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580e84513c
Documents the scheme thus far, as implemented in
a548eff0bb
---------
Co-authored-by: Geoff Romer <gromer@google.com>
Co-authored-by: Carbon Infra Bot <carbon-external-infra@google.com>
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
88 lines
2.2 KiB
Markdown
88 lines
2.2 KiB
Markdown
# Lower
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<!--
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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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-->
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<!-- toc -->
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## Table of contents
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- [Overview](#overview)
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- [Mangling](#mangling)
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- [Examples](#examples)
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<!-- tocstop -->
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## Overview
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Lowering takes the SemIR and produces LLVM IR. At present, this is done in a
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single pass, although it's possible we may need to do a second pass so that we
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can first generate type information for function arguments.
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Lowering is done per `SemIR::InstBlock`. This minimizes changes to the
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`IRBuilder` insertion point, something that is both expensive and potentially
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fragile.
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## Mangling
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Part of lowering is choosing deterministically unique identifiers for each
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lowered entity to use in platform object files. Any feature of an entity (such
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as parent namespaces or overloaded function parameters) that would create a
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distinct entity must be included in some way in the generated identifier.
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The current rudimentary name mangling scheme is as follows:
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- As a special case, `Main.Run` is emitted as `main`.
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Otherwise the resulting name consists of:
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1. `_C`
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2. The unqualified function name (function name mangling is the only thing
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implemented at the moment).
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3. `.`
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4. If the function being mangled is a member of:
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- an `impl`, then add:
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1. The implementing type, per the scope mangling.
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2. `:`
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3. The interface type, per the scope mangling.
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- a type or namespace, then add:
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1. The scope, per the scope mangling.
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The scope mangling scheme is as follows:
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1. The unqualified name of the type or namespace.
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2. If the type or namespace is within another type or namespace:
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1. `.`
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2. The enclosing scope, per the scope mangling.
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3. `.`
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4. The package name.
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### Examples
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```carbon
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package P1;
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interface Interface {
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fn Op[self: Self]();
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}
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```
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```carbon
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namespace NameSpace;
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class NameSpace.Implementation {
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// Mangled as:
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// `_COp.Implementation.NameSpace.Main:Interface.P1`
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impl as P1.Interface {
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fn Op[self: Self]() {
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}
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}
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}
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// Mangled as `main`.
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fn Run() {
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var v: NameSpace.Implementation;
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v.(P1.Interface.Op)();
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}
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```
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