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Facet types support rewrite (where .A =...) constraints (#4613)

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* Rewrite constraints are stored in a facet type, substituted, imported,
and formatted.
* We now distinguish `.Self` from other symbolic bindings in two ways:
* `.Self` itself now has an invalid compile time binding index (since it
doesn't bind to any of the generic parameters). As a result, we no
longer need to create a generic region in `handle_where.cpp`.
* There is a new phase tracking values that are only symbolic because
they transitively depend on `.Self`. This allows us to give the result
of a `where` expression template phase as long as it doesn't use any
symbolic constants other than `.Self` or other designators.
* `AddConstant` has been removed from `check/context` since it was only
used from `eval`. This meant less plumbing of the phase change.
* Evaluation of `BindSymbolicName` now also performs substitution into
its type.
* Include a bit more information in some diagnostics.
* `StringifyTypeExpr` outputs rewrites, which required adding support
for associated entities as well.
  * Associated entities now have an entity name set when importing.
* Adds tests for some interesting cases with rewrites and uses of
`.Self` mixed with other symbolic constants.

Still to do:
* There is no validation that any particular type satisfies rewrite
constraints.
  * Access to members of a facet type do not see the rewritten values.
* Impls don't recognize whether associated constants have rewrites
setting their values.
  * No support for resolving facet types.

---------

Co-authored-by: Josh L <josh11b@users.noreply.github.com>
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
This commit is contained in:
josh11b
2024-12-03 22:44:39 +00:00
committed by GitHub
co-authored by Josh L Richard Smith
parent dc5edb88fb
commit 33110d096c
44 changed files with 3113 additions and 1446 deletions
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/eval.cpp
+88 -24
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@@ -178,6 +178,9 @@ namespace {
enum class Phase : uint8_t {
// Value could be entirely and concretely computed.
Template,
// Evaluation phase is symbolic because the expression involves specifically a
// reference to `.Self`.
PeriodSelfSymbolic,
// Evaluation phase is symbolic because the expression involves a reference to
// a symbolic binding.
Symbolic,
@@ -191,16 +194,20 @@ enum class Phase : uint8_t {
} // namespace
// Gets the phase in which the value of a constant will become available.
static auto GetPhase(SemIR::ConstantId constant_id) -> Phase {
static auto GetPhase(EvalContext& eval_context, SemIR::ConstantId constant_id)
-> Phase {
if (!constant_id.is_constant()) {
return Phase::Runtime;
} else if (constant_id == SemIR::ConstantId::Error) {
return Phase::UnknownDueToError;
} else if (constant_id.is_template()) {
return Phase::Template;
} else if (eval_context.constant_values().DependsOnGenericParameter(
constant_id)) {
return Phase::Symbolic;
} else {
CARBON_CHECK(constant_id.is_symbolic());
return Phase::Symbolic;
return Phase::PeriodSelfSymbolic;
}
}
@@ -210,14 +217,34 @@ static auto LatestPhase(Phase a, Phase b) -> Phase {
std::max(static_cast<uint8_t>(a), static_cast<uint8_t>(b)));
}
// `where` expressions using `.Self` should not be considered symbolic
// - `Interface where .Self impls I and .A = bool` -> template
// - `T:! type` ... `Interface where .A = T` -> symbolic, since uses `T` which
// is symbolic and not due to `.Self`.
static auto UpdatePhaseIgnorePeriodSelf(EvalContext& eval_context,
SemIR::ConstantId constant_id,
Phase* phase) {
Phase constant_phase = GetPhase(eval_context, constant_id);
// Since LatestPhase(x, Phase::Template) == x, this is equivalent to replacing
// Phase::PeriodSelfSymbolic with Phase::Template.
if (constant_phase != Phase::PeriodSelfSymbolic) {
*phase = LatestPhase(*phase, constant_phase);
}
}
// Forms a `constant_id` describing a given evaluation result.
static auto MakeConstantResult(Context& context, SemIR::Inst inst, Phase phase)
-> SemIR::ConstantId {
switch (phase) {
case Phase::Template:
return context.AddConstant(inst, /*is_symbolic=*/false);
return context.constants().GetOrAdd(inst,
SemIR::ConstantStore::IsTemplate);
case Phase::PeriodSelfSymbolic:
return context.constants().GetOrAdd(
inst, SemIR::ConstantStore::IsPeriodSelfSymbolic);
case Phase::Symbolic:
return context.AddConstant(inst, /*is_symbolic=*/true);
return context.constants().GetOrAdd(inst,
SemIR::ConstantStore::IsSymbolic);
case Phase::UnknownDueToError:
return SemIR::ConstantId::Error;
case Phase::Runtime:
@@ -270,7 +297,7 @@ static auto MakeFloatResult(Context& context, SemIR::TypeId type_id,
static auto GetConstantValue(EvalContext& eval_context, SemIR::InstId inst_id,
Phase* phase) -> SemIR::InstId {
auto const_id = eval_context.GetConstantValue(inst_id);
*phase = LatestPhase(*phase, GetPhase(const_id));
*phase = LatestPhase(*phase, GetPhase(eval_context, const_id));
return eval_context.constant_values().GetInstId(const_id);
}
@@ -279,7 +306,7 @@ static auto GetConstantValue(EvalContext& eval_context, SemIR::InstId inst_id,
static auto GetConstantValue(EvalContext& eval_context, SemIR::TypeId type_id,
Phase* phase) -> SemIR::TypeId {
auto const_id = eval_context.GetConstantValue(type_id);
*phase = LatestPhase(*phase, GetPhase(const_id));
*phase = LatestPhase(*phase, GetPhase(eval_context, const_id));
return eval_context.context().GetTypeIdForTypeConstant(const_id);
}
@@ -395,7 +422,7 @@ static auto GetConstantValue(EvalContext& eval_context,
}
// Like `GetConstantValue` but does a `FacetTypeId` -> `FacetTypeInfo`
// conversion.
// conversion. Does not perform canonicalization.
static auto GetConstantFacetTypeInfo(EvalContext& eval_context,
SemIR::FacetTypeId facet_type_id,
Phase* phase) -> SemIR::FacetTypeInfo {
@@ -404,8 +431,14 @@ static auto GetConstantFacetTypeInfo(EvalContext& eval_context,
interface.specific_id =
GetConstantValue(eval_context, interface.specific_id, phase);
}
std::sort(info.impls_constraints.begin(), info.impls_constraints.end());
// TODO: Process & canonicalize other requirements.
for (auto& rewrite : info.rewrite_constraints) {
rewrite.lhs_const_id = eval_context.GetInContext(rewrite.lhs_const_id);
rewrite.rhs_const_id = eval_context.GetInContext(rewrite.rhs_const_id);
// `where` requirements using `.Self` should not be considered symbolic
UpdatePhaseIgnorePeriodSelf(eval_context, rewrite.lhs_const_id, phase);
UpdatePhaseIgnorePeriodSelf(eval_context, rewrite.rhs_const_id, phase);
}
// TODO: Process other requirements.
return info;
}
@@ -524,7 +557,8 @@ static auto PerformAggregateAccess(EvalContext& eval_context, SemIR::Inst inst)
return eval_context.GetConstantValue(elements[index]);
} else {
CARBON_CHECK(phase != Phase::Template,
"Failed to evaluate template constant {0}", inst);
"Failed to evaluate template constant {0} arg0: {1}", inst,
eval_context.insts().Get(access_inst.aggregate_id));
}
return MakeConstantResult(eval_context.context(), access_inst, phase);
}
@@ -1461,6 +1495,7 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
Phase phase = Phase::Template;
SemIR::FacetTypeInfo info = GetConstantFacetTypeInfo(
eval_context, facet_type.facet_type_id, &phase);
info.Canonicalize();
// TODO: Reuse `inst` if we can detect that nothing has changed.
return MakeFacetTypeResult(eval_context.context(), info, phase);
}
@@ -1570,21 +1605,30 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
const auto& bind_name =
eval_context.entity_names().Get(bind.entity_name_id);
// If we know which specific we're evaluating within and this is an
// argument of that specific, its constant value is the corresponding
// argument value.
if (auto value =
eval_context.GetCompileTimeBindValue(bind_name.bind_index);
value.is_valid()) {
return value;
Phase phase;
if (bind_name.name_id == SemIR::NameId::PeriodSelf) {
phase = Phase::PeriodSelfSymbolic;
} else {
// If we know which specific we're evaluating within and this is an
// argument of that specific, its constant value is the corresponding
// argument value.
if (auto value =
eval_context.GetCompileTimeBindValue(bind_name.bind_index);
value.is_valid()) {
return value;
}
phase = Phase::Symbolic;
}
// The constant form of a symbolic binding is an idealized form of the
// original, with no equivalent value.
bind.entity_name_id =
eval_context.entity_names().MakeCanonical(bind.entity_name_id);
bind.value_id = SemIR::InstId::Invalid;
return MakeConstantResult(eval_context.context(), bind, Phase::Symbolic);
if (!ReplaceFieldWithConstantValue(
eval_context, &bind, &SemIR::BindSymbolicName::type_id, &phase)) {
return MakeNonConstantResult(phase);
}
return MakeConstantResult(eval_context.context(), bind, phase);
}
// These semantic wrappers don't change the constant value.
@@ -1652,8 +1696,7 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
eval_context.insts().Get(typed_inst.period_self_id).type_id();
SemIR::Inst base_facet_inst =
eval_context.GetConstantValueAsInst(base_facet_type_id);
SemIR::FacetTypeInfo info = {.requirement_block_id =
SemIR::InstBlockId::Invalid};
SemIR::FacetTypeInfo info = {.other_requirements = false};
// `where` provides that the base facet is an error, `type`, or a facet
// type.
if (auto facet_type = base_facet_inst.TryAs<SemIR::FacetType>()) {
@@ -1666,8 +1709,29 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
"Unexpected type_id: {0}, inst: {1}", base_facet_type_id,
base_facet_inst);
}
// TODO: Combine other requirements, and then process & canonicalize them.
info.requirement_block_id = typed_inst.requirements_id;
if (typed_inst.requirements_id.is_valid()) {
auto insts = eval_context.inst_blocks().Get(typed_inst.requirements_id);
for (auto inst_id : insts) {
if (auto rewrite =
eval_context.insts().TryGetAs<SemIR::RequirementRewrite>(
inst_id)) {
SemIR::ConstantId lhs =
eval_context.GetConstantValue(rewrite->lhs_id);
SemIR::ConstantId rhs =
eval_context.GetConstantValue(rewrite->rhs_id);
// `where` requirements using `.Self` should not be considered
// symbolic
UpdatePhaseIgnorePeriodSelf(eval_context, lhs, &phase);
UpdatePhaseIgnorePeriodSelf(eval_context, rhs, &phase);
info.rewrite_constraints.push_back(
{.lhs_const_id = lhs, .rhs_const_id = rhs});
} else {
// TODO: Handle other requirements
info.other_requirements = true;
}
}
}
info.Canonicalize();
return MakeFacetTypeResult(eval_context.context(), info, phase);
}
@@ -1675,7 +1739,7 @@ static auto TryEvalInstInContext(EvalContext& eval_context,
// All other uses of unary `not` are non-constant.
case CARBON_KIND(SemIR::UnaryOperatorNot typed_inst): {
auto const_id = eval_context.GetConstantValue(typed_inst.operand_id);
auto phase = GetPhase(const_id);
auto phase = GetPhase(eval_context, const_id);
if (phase == Phase::Template) {
auto value = eval_context.insts().GetAs<SemIR::BoolLiteral>(
eval_context.constant_values().GetInstId(const_id));