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Remove the IsPeriodSelf function, use constant value comparison instead (#5731)

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The `IsPeriodSelf` function is problematic, as it's possible for a
FacetType to contain multiple `.Self` bindings which refer to different
selves, when one FacetType is nested within another: `I where .Self.J =
(K where .Self impls type)`.

The `WhereExpr` instruction contains the instruction of the `.Self` of
that `where` clause, which is what `IsPeriodSelf` is looking for, so we
can compare with its constant value instead.
This commit is contained in:
Dana Jansens
2025-06-25 20:05:49 +00:00
committed by GitHub
parent 72cd8717e3
commit 1d2cf1ddcb
1 changed files with 12 additions and 27 deletions
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toolchain/check/eval.cpp
+12 -27
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@@ -1999,32 +1999,17 @@ auto TryEvalTypedInst<SemIR::BindSymbolicName>(EvalContext& eval_context,
return MakeConstantResult(eval_context.context(), bind, phase);
}
static auto IsPeriodSelf(EvalContext& eval_context, SemIR::ConstantId const_id)
-> bool {
// This also rejects the singleton Error value as it's concrete.
if (!const_id.is_symbolic()) {
return false;
// Returns whether `inst_id` is the same constant facet value as
// `facet_value_inst_id`.
static auto IsSameFacetValue(Context& context, SemIR::InstId inst_id,
SemIR::InstId facet_value_inst_id) -> bool {
auto const_id = context.constant_values().Get(inst_id);
if (auto facet_access_type = context.insts().TryGetAs<SemIR::FacetAccessType>(
context.constant_values().GetInstId(const_id))) {
const_id =
context.constant_values().Get(facet_access_type->facet_value_inst_id);
}
const auto& symbolic =
eval_context.constant_values().GetSymbolicConstant(const_id);
// Fast early reject before doing more expensive operations.
if (symbolic.dependence != SemIR::ConstantDependence::PeriodSelf) {
return false;
}
auto inst_id = symbolic.inst_id;
// Unwrap the `FacetAccessType` instruction, which we get when the `.Self` is
// converted to `type`.
if (auto facet_access_type =
eval_context.insts().TryGetAs<SemIR::FacetAccessType>(inst_id)) {
inst_id = facet_access_type->facet_value_inst_id;
}
if (auto bind_symbolic_name =
eval_context.insts().TryGetAs<SemIR::BindSymbolicName>(inst_id)) {
const auto& bind_name =
eval_context.entity_names().Get(bind_symbolic_name->entity_name_id);
return bind_name.name_id == SemIR::NameId::PeriodSelf;
}
return false;
return const_id == context.constant_values().Get(facet_value_inst_id);
}
// TODO: Convert this to an EvalConstantInst function. This will require
@@ -2066,8 +2051,8 @@ auto TryEvalTypedInst<SemIR::WhereExpr>(EvalContext& eval_context,
} else if (auto impls =
eval_context.insts().TryGetAs<SemIR::RequirementImpls>(
inst_id)) {
if (IsPeriodSelf(eval_context,
eval_context.constant_values().Get(impls->lhs_id))) {
if (IsSameFacetValue(eval_context.context(), impls->lhs_id,
typed_inst.period_self_id)) {
if (impls->rhs_id == SemIR::TypeType::TypeInstId) {
// `.Self impls type` -> nothing to do.
} else if (auto facet_type =