[don't merge] see how much time we save when running --stage 1 in CI

.github/workflows/ci.yml

@@ -46,6 +46,9 @@ jobs:
           - name: x86_64-gnu-llvm-12
             os: ubuntu-20.04-xl
             env: {}
+          - name: x86_64-gnu-llvm-12-stage1
+            os: ubuntu-20.04-xl
+            env: {}
           - name: x86_64-gnu-tools
             env:
               CI_ONLY_WHEN_SUBMODULES_CHANGED: 1

src/ci/docker/host-x86_64/x86_64-gnu-llvm-12-stage1/Dockerfile

@@ -0,0 +1,59 @@
+FROM ubuntu:20.04
+
+ARG DEBIAN_FRONTEND=noninteractive
+RUN apt-get update && apt-get install -y --no-install-recommends \
+  g++ \
+  gcc-multilib \
+  make \
+  ninja-build \
+  file \
+  curl \
+  ca-certificates \
+  python2.7 \
+  git \
+  cmake \
+  sudo \
+  gdb \
+  llvm-12-tools \
+  llvm-12-dev \
+  libedit-dev \
+  libssl-dev \
+  pkg-config \
+  zlib1g-dev \
+  xz-utils \
+  nodejs
+
+COPY scripts/sccache.sh /scripts/
+RUN sh /scripts/sccache.sh
+
+# using llvm-link-shared due to libffi issues -- see #34486
+ENV RUST_CONFIGURE_ARGS \
+      --build=x86_64-unknown-linux-gnu \
+      --llvm-root=/usr/lib/llvm-12 \
+      --enable-llvm-link-shared \
+      --set rust.thin-lto-import-instr-limit=10
+
+# Some tests use --stage 1 to mean "build using stage1" and some using it to mean "run using stage 1".
+# Until we straighten that out, special-case the ones that mean "build with stage1".
+ENV SCRIPT python2.7 ../x.py test --exclude run-make-fulldeps --exclude error_index_generator \
+            --exclude linkchecker --stage 1 --exclude src/tools/rustdoc --exclude rustdoc-json-types \
+            --exclude tidy --exclude ui-fulldeps && \
+           # Intentionally excludes *-fulldeps, error-index, and linkchecker tests, which aren't guaranteed to work in stage 1.
+           python2.7 ../x.py test --stage 0 src/tools/rustdoc rustdoc-json-types && \
+           # Run the `mir-opt` tests again but this time for a 32-bit target.
+           # This enforces that tests using `// EMIT_MIR_FOR_EACH_BIT_WIDTH` have
+           # both 32-bit and 64-bit outputs updated by the PR author, before
+           # the PR is approved and tested for merging.
+           # It will also detect tests lacking `// EMIT_MIR_FOR_EACH_BIT_WIDTH`,
+           # despite having different output on 32-bit vs 64-bit targets.
+           python2.7 ../x.py --stage 1 test src/test/mir-opt \
+                             --host='' --target=i686-unknown-linux-gnu && \
+           # Run the UI test suite again, but in `--pass=check` mode
+           #
+           # This is intended to make sure that both `--pass=check` continues to
+           # work.
+           #
+           python2.7 ../x.py --stage 1 test src/test/ui --pass=check \
+                             --host='' --target=i686-unknown-linux-gnu && \
+           # Run tidy at the very end, after all the other tests.
+           python2.7 ../x.py --stage 1 test src/tools/tidy

src/ci/github-actions/ci.yml

@@ -287,6 +287,9 @@ jobs:
           - name: x86_64-gnu-llvm-12
             <<: *job-linux-xl
 
+          - name: x86_64-gnu-llvm-12-stage1
+            <<: *job-linux-xl
+
           - name: x86_64-gnu-tools
             env:
               CI_ONLY_WHEN_SUBMODULES_CHANGED: 1