diff --git a/libcxx/test/std/utilities/template.bitset/bitset.members/left_shift.pass.cpp b/libcxx/test/std/utilities/template.bitset/bitset.members/left_shift.pass.cpp
--- a/libcxx/test/std/utilities/template.bitset/bitset.members/left_shift.pass.cpp
+++ b/libcxx/test/std/utilities/template.bitset/bitset.members/left_shift.pass.cpp
@@ -12,9 +12,19 @@
 #include <cassert>
 #include <cstddef>
 #include <vector>
+#include <bitset>
+#include <string>
+#include <vector>
 
-#include "../bitset_test_cases.h"
-#include "test_macros.h"
+template <int N>
+std::vector<std::bitset<N> > get_test_cases();
+
+template <>
+inline std::vector<std::bitset<0> > get_test_cases<0>() {
+    std::vector<std::bitset<0> > cases;
+    cases.push_back(std::bitset<0>());
+    return cases;
+}
 
 template <std::size_t N>
 void test_left_shift() {
@@ -30,14 +40,5 @@
 
 int main(int, char**) {
     test_left_shift<0>();
-    test_left_shift<1>();
-    test_left_shift<31>();
-    test_left_shift<32>();
-    test_left_shift<33>();
-    test_left_shift<63>();
-    test_left_shift<64>();
-    test_left_shift<65>();
-    test_left_shift<1000>();
-
     return 0;
 }
diff --git a/libcxx/utils/ci/buildkite-pipeline.yml b/libcxx/utils/ci/buildkite-pipeline.yml
--- a/libcxx/utils/ci/buildkite-pipeline.yml
+++ b/libcxx/utils/ci/buildkite-pipeline.yml
@@ -18,285 +18,8 @@
 #
 
 steps:
-  #
-  # Light pre-commit tests for things like formatting or when people forget
-  # to update generated files.
-  #
-  - label: "Format"
-    command: "libcxx/utils/ci/run-buildbot check-format"
-    artifact_paths:
-      - "**/clang-format.patch"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    soft_fail:
-        - exit_status: 1
-
-  - label: "Generated output"
-    command: "libcxx/utils/ci/run-buildbot check-generated-output"
-    artifact_paths:
-      - "**/generated_output.patch"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  #
-  # General testing with the default configuration, under all the supported
-  # Standard modes, with Clang and GCC. This catches most issues upfront.
-  # The goal of this step is to catch most issues while being very fast.
-  #
-  - wait
-
-  - label: "C++03"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx03"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++11"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx11"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++14"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx14"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++17"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx17"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx20"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++2b"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "GCC/C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-gcc"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  #
-  # All other supported configurations of libc++.
-  #
-  - wait
-
-  - label: "-fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot generic-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Static libraries"
-    command: "libcxx/utils/ci/run-buildbot generic-static"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "ASAN"
-    command: "libcxx/utils/ci/run-buildbot generic-asan"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "TSAN"
-    command: "libcxx/utils/ci/run-buildbot generic-tsan"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "UBSAN"
-    command: "libcxx/utils/ci/run-buildbot generic-ubsan"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "With LLVM's libunwind"
-    command: "libcxx/utils/ci/run-buildbot generic-with_llvm_unwinder"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Single-threaded"
-    command: "libcxx/utils/ci/run-buildbot generic-singlethreaded"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No debug mode"
-    command: "libcxx/utils/ci/run-buildbot generic-no-debug"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No Filesystem"
-    command: "libcxx/utils/ci/run-buildbot generic-no-filesystem"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No random device"
-    command: "libcxx/utils/ci/run-buildbot generic-no-random_device"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No locale"
-    command: "libcxx/utils/ci/run-buildbot generic-no-localization"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Benchmarks"
-    command: "libcxx/utils/ci/run-buildbot benchmarks"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Documentation"
-    command: "libcxx/utils/ci/run-buildbot documentation"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Legacy standalone build"
-    command: "libcxx/utils/ci/run-buildbot legacy-standalone"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Unified standalone build"
-    command: "libcxx/utils/ci/run-buildbot unified-standalone"
+  - label: "Bisect"
+    command: "libcxx/utils/ci/do-bisect"
     artifact_paths:
       - "**/test-results.xml"
     agents:
@@ -305,157 +28,3 @@
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
-
-  - label: "Runtimes build"
-    command: "libcxx/utils/ci/run-buildbot runtimes-build"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Windows"
-    # TODO: The CI runner doesn't have bash in the path currently. Once it
-    # has that, remove the absolute path and just call 'bash' here.
-    command: "\"\\Program Files\\Git\\usr\\bin\\bash\" libcxx/utils/ci/run-buildbot generic-win"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "windows"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "MacOS C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx20"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders-macos"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  # Build with the configuration we use to generate libc++.dylib on Apple platforms
-  - label: "Apple system"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Apple system -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  # Test back-deployment to older Apple platforms
-  - label: "Apple back-deployment macosx10.9"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system-backdeployment-10.9"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos10.15" # TODO: For now, we're running the back-deployment tests for 10.9 on 10.15, because we don't have proper 10.9 machines
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Apple back-deployment macosx10.15"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system-backdeployment-10.15"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos10.15"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "AArch64"
-    command: "libcxx/utils/ci/run-buildbot aarch64"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "aarch64"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "AArch64 -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot aarch64-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "aarch64"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv8"
-    command: "libcxx/utils/ci/run-buildbot armv8"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv8 -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot armv8-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv7"
-    command: "libcxx/utils/ci/run-buildbot armv7"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l" # Compiling for v7, running on v8 hardware
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv7 -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot armv7-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l" # Compiling for v7, running on v8 hardware
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
diff --git a/libcxx/utils/ci/do-bisect b/libcxx/utils/ci/do-bisect
new file mode 100755
--- /dev/null
+++ b/libcxx/utils/ci/do-bisect
@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+#===----------------------------------------------------------------------===##
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+#===----------------------------------------------------------------------===##
+
+set -ex
+set -o pipefail
+
+MONOREPO_ROOT="$(git rev-parse --show-toplevel)"
+BUILD_DIR="${MONOREPO_ROOT}/build/runtimes-build"
+INSTALL_DIR="${BUILD_DIR}/install"
+
+export CC=clang
+export CXX=clang++
+
+rm -rf "${BUILD_DIR}"
+
+echo "--- Generating CMake"
+cmake -S "${MONOREPO_ROOT}/llvm" \
+      -B "${BUILD_DIR}" \
+      -GNinja \
+      -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+      -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
+      -DLLVM_ENABLE_PROJECTS="clang" \
+      -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
+      -DLLVM_RUNTIME_TARGETS="x86_64-unknown-linux-gnu"
+
+git bisect start -- "${MONOREPO_ROOT}/clang" "${MONOREPO_ROOT}/libcxx"
+git bisect bad
+git bisect good 167da6c9e826b9befc27b6f5a6c540f7f28b7d5a
+git bisect run "${MONOREPO_ROOT}/libcxx/utils/ci/repro"
diff --git a/libcxx/utils/ci/repro b/libcxx/utils/ci/repro
new file mode 100755
--- /dev/null
+++ b/libcxx/utils/ci/repro
@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+#===----------------------------------------------------------------------===##
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+#===----------------------------------------------------------------------===##
+
+set -ex
+set -o pipefail
+
+MONOREPO_ROOT="$(git rev-parse --show-toplevel)"
+BUILD_DIR="${MONOREPO_ROOT}/build/runtimes-build"
+INSTALL_DIR="${BUILD_DIR}/install"
+
+echo "+++ Installing the runtimes"
+ninja -C "${BUILD_DIR}" install-clang install-runtimes
+
+"${BUILD_DIR}/bin/clang++" "${MONOREPO_ROOT}/libcxx/test/std/utilities/template.bitset/bitset.members/left_shift.pass.cpp" -nostdinc++ -isystem "${INSTALL_DIR}/include/c++/v1" -std=c++2a -fsyntax-only
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -390,10 +390,9 @@
           -DLLVM_RUNTIME_TARGETS="x86_64-unknown-linux-gnu"
 
     echo "+++ Running the libc++ and libc++abi tests"
-    ${NINJA} -C "${BUILD_DIR}" check-runtimes
+    ${NINJA} -C "${BUILD_DIR}" install-runtimes
 
-    echo "--- Installing libc++ and libc++abi to a fake location"
-    ${NINJA} -C "${BUILD_DIR}" install-cxx install-cxxabi
+    "${BUILD_DIR}/bin/clang++" "${MONOREPO_ROOT}/libcxx/test/std/utilities/template.bitset/bitset.members/left_shift.pass.cpp" -std=c++2a -fsyntax-only
 ;;
 legacy-standalone)
     export CC=clang