mirror of
https://github.com/carbon-language/carbon-lang.git
synced 2026-10-05 13:41:06 +01:00
Richard Smith
a74ca9071b
In preparation for shifting from `TypeId`s potentially representing attached types to always representing unattached types, using [terminology suggested on Discord](https://discord.com/channels/655572317891461132/963846118964350976/1359286326779973712). This change causes us to track slightly more type spelling information through SemIR. One change that has significant impact on the SemIR output is that we now build a `struct_type` instruction in each class representing the types of the fields, including the spelling used for those types. This is now no longer always identical to the corresponding canonical `struct_type` for the object representation, so it's built separately and owned by the class. Also remove `TypeBlock` support entirely, as its only use was representing `TupleType`s, which now use an `InstBlock`.
77 lines
2.9 KiB
C++
77 lines
2.9 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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#ifndef CARBON_TOOLCHAIN_SEM_IR_COPY_ON_WRITE_BLOCK_H_
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#define CARBON_TOOLCHAIN_SEM_IR_COPY_ON_WRITE_BLOCK_H_
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#include "toolchain/sem_ir/file.h"
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#include "toolchain/sem_ir/ids.h"
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namespace Carbon::SemIR {
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// A handle to a new block that may be modified, with copy-on-write semantics.
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//
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// The constructor is given the ID of an existing block that provides the
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// initial contents of the new block. The new block is lazily allocated; if no
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// modifications have been made, the `id()` function will return the original
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// block ID.
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//
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// This is intended to avoid an unnecessary block allocation in the case where
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// the new block ends up being exactly the same as the original block.
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template <typename BlockIdType, auto (SemIR::File::*ValueStore)()>
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class CopyOnWriteBlock {
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public:
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struct UninitializedBlock {
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size_t size;
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};
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// Constructs the block. `source_id` is used as the initial value of the
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// block. `file` must not be null.
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explicit CopyOnWriteBlock(SemIR::File* file, BlockIdType source_id)
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: file_(file), source_id_(source_id) {}
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// Constructs the block, treating the original block as an uninitialized block
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// with `size` elements. `file` must not be null.
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explicit CopyOnWriteBlock(SemIR::File* file, UninitializedBlock uninit)
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: file_(file),
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source_id_(BlockIdType::None),
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id_((file_->*ValueStore)().AddUninitialized(uninit.size)) {}
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// Gets a block ID containing the resulting elements. Note that further
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// modifications may or may not allocate a new ID, so this should only be
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// called once all modifications have been performed.
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auto id() const -> BlockIdType { return id_; }
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// Gets a canonical block ID containing the resulting elements. This assumes
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// the original block ID, if specified, was also canonical.
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auto GetCanonical() const -> BlockIdType {
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return id_ == source_id_ ? id_ : (file_->*ValueStore)().MakeCanonical(id_);
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}
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// Sets the element at index `i` within the block. Lazily allocates a new
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// block when the value changes for the first time.
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auto Set(int i, typename BlockIdType::ElementType value) -> void {
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if (source_id_.has_value() && (file_->*ValueStore)().Get(id_)[i] == value) {
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return;
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}
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if (id_ == source_id_) {
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id_ = (file_->*ValueStore)().Add((file_->*ValueStore)().Get(source_id_));
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}
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(file_->*ValueStore)().GetMutable(id_)[i] = value;
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}
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private:
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SemIR::File* file_;
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BlockIdType source_id_;
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BlockIdType id_ = source_id_;
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};
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using CopyOnWriteInstBlock = CopyOnWriteBlock<InstBlockId, &File::inst_blocks>;
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using CopyOnWriteStructTypeFieldsBlock =
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CopyOnWriteBlock<StructTypeFieldsId, &File::struct_type_fields>;
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} // namespace Carbon::SemIR
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#endif // CARBON_TOOLCHAIN_SEM_IR_COPY_ON_WRITE_BLOCK_H_
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