diff --git a/.buildbot/z13.sh b/.buildbot/z13.sh
index 2eebfd7..0ef81dc 100755
--- a/.buildbot/z13.sh
+++ b/.buildbot/z13.sh
@@ -25,6 +25,43 @@ export CPATH=${INSTALL_PATH}/include:${CPATH}
 export PATH=${JAVA_HOME}/bin:${PATH}
 export CLASSPATH=.:${JAVA_HOME}/lib:${JAVA_HOME}/lib/tools.jar:${CLASSPATH}
 
+# If LLVM_PROJECT_ROOT does not exist, or llvm-project commit hash changed,
+# (re)build llvm-project
+if ! [ -d ${LLVM_PROJECT_ROOT} ]; then
+    git clone https://github.com/llvm/llvm-project.git ${LLVM_PROJECT_ROOT}
+fi
+PREBUILT_LLVM_PROJECT_SHA1=$(git -C ${LLVM_PROJECT_ROOT} rev-parse HEAD)
+EXPECTED_LLVM_PROJECT_SHA1=$(cat utils/clone-mlir.sh|grep -Po '(?<=git checkout )[0-9a-f]+')
+
+echo "${LLVM_PROJECT_ROOT} sha1 prebuilt ${PREBUILT_LLVM_PROJECT_SHA1} expected ${EXPECTED_LLVM_PROJECT_SHA1}"
+
+if [ "$1" = "shared" ]; then
+    LLVM_BUILD_SHARED_LIBS=ON
+else
+    LLVM_BUILD_SHARED_LIBS=OFF
+fi
+
+if ! [ -d ${LLVM_PROJECT_ROOT}/build ] ||
+   [ "${PREBUILT_LLVM_PROJECT_SHA1}" != "${EXPECTED_LLVM_PROJECT_SHA1}" ]; then
+    echo "Rebuild llvm-project with sha1 ${EXPECTED_LLVM_PROJECT_SHA1}"
+    pushd ${LLVM_PROJECT_ROOT}
+    git fetch && git checkout ${EXPECTED_LLVM_PROJECT_SHA1}
+    rm -rf build && mkdir -p build && cd build
+    cmake -G Ninja ../llvm \
+	  -DLLVM_ENABLE_PROJECTS=mlir \
+	  -DLLVM_BUILD_EXAMPLES=ON \
+	  -DLLVM_TARGETS_TO_BUILD="host" \
+	  -DCMAKE_BUILD_TYPE=Release \
+	  -DLLVM_ENABLE_ASSERTIONS=ON \
+	  -DLLVM_ENABLE_RTTI=ON \
+	  -DBUILD_SHARED_LIBS=${LLVM_BUILD_SHARED_LIBS}
+    cmake --build . --target -- ${MAKEFLAGS}
+    popd
+else
+    echo "Rebuild llvm-project not needed"
+fi
+
+# Build ONNX MLIR against specified llvm-project
 export BUILD_PATH=build-against-$(basename ${LLVM_PROJECT_ROOT})
 mkdir ${BUILD_PATH} && cd ${BUILD_PATH}