[llvm] [CI] Update Windows testing to use clang compiler. (PR #162026)

[via llvm-commits]

https://github.com/cmtice updated https://github.com/llvm/llvm-project/pull/162026

>From e5106e4ed70a772096aa5c73a7072ef50b966a74 Mon Sep 17 00:00:00 2001
From: Caroline Tice <cmtice at google.com>
Date: Sun, 5 Oct 2025 12:39:44 -0700
Subject: [PATCH 1/5] [CI] Update Windows testing to use clang compiler.

Test whether or not using clang for premerge testing on Windows
will improve performance.

Currently a work-in-progress: DO NOT REVIEW! DO NOT COMMIT!
---
 .ci/monolithic-windows.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/.ci/monolithic-windows.sh b/.ci/monolithic-windows.sh
index f85d6e3d51b57..5ad4899188f20 100755
--- a/.ci/monolithic-windows.sh
+++ b/.ci/monolithic-windows.sh
@@ -23,8 +23,8 @@ runtimes_targets="${4}"
 start-group "CMake"
 pip install -q -r "${MONOREPO_ROOT}"/.ci/all_requirements.txt
 
-export CC=cl
-export CXX=cl
+export CC=clang-cl
+export CXX=clang-cl
 export LD=link
 
 # The CMAKE_*_LINKER_FLAGS to disable the manifest come from research

>From cc89d8c05a39685f84b0e4e24d962a00611c4feb Mon Sep 17 00:00:00 2001
From: Caroline Tice <cmtice at google.com>
Date: Sun, 5 Oct 2025 12:50:04 -0700
Subject: [PATCH 2/5] Try to find clang compiler.

---
 .ci/monolithic-windows.sh | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/.ci/monolithic-windows.sh b/.ci/monolithic-windows.sh
index 5ad4899188f20..51cde5f4fc878 100755
--- a/.ci/monolithic-windows.sh
+++ b/.ci/monolithic-windows.sh
@@ -23,6 +23,8 @@ runtimes_targets="${4}"
 start-group "CMake"
 pip install -q -r "${MONOREPO_ROOT}"/.ci/all_requirements.txt
 
+which clang-cl
+
 export CC=clang-cl
 export CXX=clang-cl
 export LD=link

>From f724bfed7e758a57b56f12d6903bffbace47da4d Mon Sep 17 00:00:00 2001
From: Caroline Tice <cmtice at google.com>
Date: Sun, 5 Oct 2025 20:46:10 -0700
Subject: [PATCH 3/5] Attempt to download the clang tarball.

---
 .ci/monolithic-windows.sh | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/.ci/monolithic-windows.sh b/.ci/monolithic-windows.sh
index 51cde5f4fc878..e82b525d47ce7 100755
--- a/.ci/monolithic-windows.sh
+++ b/.ci/monolithic-windows.sh
@@ -23,7 +23,12 @@ runtimes_targets="${4}"
 start-group "CMake"
 pip install -q -r "${MONOREPO_ROOT}"/.ci/all_requirements.txt
 
-which clang-cl
+mkdir /tmp/clang-download
+pushd /tmp/clang-download
+curl -L -o "clang+llvm-21.1.2-x86_64-pc-windows.msvc.tar.xz" http://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.2/ckabg+llvm-21.1.2-x86_64-pc-windows.msvc.tar.xz
+ls -l "clang+llvm-21.1.2-x86_64-pc-windows.msvc.tar.xz"
+
+
 
 export CC=clang-cl
 export CXX=clang-cl

>From 120878da5ec1839b39cbef069a8b8305173452e2 Mon Sep 17 00:00:00 2001
From: Caroline Tice <cmtice at google.com>
Date: Sun, 5 Oct 2025 21:09:58 -0700
Subject: [PATCH 4/5] Decompress and unpack the clang tarball.

---
 .ci/monolithic-windows.sh | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/.ci/monolithic-windows.sh b/.ci/monolithic-windows.sh
index e82b525d47ce7..8d6b5b3de633a 100755
--- a/.ci/monolithic-windows.sh
+++ b/.ci/monolithic-windows.sh
@@ -25,8 +25,11 @@ pip install -q -r "${MONOREPO_ROOT}"/.ci/all_requirements.txt
 
 mkdir /tmp/clang-download
 pushd /tmp/clang-download
-curl -L -o "clang+llvm-21.1.2-x86_64-pc-windows.msvc.tar.xz" http://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.2/ckabg+llvm-21.1.2-x86_64-pc-windows.msvc.tar.xz
-ls -l "clang+llvm-21.1.2-x86_64-pc-windows.msvc.tar.xz"
+curl -L -o "clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar.xz" http://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.2/clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar.xz
+ls -l "clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar.xz"
+unxz "clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar.xz"
+tar xvf "clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar"
+ls -l /tmp/clang-download/clang+llvm-21.1.2-x86_64-pc-windows-msvc/bin/clang-cl.exe
 
 
 

>From d69c6afd5fc871da8345f75a5832b2cb4468b237 Mon Sep 17 00:00:00 2001
From: Caroline Tice <cmtice at google.com>
Date: Sun, 5 Oct 2025 21:32:04 -0700
Subject: [PATCH 5/5] Try an alternate decompression technique.

---
 .ci/monolithic-windows.sh | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/.ci/monolithic-windows.sh b/.ci/monolithic-windows.sh
index 8d6b5b3de633a..b4f8a50e01df1 100755
--- a/.ci/monolithic-windows.sh
+++ b/.ci/monolithic-windows.sh
@@ -27,8 +27,7 @@ mkdir /tmp/clang-download
 pushd /tmp/clang-download
 curl -L -o "clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar.xz" http://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.2/clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar.xz
 ls -l "clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar.xz"
-unxz "clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar.xz"
-tar xvf "clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar"
+tar xJvf "clang+llvm-21.1.2-x86_64-pc-windows-msvc.tar.xz"
 ls -l /tmp/clang-download/clang+llvm-21.1.2-x86_64-pc-windows-msvc/bin/clang-cl.exe