Rollup merge of #145071 - cuviper:min-llvm-20, r=nikic

Update the minimum external LLVM to 20

With this change, we'll have stable support for LLVM 20 and 21.
For reference, the previous increase to LLVM 19 was rust-lang/rust#139275.

cc ```@rust-lang/wg-llvm```
r? nikic

5 files changed, 15 insertions, 106 deletions

diff --git a/src/bootstrap/src/core/build_steps/llvm.rs b/src/bootstrap/src/core/build_steps/llvm.rs
index 83ed7430c39..d43d261ad6c 100644
--- a/src/bootstrap/src/core/build_steps/llvm.rs
+++ b/src/bootstrap/src/core/build_steps/llvm.rs
@@ -619,11 +619,11 @@ fn check_llvm_version(builder: &Builder<'_>, llvm_config: &Path) {
     let version = get_llvm_version(builder, llvm_config);
     let mut parts = version.split('.').take(2).filter_map(|s| s.parse::<u32>().ok());
     if let (Some(major), Some(_minor)) = (parts.next(), parts.next())
-        && major >= 19
+        && major >= 20
     {
         return;
     }
-    panic!("\n\nbad LLVM version: {version}, need >=19\n\n")
+    panic!("\n\nbad LLVM version: {version}, need >=20\n\n")
 }
 
 fn configure_cmake(
diff --git a/src/ci/docker/README.md b/src/ci/docker/README.md
index 488a6a2bce1..4ee02e9bf00 100644
--- a/src/ci/docker/README.md
+++ b/src/ci/docker/README.md
@@ -14,9 +14,9 @@ To run a specific CI job locally, you can use the `citool` Rust crate:
 cargo run --manifest-path src/ci/citool/Cargo.toml run-local <job-name>
 ```
 
-For example, to run the `x86_64-gnu-llvm-19-1` job:
+For example, to run the `x86_64-gnu-llvm-20-1` job:
 ```
-cargo run --manifest-path src/ci/citool/Cargo.toml run-local x86_64-gnu-llvm-19-1
+cargo run --manifest-path src/ci/citool/Cargo.toml run-local x86_64-gnu-llvm-20-1
 ```
 
 The job will output artifacts in an `obj/<image-name>` dir at the root of a repository. Note
@@ -27,10 +27,10 @@ Docker image executed in the given CI job.
 while locally, to the `obj/<image-name>` directory. This is primarily to prevent
 strange linker errors when using multiple Docker images.
 
-For some Linux workflows (for example `x86_64-gnu-llvm-19-N`), the process is more involved. You will need to see which script is executed for the given workflow inside the [`jobs.yml`](../github-actions/jobs.yml) file and pass it through the `DOCKER_SCRIPT` environment variable. For example, to reproduce the `x86_64-gnu-llvm-19-3` workflow, you can run the following script:
+For some Linux workflows (for example `x86_64-gnu-llvm-20-N`), the process is more involved. You will need to see which script is executed for the given workflow inside the [`jobs.yml`](../github-actions/jobs.yml) file and pass it through the `DOCKER_SCRIPT` environment variable. For example, to reproduce the `x86_64-gnu-llvm-20-3` workflow, you can run the following script:
 
 ```
-DOCKER_SCRIPT=x86_64-gnu-llvm3.sh ./src/ci/docker/run.sh x86_64-gnu-llvm-19
+DOCKER_SCRIPT=x86_64-gnu-llvm3.sh ./src/ci/docker/run.sh x86_64-gnu-llvm-20
 ```
 
 ## Local Development
diff --git a/src/ci/docker/host-aarch64/aarch64-gnu-llvm-19/Dockerfile b/src/ci/docker/host-aarch64/aarch64-gnu-llvm-20/Dockerfile
index e73fbe506f7..adbb1f03378 100644
--- a/src/ci/docker/host-aarch64/aarch64-gnu-llvm-19/Dockerfile
+++ b/src/ci/docker/host-aarch64/aarch64-gnu-llvm-20/Dockerfile
@@ -1,4 +1,4 @@
-FROM ubuntu:24.10
+FROM ubuntu:25.04
 
 ARG DEBIAN_FRONTEND=noninteractive
 
@@ -15,8 +15,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   cmake \
   sudo \
   gdb \
-  llvm-19-tools \
-  llvm-19-dev \
+  llvm-20-tools \
+  llvm-20-dev \
   libedit-dev \
   libssl-dev \
   pkg-config \
@@ -43,7 +43,7 @@ ENV EXTERNAL_LLVM 1
 # Using llvm-link-shared due to libffi issues -- see #34486
 ENV RUST_CONFIGURE_ARGS \
       --build=aarch64-unknown-linux-gnu \
-      --llvm-root=/usr/lib/llvm-19 \
+      --llvm-root=/usr/lib/llvm-20 \
       --enable-llvm-link-shared \
       --set rust.randomize-layout=true \
       --set rust.thin-lto-import-instr-limit=10
diff --git a/src/ci/docker/host-x86_64/x86_64-gnu-llvm-19/Dockerfile b/src/ci/docker/host-x86_64/x86_64-gnu-llvm-19/Dockerfile
deleted file mode 100644
index 5cba7c564f1..00000000000
--- a/src/ci/docker/host-x86_64/x86_64-gnu-llvm-19/Dockerfile
+++ /dev/null
@@ -1,66 +0,0 @@
-FROM ubuntu:24.10
-
-ARG DEBIAN_FRONTEND=noninteractive
-
-RUN apt-get update && apt-get install -y --no-install-recommends \
-  bzip2 \
-  g++ \
-  gcc-multilib \
-  make \
-  ninja-build \
-  file \
-  curl \
-  ca-certificates \
-  python3 \
-  git \
-  cmake \
-  sudo \
-  gdb \
-  llvm-19-tools \
-  llvm-19-dev \
-  libedit-dev \
-  libssl-dev \
-  pkg-config \
-  zlib1g-dev \
-  xz-utils \
-  nodejs \
-  mingw-w64 \
-  # libgccjit dependencies
-  flex \
-  libmpfr-dev \
-  libgmp-dev \
-  libmpc3 \
-  libmpc-dev \
-  && rm -rf /var/lib/apt/lists/*
-
-# Install powershell (universal package) so we can test x.ps1 on Linux
-# FIXME: need a "universal" version that supports libicu74, but for now it still works to ignore that dep.
-RUN curl -sL "https://github.com/PowerShell/PowerShell/releases/download/v7.3.1/powershell_7.3.1-1.deb_amd64.deb" > powershell.deb && \
-    dpkg --ignore-depends=libicu72 -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
-ENV EXTERNAL_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-19 \
-      --enable-llvm-link-shared \
-      --set rust.randomize-layout=true \
-      --set rust.thin-lto-import-instr-limit=10
-
-COPY scripts/shared.sh /scripts/
-
-COPY scripts/x86_64-gnu-llvm.sh /scripts/
-COPY scripts/x86_64-gnu-llvm2.sh /scripts/
-COPY scripts/x86_64-gnu-llvm3.sh /scripts/
-COPY scripts/stage_2_test_set1.sh /scripts/
-COPY scripts/stage_2_test_set2.sh /scripts/
-
-ENV SCRIPT "Must specify DOCKER_SCRIPT for this image"
diff --git a/src/ci/github-actions/jobs.yml b/src/ci/github-actions/jobs.yml
index 35b9456d37d..b3e3fe7d96a 100644
--- a/src/ci/github-actions/jobs.yml
+++ b/src/ci/github-actions/jobs.yml
@@ -122,19 +122,19 @@ pr:
       # tidy. This speeds up the PR CI job by ~1 minute.
       SKIP_SUBMODULES: src/gcc
     <<: *job-linux-4c
-  - name: x86_64-gnu-llvm-19
+  - name: x86_64-gnu-llvm-20
     env:
       ENABLE_GCC_CODEGEN: "1"
       DOCKER_SCRIPT: x86_64-gnu-llvm.sh
     <<: *job-linux-4c
-  - name: aarch64-gnu-llvm-19-1
+  - name: aarch64-gnu-llvm-20-1
     env:
-      IMAGE: aarch64-gnu-llvm-19
+      IMAGE: aarch64-gnu-llvm-20
       DOCKER_SCRIPT: stage_2_test_set1.sh
     <<: *job-aarch64-linux
-  - name: aarch64-gnu-llvm-19-2
+  - name: aarch64-gnu-llvm-20-2
     env:
-      IMAGE: aarch64-gnu-llvm-19
+      IMAGE: aarch64-gnu-llvm-20
       DOCKER_SCRIPT: stage_2_test_set2.sh
     <<: *job-aarch64-linux
   - name: x86_64-gnu-tools
@@ -397,31 +397,6 @@ auto:
       DOCKER_SCRIPT: x86_64-gnu-llvm3.sh
     <<: *job-linux-4c
 
-  # The x86_64-gnu-llvm-19 job is split into multiple jobs to run tests in parallel.
-  # x86_64-gnu-llvm-19-1 skips tests that run in x86_64-gnu-llvm-19-{2,3}.
-  - name: x86_64-gnu-llvm-19-1
-    env:
-      RUST_BACKTRACE: 1
-      IMAGE: x86_64-gnu-llvm-19
-      DOCKER_SCRIPT: stage_2_test_set2.sh
-    <<: *job-linux-4c
-
-  # Skip tests that run in x86_64-gnu-llvm-19-{1,3}
-  - name: x86_64-gnu-llvm-19-2
-    env:
-      RUST_BACKTRACE: 1
-      IMAGE: x86_64-gnu-llvm-19
-      DOCKER_SCRIPT: x86_64-gnu-llvm2.sh
-    <<: *job-linux-4c
-
-  # Skip tests that run in x86_64-gnu-llvm-19-{1,2}
-  - name: x86_64-gnu-llvm-19-3
-    env:
-      RUST_BACKTRACE: 1
-      IMAGE: x86_64-gnu-llvm-19
-      DOCKER_SCRIPT: x86_64-gnu-llvm3.sh
-    <<: *job-linux-4c
-
   - name: x86_64-gnu-nopt
     <<: *job-linux-4c