ci: add a runner for vanilla LLVM 16

Like #107044, this will let us track compatibility with LLVM 16 going
forward, especially after we eventually upgrade our own to the next.

This also drops `tidy` here and in `x86_64-gnu-llvm-15`, syncing with
that change in #106085.

.github/workflows/ci.yml

@@ -292,6 +292,10 @@ jobs:
           - name: x86_64-gnu-distcheck
             os: ubuntu-20.04-8core-32gb
             env: {}
+          - name: x86_64-gnu-llvm-16
+            env:
+              RUST_BACKTRACE: 1
+            os: ubuntu-20.04-8core-32gb
           - name: x86_64-gnu-llvm-15
             env:
               RUST_BACKTRACE: 1

src/ci/docker/host-x86_64/x86_64-gnu-llvm-15/Dockerfile

@@ -2,7 +2,6 @@ FROM ubuntu:22.10
 
 ARG DEBIAN_FRONTEND=noninteractive
 
-# NOTE: intentionally installs both python2 and python3 so we can test support for both.
 RUN apt-get update && apt-get install -y --no-install-recommends \
   g++ \
   gcc-multilib \
@@ -11,7 +10,6 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   file \
   curl \
   ca-certificates \
-  python2.7 \
   python3 \
   git \
   cmake \
@@ -63,6 +61,4 @@ ENV SCRIPT ../x.py --stage 2 test --exclude src/tools/tidy && \
            # work.
            #
            ../x.ps1 --stage 2 test tests/ui --pass=check \
-                             --host='' --target=i686-unknown-linux-gnu && \
+                             --host='' --target=i686-unknown-linux-gnu
-           # Run tidy at the very end, after all the other tests.
-           python2.7 ../x.py --stage 2 test src/tools/tidy

src/ci/docker/host-x86_64/x86_64-gnu-llvm-16/Dockerfile

@@ -0,0 +1,64 @@
+FROM ubuntu:23.04
+
+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 \
+  python3 \
+  git \
+  cmake \
+  sudo \
+  gdb \
+  llvm-16-tools \
+  llvm-16-dev \
+  libedit-dev \
+  libssl-dev \
+  pkg-config \
+  zlib1g-dev \
+  xz-utils \
+  nodejs \
+  mingw-w64 \
+  && rm -rf /var/lib/apt/lists/*
+
+# Install powershell (universal package) so we can test x.ps1 on Linux
+RUN curl -sL "https://github.com/PowerShell/PowerShell/releases/download/v7.3.1/powershell_7.3.1-1.deb_amd64.deb" > powershell.deb && \
+    dpkg -i powershell.deb && \
+    rm -f powershell.deb
+
+COPY scripts/sccache.sh /scripts/
+RUN sh /scripts/sccache.sh
+
+# We are disabling CI LLVM since this builder is intentionally using a host
+# LLVM, rather than the typical src/llvm-project LLVM.
+ENV NO_DOWNLOAD_CI_LLVM 1
+
+# 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-16 \
+      --enable-llvm-link-shared \
+      --set rust.thin-lto-import-instr-limit=10
+
+# NOTE: intentionally uses all of `x.py`, `x`, and `x.ps1` to make sure they all work on Linux.
+ENV SCRIPT ../x.py --stage 2 test --exclude src/tools/tidy && \
+           # 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.
+           ../x --stage 2 test tests/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.
+           #
+           ../x.ps1 --stage 2 test tests/ui --pass=check \
+                             --host='' --target=i686-unknown-linux-gnu

src/ci/github-actions/ci.yml

@@ -457,6 +457,11 @@ jobs:
           - name: x86_64-gnu-distcheck
             <<: *job-linux-8c
 
+          - name: x86_64-gnu-llvm-16
+            env:
+              RUST_BACKTRACE: 1
+            <<: *job-linux-8c
+
           - name: x86_64-gnu-llvm-15
             env:
               RUST_BACKTRACE: 1

tests/codegen/option-as-slice.rs

@@ -1,5 +1,7 @@
 // compile-flags: -O -Z randomize-layout=no
 // only-x86_64
+// ignore-llvm-version: 16.0.0
+// ^ needs https://reviews.llvm.org/D146149 in 16.0.1
 
 #![crate_type = "lib"]
 #![feature(option_as_slice)]

tests/debuginfo/unsized.rs

@@ -1,4 +1,6 @@
 // compile-flags:-g
+// ignore-gdb-version: 13.1 - 99.0
+// ^ https://sourceware.org/bugzilla/show_bug.cgi?id=30330
 
 // === GDB TESTS ===================================================================================