swiftlang/swift

[SR-6154] Add support for LLVM_REVERSE_ITERATION and use it to uncover non-determinism

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#48,709 opened on 2017年10月15日

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compilergood first issue

説明
Previous ID SR-6154
Radar None
Original Reporter @gottesmm
Type Task
Votes 1
Component/s Compiler
Labels Task, StarterBug
Assignee None
Priority Medium

md5: c398112976749549e4be99b1549c89f1

Issue Description:

Upstream LLVM added an option called LLVM_REVERSE_ITERATION. This causes unordered collections to iterate in the reverse order. This can be used to uncover places in the compiler where we are using unordered collections in ways that can result in non-deterministic output.

The task is this:

1. Add build-script support and cmake support for LLVM_REVERSE_ITERATION.
2. Define a preset that does (for starters) a simple build with reverse iteration enabled. My suggestion: make sure that you specify a build directory with the name reverse iteration in it it will make binary diffing easier.
2. Add a script called ./utils/build-root-compare that performs the binary comparison given two build roots that supports an externally specified file containing an XFAIL list of binary paths.
3. Perform an initial binary comparisons in between an LLVM_REVERSE_ITERATION and a non-LLVM_REVERSE_ITERATION and XFAIL any differences.
4. At this point, we should have an iteration/reverse iteration build that can be put on a bot and maintain the current state.
5. Start going through the list of XFAILs investigating where these issues are coming from, with the bot keeping previous work from breaking.

コントリビューターガイド

技術スタック
cppshellswift
領域
build systemtooling
Issue 種別
feature
難度新しい貢献者にとっての実装難度です。1 は非常に小さな変更、5 は専門的な作業です。
4
推定時間経験ある貢献者が調査、実装、テスト、pull request 準備にかけるおおよその時間範囲です。
over 1 week
活動状況Issue が今どれだけ取り組みやすいかを示します。新しい、活発、古い、ブロック中、またはメンテナー入力待ちなどです。
stale
明確さ期待される変更、受け入れ条件、次の手順がどれだけ明確かを示します。
clear
前提条件
LLVM internalsCMakeSwift build systemShell scripting
初心者向け度初回貢献者にどれだけ取り組みやすいかを 1-100 で推定したスコアです。
10
調査方針
First, understand how the Swift build system uses CMake and build script. The issue outlines five steps: 1) Add cmake and build script support for LLVM REVERSE ITERATION. 2) Create a preset for reverse iteration build. 3) Write a script (utils/build root compare) to binary compare build roots with an XFAIL list. 4) Perform initial comparison and XFAIL any differences. 5) Plan to iterate on fixing XFAILs. The main files to look at are the build script and CMakeLists.txt. Check the swift repository's utils/ directory for existing comparison scripts. No linked PRs or assignees, so the issue is available.