diff --git a/.ci/generate-buildkite-pipeline-premerge b/.ci/generate-buildkite-pipeline-premerge
index 7676ff716c418..363efe9ae5fb5 100755
--- a/.ci/generate-buildkite-pipeline-premerge
+++ b/.ci/generate-buildkite-pipeline-premerge
@@ -272,7 +272,7 @@ if [[ "${linux_projects}" != "" ]]; then
   artifact_paths:
   - 'artifacts/**/*'
   - '*_result.json'
-  - 'build/test-results.xml'
+  - 'build/*-test-results.xml'
   agents: ${LINUX_AGENTS}
   retry:
     automatic:
@@ -289,27 +289,27 @@ if [[ "${linux_projects}" != "" ]]; then
 EOF
 fi
 
-if [[ "${windows_projects}" != "" ]]; then
-  cat <<EOF
-- label: ':windows: Windows x64'
-  artifact_paths:
-  - 'artifacts/**/*'
-  - '*_result.json'
-  - 'build/test-results.xml'
-  agents: ${WINDOWS_AGENTS}
-  retry:
-    automatic:
-      - exit_status: -1  # Agent was lost
-        limit: 2
-      - exit_status: 255 # Forced agent shutdown
-        limit: 2
-  timeout_in_minutes: 150
-  env:
-    CC: 'cl'
-    CXX: 'cl'
-    LD: 'link'
-  commands:
-  - 'C:\\BuildTools\\Common7\\Tools\\VsDevCmd.bat -arch=amd64 -host_arch=amd64'
-  - 'bash .ci/monolithic-windows.sh "$(echo ${windows_projects} | tr ' ' ';')" "$(echo ${windows_check_targets})"'
-EOF
-fi
+# if [[ "${windows_projects}" != "" ]]; then
+#   cat <<EOF
+# - label: ':windows: Windows x64'
+#   artifact_paths:
+#   - 'artifacts/**/*'
+#   - '*_result.json'
+#   - 'build/test-results.xml'
+#   agents: ${WINDOWS_AGENTS}
+#   retry:
+#     automatic:
+#       - exit_status: -1  # Agent was lost
+#         limit: 2
+#       - exit_status: 255 # Forced agent shutdown
+#         limit: 2
+#   timeout_in_minutes: 150
+#   env:
+#     CC: 'cl'
+#     CXX: 'cl'
+#     LD: 'link'
+#   commands:
+#   - 'C:\\BuildTools\\Common7\\Tools\\VsDevCmd.bat -arch=amd64 -host_arch=amd64'
+#   - 'bash .ci/monolithic-windows.sh "$(echo ${windows_projects} | tr ' ' ';')" "$(echo ${windows_check_targets})"'
+# EOF
+# fi
diff --git a/.ci/generate_test_report.py b/.ci/generate_test_report.py
new file mode 100644
index 0000000000000..f2ae116ace99a
--- /dev/null
+++ b/.ci/generate_test_report.py
@@ -0,0 +1,328 @@
+# Script to parse many JUnit XML result files and send a report to the buildkite
+# agent as an annotation.
+#
+# To run the unittests:
+# python3 -m unittest discover -p generate_test_report.py
+
+import argparse
+import unittest
+from io import StringIO
+from junitparser import JUnitXml, Failure
+from textwrap import dedent
+from subprocess import check_call
+
+
+def junit_from_xml(xml):
+    return JUnitXml.fromfile(StringIO(xml))
+
+
+class TestReports(unittest.TestCase):
+    def test_title_only(self):
+        self.assertEqual(_generate_report("Foo", []), ("", None))
+
+    def test_no_tests_in_testsuite(self):
+        self.assertEqual(
+            _generate_report(
+                "Foo",
+                [
+                    junit_from_xml(
+                        dedent(
+                            """\
+          <?xml version="1.0" encoding="UTF-8"?>
+          <testsuites time="0.00">
+          <testsuite name="Empty" tests="0" failures="0" skipped="0" time="0.00">
+          </testsuite>
+          </testsuites>"""
+                        )
+                    )
+                ],
+            ),
+            ("", None),
+        )
+
+    def test_no_failures(self):
+        self.assertEqual(
+            _generate_report(
+                "Foo",
+                [
+                    junit_from_xml(
+                        dedent(
+                            """\
+          <?xml version="1.0" encoding="UTF-8"?>
+          <testsuites time="0.00">
+          <testsuite name="Passed" tests="1" failures="0" skipped="0" time="0.00">
+          <testcase classname="Bar/test_1" name="test_1" time="0.00"/>
+          </testsuite>
+          </testsuites>"""
+                        )
+                    )
+                ],
+            ),
+            (
+                dedent(
+                    """\
+              # Foo
+
+              * 1 test passed"""
+                ),
+                "success",
+            ),
+        )
+
+    def test_report_single_file_single_testsuite(self):
+        self.assertEqual(
+            _generate_report(
+                "Foo",
+                [
+                    junit_from_xml(
+                        dedent(
+                            """\
+          <?xml version="1.0" encoding="UTF-8"?>
+          <testsuites time="8.89">
+          <testsuite name="Bar" tests="4" failures="2" skipped="1" time="410.63">
+          <testcase classname="Bar/test_1" name="test_1" time="0.02"/>
+          <testcase classname="Bar/test_2" name="test_2" time="0.02">
+            <skipped message="Reason"/>
+          </testcase>
+          <testcase classname="Bar/test_3" name="test_3" time="0.02">
+            <failure><![CDATA[Output goes here]]></failure>
+          </testcase>
+          <testcase classname="Bar/test_4" name="test_4" time="0.02">
+            <failure><![CDATA[Other output goes here]]></failure>
+          </testcase>
+          </testsuite>
+          </testsuites>"""
+                        )
+                    )
+                ],
+            ),
+            (
+                dedent(
+                    """\
+          # Foo
+
+          * 1 test passed
+          * 1 test skipped
+          * 2 tests failed
+
+          ## Failed tests
+          (click to see output)
+
+          ### Bar
+          <details>
+          <summary>Bar/test_3/test_3</summary>
+
+          ```
+          Output goes here
+          ```
+          </details>
+          <details>
+          <summary>Bar/test_4/test_4</summary>
+
+          ```
+          Other output goes here
+          ```
+          </details>"""
+                ),
+                "error",
+            ),
+        )
+
+    MULTI_SUITE_OUTPUT = (
+        dedent(
+            """\
+        # ABC and DEF
+
+        * 1 test passed
+        * 1 test skipped
+        * 2 tests failed
+
+        ## Failed tests
+        (click to see output)
+
+        ### ABC
+        <details>
+        <summary>ABC/test_2/test_2</summary>
+
+        ```
+        ABC/test_2 output goes here
+        ```
+        </details>
+
+        ### DEF
+        <details>
+        <summary>DEF/test_2/test_2</summary>
+
+        ```
+        DEF/test_2 output goes here
+        ```
+        </details>"""
+        ),
+        "error",
+    )
+
+    def test_report_single_file_multiple_testsuites(self):
+        self.assertEqual(
+            _generate_report(
+                "ABC and DEF",
+                [
+                    junit_from_xml(
+                        dedent(
+                            """\
+          <?xml version="1.0" encoding="UTF-8"?>
+          <testsuites time="8.89">
+          <testsuite name="ABC" tests="2" failures="1" skipped="0" time="410.63">
+          <testcase classname="ABC/test_1" name="test_1" time="0.02"/>
+          <testcase classname="ABC/test_2" name="test_2" time="0.02">
+            <failure><![CDATA[ABC/test_2 output goes here]]></failure>
+          </testcase>
+          </testsuite>
+          <testsuite name="DEF" tests="2" failures="1" skipped="1" time="410.63">
+          <testcase classname="DEF/test_1" name="test_1" time="0.02">
+            <skipped message="reason"/>
+          </testcase>
+          <testcase classname="DEF/test_2" name="test_2" time="0.02">
+            <failure><![CDATA[DEF/test_2 output goes here]]></failure>
+          </testcase>
+          </testsuite>
+          </testsuites>"""
+                        )
+                    )
+                ],
+            ),
+            self.MULTI_SUITE_OUTPUT,
+        )
+
+    def test_report_multiple_files_multiple_testsuites(self):
+        self.assertEqual(
+            _generate_report(
+                "ABC and DEF",
+                [
+                    junit_from_xml(
+                        dedent(
+                            """\
+          <?xml version="1.0" encoding="UTF-8"?>
+          <testsuites time="8.89">
+          <testsuite name="ABC" tests="2" failures="1" skipped="0" time="410.63">
+          <testcase classname="ABC/test_1" name="test_1" time="0.02"/>
+          <testcase classname="ABC/test_2" name="test_2" time="0.02">
+            <failure><![CDATA[ABC/test_2 output goes here]]></failure>
+          </testcase>
+          </testsuite>
+          </testsuites>"""
+                        )
+                    ),
+                    junit_from_xml(
+                        dedent(
+                            """\
+          <?xml version="1.0" encoding="UTF-8"?>
+          <testsuites time="8.89">
+          <testsuite name="DEF" tests="2" failures="1" skipped="1" time="410.63">
+          <testcase classname="DEF/test_1" name="test_1" time="0.02">
+            <skipped message="reason"/>
+          </testcase>
+          <testcase classname="DEF/test_2" name="test_2" time="0.02">
+            <failure><![CDATA[DEF/test_2 output goes here]]></failure>
+          </testcase>
+          </testsuite>
+          </testsuites>"""
+                        )
+                    ),
+                ],
+            ),
+            self.MULTI_SUITE_OUTPUT,
+        )
+
+
+def _generate_report(title, junit_objects):
+    style = None
+
+    if not junit_objects:
+        return ("", style)
+
+    failures = {}
+    tests_run = 0
+    tests_skipped = 0
+    tests_failed = 0
+
+    for results in junit_objects:
+        for testsuite in results:
+            tests_run += testsuite.tests
+            tests_skipped += testsuite.skipped
+            tests_failed += testsuite.failures
+
+            for test in testsuite:
+                if (
+                    not test.is_passed
+                    and test.result
+                    and isinstance(test.result[0], Failure)
+                ):
+                    if failures.get(testsuite.name) is None:
+                        failures[testsuite.name] = []
+                    failures[testsuite.name].append(
+                        (test.classname + "/" + test.name, test.result[0].text)
+                    )
+
+    if not tests_run:
+        return ("", style)
+
+    style = "error" if tests_failed else "success"
+    report = [f"# {title}", ""]
+
+    tests_passed = tests_run - tests_skipped - tests_failed
+
+    def plural(num_tests):
+        return "test" if num_tests == 1 else "tests"
+
+    if tests_passed:
+        report.append(f"* {tests_passed} {plural(tests_passed)} passed")
+    if tests_skipped:
+        report.append(f"* {tests_skipped} {plural(tests_skipped)} skipped")
+    if tests_failed:
+        report.append(f"* {tests_failed} {plural(tests_failed)} failed")
+
+    if failures:
+        report.extend(["", "## Failed tests", "(click to see output)"])
+        for testsuite_name, failures in failures.items():
+            report.extend(["", f"### {testsuite_name}"])
+            for name, output in failures:
+                report.extend(
+                    [
+                        "<details>",
+                        f"<summary>{name}</summary>",
+                        "",
+                        "```",
+                        output,
+                        "```",
+                        "</details>",
+                    ]
+                )
+
+    return "\n".join(report), style
+
+
+def generate_report(title, junit_files):
+    return _generate_report(title, [JUnitXml.fromfile(p) for p in junit_files])
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "title", help="Title of the test report, without Markdown formatting."
+    )
+    parser.add_argument("context", help="Annotation context to write to.")
+    parser.add_argument("junit_files", help="Paths to JUnit report files.", nargs="*")
+    args = parser.parse_args()
+
+    report, style = generate_report(args.title, args.junit_files)
+    check_call(
+        [
+            "buildkite-agent",
+            "annotate",
+            "--context",
+            args.context,
+            "--style",
+            style,
+            report,
+        ]
+    )
diff --git a/.ci/monolithic-linux.sh b/.ci/monolithic-linux.sh
index b78dc59432b65..c9ad32a46e286 100755
--- a/.ci/monolithic-linux.sh
+++ b/.ci/monolithic-linux.sh
@@ -28,18 +28,47 @@ if [[ -n "${CLEAR_CACHE:-}" ]]; then
   ccache --clear
 fi
 
-function show-stats {
+function at-exit {
+  python3 "${MONOREPO_ROOT}"/.ci/generate_test_report.py ":linux: Linux x64 Test Results" \
+    "linux-x64-test-results" "${BUILD_DIR}"/*-test-results.xml
+
   mkdir -p artifacts
   ccache --print-stats > artifacts/ccache_stats.txt
 }
-trap show-stats EXIT
+trap at-exit EXIT
+
+# TODO: separate file for import into Windows script?
+function ninja-targets {
+  # $1 is the ninja arguments to use
+  # $2 is is an optional postfix to add to the target name when renaming result files.
+  # $3 is the list of targets
+  set +e
+  err_code=0
+  for target in $3; do
+    ninja $1 ${target}
+    new_err_code=$?
+    if [[ $new_err_code -ne 0 ]]; then
+      err_code=${new_err_code}
+    fi
+    mv "${BUILD_DIR}/test-results.xml" "${BUILD_DIR}/${target}${2}-test-results.xml"
+  done
+
+  if [[ $err_code -ne 0 ]]; then
+   exit $err_code
+  fi
+
+  set -e
+}
 
 projects="${1}"
 targets="${2}"
 
+lit_args="-v --xunit-xml-output ${BUILD_DIR}/test-results.xml --timeout=1200 --time-tests"
+
 echo "--- cmake"
 pip install -q -r "${MONOREPO_ROOT}"/mlir/python/requirements.txt
 pip install -q -r "${MONOREPO_ROOT}"/lldb/test/requirements.txt
+pip install -q junitparser==3.2.0
 cmake -S "${MONOREPO_ROOT}"/llvm -B "${BUILD_DIR}" \
       -D LLVM_ENABLE_PROJECTS="${projects}" \
       -G Ninja \
@@ -47,7 +76,7 @@ cmake -S "${MONOREPO_ROOT}"/llvm -B "${BUILD_DIR}" \
       -D LLVM_ENABLE_ASSERTIONS=ON \
       -D LLVM_BUILD_EXAMPLES=ON \
       -D COMPILER_RT_BUILD_LIBFUZZER=OFF \
-      -D LLVM_LIT_ARGS="-v --xunit-xml-output ${BUILD_DIR}/test-results.xml --timeout=1200 --time-tests" \
+      -D LLVM_LIT_ARGS="${lit_args}" \
       -D LLVM_ENABLE_LLD=ON \
       -D CMAKE_CXX_FLAGS=-gmlt \
       -D LLVM_CCACHE_BUILD=ON \
@@ -55,8 +84,8 @@ cmake -S "${MONOREPO_ROOT}"/llvm -B "${BUILD_DIR}" \
       -D CMAKE_INSTALL_PREFIX="${INSTALL_DIR}"
 
 echo "--- ninja"
-# Targets are not escaped as they are passed as separate arguments.
-ninja -C "${BUILD_DIR}" -k 0 ${targets}
+
+ninja-targets "-C "${BUILD_DIR}" -k 0" "" "$targets"
 
 runtimes="${3}"
 runtime_targets="${4}"
@@ -87,11 +116,14 @@ if [[ "${runtimes}" != "" ]]; then
       -D CMAKE_BUILD_TYPE=RelWithDebInfo \
       -D CMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
       -D LIBCXX_TEST_PARAMS="std=c++03" \
-      -D LIBCXXABI_TEST_PARAMS="std=c++03"
+      -D LIBCXXABI_TEST_PARAMS="std=c++03" \
+      -D LLVM_LIT_ARGS="${lit_args}"
 
   echo "--- ninja runtimes C++03"
 
-  ninja -vC "${RUNTIMES_BUILD_DIR}" ${runtime_targets}
+  # TODO: there's no way to tell a failure here apart from a failure of the same
+  # test in the other build mode.
+  ninja-targets "-vC "${RUNTIMES_BUILD_DIR}"" "-cxx03" "${runtime_targets}"
 
   echo "--- cmake runtimes C++26"
 
@@ -104,11 +136,12 @@ if [[ "${runtimes}" != "" ]]; then
       -D CMAKE_BUILD_TYPE=RelWithDebInfo \
       -D CMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
       -D LIBCXX_TEST_PARAMS="std=c++26" \
-      -D LIBCXXABI_TEST_PARAMS="std=c++26"
+      -D LIBCXXABI_TEST_PARAMS="std=c++26" \
+      -D LLVM_LIT_ARGS="${lit_args}"
 
   echo "--- ninja runtimes C++26"
 
-  ninja -vC "${RUNTIMES_BUILD_DIR}" ${runtime_targets}
+  ninja-targets "-vC "${RUNTIMES_BUILD_DIR}"" "-cxx26" "${runtime_targets}"
 
   echo "--- cmake runtimes clang modules"
 
@@ -121,9 +154,10 @@ if [[ "${runtimes}" != "" ]]; then
       -D CMAKE_BUILD_TYPE=RelWithDebInfo \
       -D CMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
       -D LIBCXX_TEST_PARAMS="enable_modules=clang" \
-      -D LIBCXXABI_TEST_PARAMS="enable_modules=clang"
+      -D LIBCXXABI_TEST_PARAMS="enable_modules=clang" \
+      -D LLVM_LIT_ARGS="${lit_args}"
 
   echo "--- ninja runtimes clang modules"
-  
-  ninja -vC "${RUNTIMES_BUILD_DIR}" ${runtime_targets}
+
+  ninja-targets "-vC "${RUNTIMES_BUILD_DIR}"" "-modules" "${runtime_targets}"
 fi
diff --git a/.ci/monolithic-windows.sh b/.ci/monolithic-windows.sh
index 91e719c52d436..daac89b4a632d 100755
--- a/.ci/monolithic-windows.sh
+++ b/.ci/monolithic-windows.sh
@@ -27,16 +27,20 @@ if [[ -n "${CLEAR_CACHE:-}" ]]; then
 fi
 
 sccache --zero-stats
-function show-stats {
+function at-exit {
+  python "${MONOREPO_ROOT}"/.ci/generate_test_report.py ":windows: Windows x64 Test Results" \
+    "windows-x64-test-results" "${BUILD_DIR}"/test-results*.xml
+
   mkdir -p artifacts
   sccache --show-stats >> artifacts/sccache_stats.txt
 }
-trap show-stats EXIT
+trap at-exit EXIT
 
 projects="${1}"
 targets="${2}"
 
 echo "--- cmake"
+pip install junitparser==3.2.0
 pip install -q -r "${MONOREPO_ROOT}"/mlir/python/requirements.txt
 
 # The CMAKE_*_LINKER_FLAGS to disable the manifest come from research
diff --git a/clang/README.md b/clang/README.md
index b98182d8a3f68..94b1e1a7a0743 100644
--- a/clang/README.md
+++ b/clang/README.md
@@ -23,3 +23,5 @@ If you're interested in more (including how to build Clang) it is best to read t
 * If you find a bug in Clang, please file it in the LLVM bug tracker:
   
     https://github.com/llvm/llvm-project/issues
+
+test change
\ No newline at end of file
diff --git a/clang/test/Driver/cl-pch.c b/clang/test/Driver/cl-pch.c
index 36d83a11242dc..1a9527458ebf4 100644
--- a/clang/test/Driver/cl-pch.c
+++ b/clang/test/Driver/cl-pch.c
@@ -25,7 +25,7 @@
 // CHECK-YCTP-SAME: -o
 // CHECK-YCTP-SAME: pchfile.pch
 // CHECK-YCTP-SAME: -x
-// CHECK-YCTP-SAME: c++-header
+// CHECK-YCTP-SAME: c++-header -- this will fail tests on windows!
 
 // Except if a later /TC changes it back.
 // RUN: %clang_cl -Werror /Yc%S/Inputs/pchfile.h /FI%S/Inputs/pchfile.h /c /Fo%t/pchfile.obj /Fp%t/pchfile.pch -v -- %s 2>&1 \
diff --git a/llvm/README.txt b/llvm/README.txt
index b9b71a3b6daff..ba60b8ffdd072 100644
--- a/llvm/README.txt
+++ b/llvm/README.txt
@@ -15,3 +15,5 @@ documentation setup.
 
 If you are writing a package for LLVM, see docs/Packaging.rst for our
 suggestions.
+
+test change
\ No newline at end of file