcx>> {
// This was already constant in MIR, do not change it.
if let Value::Constant { value, disambiguator: _ } = *self.get(index)
// If the constant is not deterministic, adding an additional mention of it in MIR will
// not give the same value as the former mention.
&& value.is_deterministic()
{
// This was already constant in MIR, do not change it. If the constant is not
// deterministic, adding an additional mention of it in MIR will not give the same value as
// the former mention.
if let Value::Constant { value, disambiguator: 0 } = *self.get(index) {
assert!(value.is_deterministic());
return Some(ConstOperand { span: DUMMY_SP, user_ty: None, const_: value });
}