commit	363a2e26e380ee353805da6e7cbd72945da6249c	[log] [tgz]
author	Ben Clayton <bclayton@google.com>	Tue Apr 13 20:07:57 2021 +0000
committer	Commit Bot service account <commit-bot@chromium.org>	Tue Apr 13 20:07:57 2021 +0000
tree	60e26514e2b033b4993184cb5d6080e58d45ba02
parent	46bb2bc93541b1c70e193da587a65798f27c555f [diff]

SymbolTable: Change behavior of anonymous symbols

SymbolTable::New() used to build and return a symbol without a registered name. When you asked for the name of the symbol it would return tint_symbol_N, where N is the numerical identifier for the symbol.

This approach was a major tripping hazzard for  transforms that liked to fetch the source program name, and register it in the new program (in this situation, you should always use `CloneContext::Clone(Symbol)`).
Without special casing for unnamed symbols, you could end up promoting the unnamed symbol to a named symbol, and then colliding against a new unnamed symbol.
This is exactly what happened in tint:711.

Instead, with this change:

* The concept of unnamed symbols has been removed. All symbols  now have a name.
* The signature of `SymbolTable::New()` has been changed to take a name parameter (which defaults to 'tint_symbol'). This can be used to create a new, unique named symbol (possibly with a suffix), which will not collide with any existing symbols. Note these symbols may still collide if `SymbolTable::Register()` is called with the same name. All Transforms that currently use `SymbolTable::Register()` will be fixed in another change.
* The CloneContext has been updated to use `SymbolTable::New()` instead of `Register()`. This means that any symbols defined before a clone will not collide.
* `CloneContext::CloneSymbols()` has been added which allows a transform to pre-clone all the symbols from the source program. This can be used to avoid the authored identifiers being suffixed with a number, in the case a transform calls New() before the symbol is cloned.
* `Symbol::to_str()` has been changed to return `$<id>` instead of `tint_symbol_N`. This is to avoid any confusion between the actual name and the symbol ID.

Bug: tint:711
Bug: tint:712
Change-Id: I526e4b49b7027545613859de487e6a275686107a
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/47631
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>

27 files changed

tree: 60e26514e2b033b4993184cb5d6080e58d45ba02

README.md

Tint

Tint is a compiler for the WebGPU Shader Language (WGSL).

This is not an officially supported Google product.

Requirements

Git
CMake (3.10.2 or later)
Ninja (or other build tool)
Python, for fetching dependencies
depot_tools in your path

Build options

TINT_BUILD_SPV_READER : enable the SPIR-V input reader (off by default)
TINT_BUILD_WGSL_READER : enable the WGSL input reader (on by default)
TINT_BUILD_SPV_WRITER : enable the SPIR-V output writer (on by default)
TINT_BUILD_WGSL_WRITER : enable the WGSL output writer (on by default)
TINT_BUILD_FUZZERS : enable building fuzzzers (off by default)

Building

Tint uses Chromium dependency management so you need to install depot_tools and add it to your PATH.

Getting source & dependencies

# Clone the repo as "tint"
git clone https://dawn.googlesource.com/tint tint
cd tint

# Bootstrap the gclient configuration
cp standalone.gclient .gclient

# Fetch external dependencies and toolchains with gclient
gclient sync

Compiling using CMake + Ninja

mkdir -p out/Debug
cd out/Debug
cmake -GNinja ../..
ninja # or autoninja

Compiling using CMake + make

mkdir -p out/Debug
cd out/Debug
cmake ../..
make # -j N for N-way parallel build

Compiling using gn + ninja

mkdir -p out/Debug
gn gen out/Debug
autoninja -C out/Debug

Fuzzers on MacOS

If you are attempting fuzz, using TINT_BUILD_FUZZERS=ON, the version of llvm in the XCode SDK does not have the needed libfuzzer functionality included.

The build error that you will see from using the XCode SDK will look something like this:

ld: file not found:/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/11.0.0/lib/darwin/libclang_rt.fuzzer_osx.a

The solution to this problem is to use a full version llvm, like what you would get via homebrew, brew install llvm, and use something like CC=<path to full clang> cmake .. to setup a build using that toolchain.

Checking [chromium-style] issues in CMake builds

The gn based work flow uses the Chromium toolchain for building in anticipation of integration of Tint into Chromium based projects. This toolchain has additional plugins for checking for style issues, which are marked with [chromium-style] in log messages. This means that this toolchain is more strict then the default clang toolchain.

In the future we will have a CQ that will build this work flow and flag issues automatically. Until that is in place, to avoid causing breakages you can run the [chromium-style] checks using the CMake based work flows. This requires setting CC to the version of clang checked out by gclient sync and setting the TINT_CHECK_CHROMIUM_STYLE to ON.

mkdir -p out/style
cd out/style
cmake ../..
CC=../../third_party/llvm-build/Release+Asserts/bin/clang cmake -DTINT_CHECK_CHROMIUM_STYLE=ON ../../ # add -GNinja for ninja builds

Issues

Please file any issues or feature requests at https://bugs.chromium.org/p/tint/issues/entry

Contributing

Please see the CONTRIBUTING and CODE_OF_CONDUCT files on how to contribute to Tint.