mirror of
https://github.com/carbon-language/carbon-lang.git
synced 2026-09-24 22:02:23 +01:00
Richard Smith
439a644960
To avoid bouncing through `constant_values()` to determine whether a type is symbolic or template, store the `ConstantId` on the `TypeInfo` not just the `InstId`. In addition to propagating the symbolic / template phase, this also propagates whether a type contains an error, resulting in our no longer producing types such as `<error>*` -- these now evaluate to simply `<error>`. While this makes our types less precise after an error, it also removes some follow-on diagnostics, so it seems to be an improvement on the whole.
493 lines
20 KiB
C++
493 lines
20 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#include "toolchain/check/eval.h"
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#include "toolchain/sem_ir/ids.h"
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#include "toolchain/sem_ir/typed_insts.h"
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#include "toolchain/sem_ir/value_stores.h"
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namespace Carbon::Check {
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namespace {
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// The evaluation phase for an expression, computed by evaluation. These are
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// ordered so that the phase of an expression is the numerically highest phase
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// of its constituent evaluations. Note that an expression with any runtime
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// component is known to have Runtime phase even if it involves an evaluation
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// with UnknownDueToError phase.
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enum class Phase : uint8_t {
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// Value could be entirely and concretely computed.
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Template,
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// Evaluation phase is symbolic because the expression involves a reference to
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// a symbolic binding.
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Symbolic,
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// The evaluation phase is unknown because evaluation encountered an
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// already-diagnosed semantic or syntax error. This is treated as being
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// potentially constant, but with an unknown phase.
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UnknownDueToError,
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// The expression has runtime phase because of a non-constant subexpression.
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Runtime,
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};
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} // namespace
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// Gets the phase in which the value of a constant will become available.
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static auto GetPhase(SemIR::ConstantId constant_id) -> Phase {
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if (!constant_id.is_constant()) {
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return Phase::Runtime;
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} else if (constant_id == SemIR::ConstantId::Error) {
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return Phase::UnknownDueToError;
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} else if (constant_id.is_template()) {
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return Phase::Template;
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} else {
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return Phase::Symbolic;
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}
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}
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// Returns the later of two phases.
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static auto LatestPhase(Phase a, Phase b) -> Phase {
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return static_cast<Phase>(
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std::max(static_cast<uint8_t>(a), static_cast<uint8_t>(b)));
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}
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// Forms a `constant_id` describing a given evaluation result.
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static auto MakeConstantResult(Context& context, SemIR::Inst inst, Phase phase)
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-> SemIR::ConstantId {
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switch (phase) {
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case Phase::Template:
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return context.AddConstant(inst, /*is_symbolic=*/false);
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case Phase::Symbolic:
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return context.AddConstant(inst, /*is_symbolic=*/true);
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case Phase::UnknownDueToError:
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return SemIR::ConstantId::Error;
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case Phase::Runtime:
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return SemIR::ConstantId::NotConstant;
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}
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}
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// Forms a `constant_id` describing why an evaluation was not constant.
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static auto MakeNonConstantResult(Phase phase) -> SemIR::ConstantId {
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return phase == Phase::UnknownDueToError ? SemIR::ConstantId::Error
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: SemIR::ConstantId::NotConstant;
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}
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// `GetConstantValue` checks to see whether the provided ID describes a value
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// with constant phase, and if so, returns the corresponding constant value.
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// Overloads are provided for different kinds of ID.
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// If the given instruction is constant, returns its constant value.
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static auto GetConstantValue(Context& context, SemIR::InstId inst_id,
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Phase* phase) -> SemIR::InstId {
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auto const_id = context.constant_values().Get(inst_id);
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*phase = LatestPhase(*phase, GetPhase(const_id));
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return const_id.inst_id();
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}
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// A type is always constant, but we still need to extract its phase.
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static auto GetConstantValue(Context& context, SemIR::TypeId type_id,
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Phase* phase) -> SemIR::TypeId {
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auto const_id = context.types().GetConstantId(type_id);
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*phase = LatestPhase(*phase, GetPhase(const_id));
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return type_id;
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}
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// If the given instruction block contains only constants, returns a
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// corresponding block of those values.
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static auto GetConstantValue(Context& context, SemIR::InstBlockId inst_block_id,
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Phase* phase) -> SemIR::InstBlockId {
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auto insts = context.inst_blocks().Get(inst_block_id);
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llvm::SmallVector<SemIR::InstId> const_insts;
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for (auto inst_id : insts) {
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auto const_inst_id = GetConstantValue(context, inst_id, phase);
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if (!const_inst_id.is_valid()) {
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return SemIR::InstBlockId::Invalid;
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}
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// Once we leave the small buffer, we know the first few elements are all
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// constant, so it's likely that the entire block is constant. Resize to the
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// target size given that we're going to allocate memory now anyway.
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if (const_insts.size() == const_insts.capacity()) {
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const_insts.reserve(insts.size());
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}
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const_insts.push_back(const_inst_id);
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}
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// TODO: If the new block is identical to the original block, return the
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// original ID.
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return context.inst_blocks().Add(const_insts);
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}
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// The constant value of a type block is that type block, but we still need to
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// extract its phase.
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static auto GetConstantValue(Context& context, SemIR::TypeBlockId type_block_id,
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Phase* phase) -> SemIR::TypeBlockId {
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auto types = context.type_blocks().Get(type_block_id);
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for (auto type_id : types) {
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GetConstantValue(context, type_id, phase);
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}
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return type_block_id;
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}
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// Replaces the specified field of the given typed instruction with its constant
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// value, if it has constant phase. Returns true on success, false if the value
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// has runtime phase.
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template <typename InstT, typename FieldIdT>
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static auto ReplaceFieldWithConstantValue(Context& context, InstT* inst,
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FieldIdT InstT::*field, Phase* phase)
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-> bool {
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auto unwrapped = GetConstantValue(context, inst->*field, phase);
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if (!unwrapped.is_valid()) {
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return false;
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}
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inst->*field = unwrapped;
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return true;
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}
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// If the specified fields of the given typed instruction have constant values,
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// replaces the fields with their constant values and builds a corresponding
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// constant value. Otherwise returns `ConstantId::NotConstant`. Returns
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// `ConstantId::Error` if any subexpression is an error.
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//
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// The constant value is then checked by calling `validate_fn(typed_inst)`,
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// which should return a `bool` indicating whether the new constant is valid. If
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// validation passes, a corresponding ConstantId for the new constant is
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// returned. If validation fails, it should produce a suitable error message.
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// `ConstantId::Error` is returned.
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template <typename InstT, typename ValidateFn, typename... EachFieldIdT>
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static auto RebuildAndValidateIfFieldsAreConstant(
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Context& context, SemIR::Inst inst, ValidateFn validate_fn,
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EachFieldIdT InstT::*... each_field_id) -> SemIR::ConstantId {
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// Build a constant instruction by replacing each non-constant operand with
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// its constant value.
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auto typed_inst = inst.As<InstT>();
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Phase phase = Phase::Template;
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if ((ReplaceFieldWithConstantValue(context, &typed_inst, each_field_id,
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&phase) &&
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...)) {
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if (!validate_fn(typed_inst)) {
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return SemIR::ConstantId::Error;
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}
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return MakeConstantResult(context, typed_inst, phase);
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}
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return MakeNonConstantResult(phase);
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}
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// Same as above but with no validation step.
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template <typename InstT, typename... EachFieldIdT>
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static auto RebuildIfFieldsAreConstant(Context& context, SemIR::Inst inst,
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EachFieldIdT InstT::*... each_field_id)
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-> SemIR::ConstantId {
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return RebuildAndValidateIfFieldsAreConstant(
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context, inst, [](...) { return true; }, each_field_id...);
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}
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// Rebuilds the given aggregate initialization instruction as a corresponding
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// constant aggregate value, if its elements are all constants.
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static auto RebuildInitAsValue(Context& context, SemIR::Inst inst,
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SemIR::InstKind value_kind)
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-> SemIR::ConstantId {
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auto init_inst = inst.As<SemIR::AnyAggregateInit>();
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Phase phase = Phase::Template;
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auto elements_id = GetConstantValue(context, init_inst.elements_id, &phase);
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return MakeConstantResult(
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context,
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SemIR::AnyAggregateValue{.kind = value_kind,
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.type_id = init_inst.type_id,
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.elements_id = elements_id},
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phase);
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}
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// Performs an access into an aggregate, retrieving the specified element.
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static auto PerformAggregateAccess(Context& context, SemIR::Inst inst)
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-> SemIR::ConstantId {
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auto access_inst = inst.As<SemIR::AnyAggregateAccess>();
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Phase phase = Phase::Template;
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if (auto aggregate_id =
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GetConstantValue(context, access_inst.aggregate_id, &phase);
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aggregate_id.is_valid()) {
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if (auto aggregate =
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context.insts().TryGetAs<SemIR::AnyAggregateValue>(aggregate_id)) {
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auto elements = context.inst_blocks().Get(aggregate->elements_id);
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auto index = static_cast<size_t>(access_inst.index.index);
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CARBON_CHECK(index < elements.size()) << "Access out of bounds.";
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// `Phase` is not used here. If this element is a template constant, then
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// so is the result of indexing, even if the aggregate also contains a
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// symbolic context.
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return context.constant_values().Get(elements[index]);
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} else {
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CARBON_CHECK(phase != Phase::Template)
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<< "Failed to evaluate template constant " << inst;
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}
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}
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return MakeNonConstantResult(phase);
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}
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// Performs an index into a homogeneous aggregate, retrieving the specified
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// element.
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static auto PerformAggregateIndex(Context& context, SemIR::Inst inst)
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-> SemIR::ConstantId {
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auto index_inst = inst.As<SemIR::AnyAggregateIndex>();
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Phase phase = Phase::Template;
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auto aggregate_id =
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GetConstantValue(context, index_inst.aggregate_id, &phase);
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auto index_id = GetConstantValue(context, index_inst.index_id, &phase);
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if (!index_id.is_valid()) {
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return MakeNonConstantResult(phase);
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}
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auto index = context.insts().TryGetAs<SemIR::IntLiteral>(index_id);
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if (!index) {
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CARBON_CHECK(phase != Phase::Template)
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<< "Template constant integer should be a literal";
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return MakeNonConstantResult(phase);
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}
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// Array indexing is invalid if the index is constant and out of range.
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auto aggregate_type_id =
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context.insts().Get(index_inst.aggregate_id).type_id();
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const auto& index_val = context.ints().Get(index->int_id);
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if (auto array_type =
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context.types().TryGetAs<SemIR::ArrayType>(aggregate_type_id)) {
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if (auto bound =
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context.insts().TryGetAs<SemIR::IntLiteral>(array_type->bound_id)) {
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// This awkward call to `getZExtValue` is a workaround for APInt not
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// supporting comparisons between integers of different bit widths.
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if (index_val.getActiveBits() > 64 ||
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context.ints().Get(bound->int_id).ule(index_val.getZExtValue())) {
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CARBON_DIAGNOSTIC(ArrayIndexOutOfBounds, Error,
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"Array index `{0}` is past the end of type `{1}`.",
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llvm::APSInt, std::string);
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context.emitter().Emit(
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index_inst.index_id, ArrayIndexOutOfBounds,
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llvm::APSInt(index_val, /*isUnsigned=*/true),
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context.sem_ir().StringifyType(aggregate_type_id));
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return SemIR::ConstantId::Error;
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}
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}
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}
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if (!aggregate_id.is_valid()) {
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return MakeNonConstantResult(phase);
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}
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auto aggregate =
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context.insts().TryGetAs<SemIR::AnyAggregateValue>(aggregate_id);
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if (!aggregate) {
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CARBON_CHECK(phase != Phase::Template)
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<< "Unexpected representation for template constant aggregate";
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return MakeNonConstantResult(phase);
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}
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auto elements = context.inst_blocks().Get(aggregate->elements_id);
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// We checked this for the array case above.
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CARBON_CHECK(index_val.ult(elements.size()))
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<< "Index out of bounds in tuple indexing";
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return context.constant_values().Get(elements[index_val.getZExtValue()]);
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}
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auto TryEvalInst(Context& context, SemIR::InstId inst_id, SemIR::Inst inst)
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-> SemIR::ConstantId {
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// TODO: Ensure we have test coverage for each of these cases that can result
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// in a constant, once those situations are all reachable.
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// clang warns on unhandled enum values; clang-tidy is incorrect here.
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// NOLINTNEXTLINE(bugprone-switch-missing-default-case)
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switch (inst.kind()) {
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// These cases are constants if their operands are.
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case SemIR::AddrOf::Kind:
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return RebuildIfFieldsAreConstant(context, inst,
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&SemIR::AddrOf::lvalue_id);
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case SemIR::ArrayType::Kind:
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return RebuildAndValidateIfFieldsAreConstant(
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context, inst,
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[&](SemIR::ArrayType result) {
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auto bound_id = inst.As<SemIR::ArrayType>().bound_id;
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auto int_bound =
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context.insts().TryGetAs<SemIR::IntLiteral>(result.bound_id);
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if (!int_bound) {
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// TODO: Permit symbolic array bounds. This will require fixing
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// callers of `GetArrayBoundValue`.
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context.TODO(context.insts().GetParseNode(bound_id),
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"symbolic array bound");
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return false;
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}
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// TODO: We should check that the size of the resulting array type
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// fits in 64 bits, not just that the bound does. Should we use a
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// 32-bit limit for 32-bit targets?
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// TODO: Also check for a negative bound, once that's something we
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// can represent.
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const auto& bound_val = context.ints().Get(int_bound->int_id);
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if (bound_val.getActiveBits() > 64) {
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CARBON_DIAGNOSTIC(ArrayBoundTooLarge, Error,
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"Array bound of {0} is too large.",
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llvm::APInt);
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context.emitter().Emit(bound_id, ArrayBoundTooLarge, bound_val);
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return false;
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}
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return true;
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},
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&SemIR::ArrayType::bound_id, &SemIR::ArrayType::element_type_id);
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case SemIR::BoundMethod::Kind:
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return RebuildIfFieldsAreConstant(context, inst,
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&SemIR::BoundMethod::object_id,
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&SemIR::BoundMethod::function_id);
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case SemIR::PointerType::Kind:
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return RebuildIfFieldsAreConstant(context, inst,
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&SemIR::PointerType::pointee_id);
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case SemIR::StructType::Kind:
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return RebuildIfFieldsAreConstant(context, inst,
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&SemIR::StructType::fields_id);
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case SemIR::StructTypeField::Kind:
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return RebuildIfFieldsAreConstant(context, inst,
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&SemIR::StructTypeField::field_type_id);
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case SemIR::StructValue::Kind:
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return RebuildIfFieldsAreConstant(context, inst,
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&SemIR::StructValue::elements_id);
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case SemIR::TupleType::Kind:
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return RebuildIfFieldsAreConstant(context, inst,
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&SemIR::TupleType::elements_id);
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case SemIR::TupleValue::Kind:
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return RebuildIfFieldsAreConstant(context, inst,
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&SemIR::TupleValue::elements_id);
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case SemIR::UnboundElementType::Kind:
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return RebuildIfFieldsAreConstant(
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context, inst, &SemIR::UnboundElementType::class_type_id,
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&SemIR::UnboundElementType::element_type_id);
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// Initializers evaluate to a value of the object representation.
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case SemIR::ArrayInit::Kind:
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// TODO: Add an `ArrayValue` to represent a constant array object
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// representation instead of using a `TupleValue`.
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return RebuildInitAsValue(context, inst, SemIR::TupleValue::Kind);
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case SemIR::ClassInit::Kind:
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// TODO: Add a `ClassValue` to represent a constant class object
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// representation instead of using a `StructValue`.
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return RebuildInitAsValue(context, inst, SemIR::StructValue::Kind);
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case SemIR::StructInit::Kind:
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return RebuildInitAsValue(context, inst, SemIR::StructValue::Kind);
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case SemIR::TupleInit::Kind:
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return RebuildInitAsValue(context, inst, SemIR::TupleValue::Kind);
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// These cases are always template constants.
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case SemIR::Builtin::Kind:
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case SemIR::ClassType::Kind:
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// TODO: Once classes have generic arguments, handle them.
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return MakeConstantResult(context, inst, Phase::Template);
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// These cases are treated as being the unique canonical definition of the
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// corresponding constant value.
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// TODO: This doesn't properly handle redeclarations. Consider adding a
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// corresponding `Value` inst for each of these cases.
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case SemIR::BaseDecl::Kind:
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case SemIR::FieldDecl::Kind:
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case SemIR::FunctionDecl::Kind:
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case SemIR::Namespace::Kind:
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return SemIR::ConstantId::ForTemplateConstant(inst_id);
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case SemIR::BoolLiteral::Kind:
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case SemIR::IntLiteral::Kind:
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case SemIR::RealLiteral::Kind:
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case SemIR::StringLiteral::Kind:
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// Promote literals to the constant block.
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// TODO: Convert literals into a canonical form. Currently we can form two
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// different `i32` constants with the same value if they are represented
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// by `APInt`s with different bit widths.
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return MakeConstantResult(context, inst, Phase::Template);
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// The elements of a constant aggregate can be accessed.
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case SemIR::ClassElementAccess::Kind:
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case SemIR::StructAccess::Kind:
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case SemIR::TupleAccess::Kind:
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return PerformAggregateAccess(context, inst);
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case SemIR::ArrayIndex::Kind:
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case SemIR::TupleIndex::Kind:
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return PerformAggregateIndex(context, inst);
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// TODO: These need special handling.
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case SemIR::BindValue::Kind:
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case SemIR::Call::Kind:
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case SemIR::CrossRef::Kind:
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case SemIR::Deref::Kind:
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case SemIR::Temporary::Kind:
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case SemIR::TemporaryStorage::Kind:
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case SemIR::ValueAsRef::Kind:
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break;
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case SemIR::BindSymbolicName::Kind:
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// TODO: Consider forming a constant value here using a de Bruijn index or
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// similar, so that corresponding symbolic parameters in redeclarations
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// are treated as the same value.
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return SemIR::ConstantId::ForSymbolicConstant(inst_id);
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// These semnatic wrappers don't change the constant value.
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case SemIR::NameRef::Kind:
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return context.constant_values().Get(inst.As<SemIR::NameRef>().value_id);
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case SemIR::Converted::Kind:
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return context.constant_values().Get(
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inst.As<SemIR::Converted>().result_id);
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case SemIR::InitializeFrom::Kind:
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return context.constant_values().Get(
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inst.As<SemIR::InitializeFrom>().src_id);
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case SemIR::SpliceBlock::Kind:
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return context.constant_values().Get(
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inst.As<SemIR::SpliceBlock>().result_id);
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case SemIR::ValueOfInitializer::Kind:
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return context.constant_values().Get(
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inst.As<SemIR::ValueOfInitializer>().init_id);
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// `not true` -> `false`, `not false` -> `true`.
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// All other uses of unary `not` are non-constant.
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case SemIR::UnaryOperatorNot::Kind: {
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auto const_id = context.constant_values().Get(
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inst.As<SemIR::UnaryOperatorNot>().operand_id);
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auto phase = GetPhase(const_id);
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if (phase == Phase::Template) {
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auto value =
|
|
context.insts().GetAs<SemIR::BoolLiteral>(const_id.inst_id());
|
|
value.value =
|
|
(value.value == SemIR::BoolValue::False ? SemIR::BoolValue::True
|
|
: SemIR::BoolValue::False);
|
|
return MakeConstantResult(context, value, Phase::Template);
|
|
}
|
|
if (phase == Phase::UnknownDueToError) {
|
|
return SemIR::ConstantId::Error;
|
|
}
|
|
break;
|
|
}
|
|
|
|
// `const (const T)` evaluates to `const T`. Otherwise, `const T` evaluates
|
|
// to itself.
|
|
case SemIR::ConstType::Kind: {
|
|
auto inner_id = context.constant_values().Get(
|
|
context.types().GetInstId(inst.As<SemIR::ConstType>().inner_id));
|
|
if (inner_id.is_constant() &&
|
|
context.insts().Get(inner_id.inst_id()).Is<SemIR::ConstType>()) {
|
|
return inner_id;
|
|
}
|
|
return MakeConstantResult(context, inst, GetPhase(inner_id));
|
|
}
|
|
|
|
// These cases are either not expressions or not constant.
|
|
case SemIR::AddrPattern::Kind:
|
|
case SemIR::Assign::Kind:
|
|
case SemIR::BindName::Kind:
|
|
case SemIR::BlockArg::Kind:
|
|
case SemIR::Branch::Kind:
|
|
case SemIR::BranchIf::Kind:
|
|
case SemIR::BranchWithArg::Kind:
|
|
case SemIR::ClassDecl::Kind:
|
|
case SemIR::Import::Kind:
|
|
case SemIR::InterfaceDecl::Kind:
|
|
case SemIR::LazyImportRef::Kind:
|
|
case SemIR::Param::Kind:
|
|
case SemIR::ReturnExpr::Kind:
|
|
case SemIR::Return::Kind:
|
|
case SemIR::StructLiteral::Kind:
|
|
case SemIR::TupleLiteral::Kind:
|
|
case SemIR::VarStorage::Kind:
|
|
break;
|
|
}
|
|
return SemIR::ConstantId::NotConstant;
|
|
}
|
|
|
|
} // namespace Carbon::Check
|