Learn the LLVM regression test workflow

Time: About 150 minutes: 40 reading, 80 lab, 20 testing, 10 notes.
Prerequisites: Day 02: Prepare a reproducible learning environment, Day 13: Navigate the Clang source tree

Toolchain: current-main build

Use build/bin/clang++ and build/bin/llvm-lit from your llvm-main checkout, not whichever clang++ is first on PATH. Reproduce upstream behavior on current main and record the commit SHA. Setup guide

Learn

lit, RUN lines, substitutions and diagnostic expectations.

Read Reading

R10 · LLVM testing guide
Regression testing · 25 min
R11 · Hacking on Clang
Testing and debugging sections; prefer the current CMake workflow · 15 min

Reading budgets cover selected sections, not whole chapters. Link to the book; this site does not reproduce it.

Build Build or investigate

Build Clang test dependencies.
Run one existing SemaCXX test through build/bin/llvm-lit.
Make a temporary scratch test with the diagnostic example in the commands section.
Deliberately break its expected message, observe failure, then restore it.

Done when

A recorded passing and intentionally failing lit run, including the exact compiler path.

Recall question

Why should %clang_cc1 appear in a test RUN line rather than be typed into your shell?

Completion checks

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Notes

Saved only in this browser. Keep it short enough to finish in ten minutes; none of the prompts are required. All notes, export and import