diff --git a/.ci/compute_projects.py b/.ci/compute_projects.py
index c3cf714ce6c10..b22c8df8cf36a 100644
--- a/.ci/compute_projects.py
+++ b/.ci/compute_projects.py
@@ -19,6 +19,7 @@
 PROJECT_DEPENDENCIES = {
     "llvm": set(),
     "clang": {"llvm"},
+    "CIR": {"clang", "mlir"},
     "bolt": {"clang", "lld", "llvm"},
     "clang-tools-extra": {"clang", "llvm"},
     "compiler-rt": {"clang", "lld"},
@@ -55,6 +56,7 @@
     ".ci": {
         "llvm",
         "clang",
+        "CIR",
         "lld",
         "lldb",
         "bolt",
@@ -128,6 +130,7 @@
     "lldb": "check-lldb",
     "llvm": "check-llvm",
     "clang": "check-clang",
+    "CIR": "check-clang-cir",
     "bolt": "check-bolt",
     "lld": "check-lld",
     "flang": "check-flang",
@@ -192,7 +195,12 @@ def _compute_projects_to_test(modified_projects: Set[str], platform: str) -> Set
 def _compute_projects_to_build(
     projects_to_test: Set[str], runtimes: Set[str]
 ) -> Set[str]:
-    return _add_dependencies(projects_to_test, runtimes)
+    projects_with_deps = _add_dependencies(projects_to_test, runtimes)
+    # CIR is used as a pseudo-project in this script. We detect modifications
+    # to clang's CIR-specific subdirectories and add CIR as a modified project
+    # if a file in these directories is modified, but we need to remove it
+    # explicitly here.
+    return projects_with_deps - {"CIR"}
 
 
 def _compute_project_check_targets(projects_to_test: Set[str]) -> Set[str]:
@@ -247,6 +255,15 @@ def _get_modified_projects(modified_files: list[str]) -> Set[str]:
         # capacity.
         if len(path_parts) > 3 and path_parts[:3] == ("llvm", "utils", "gn"):
             continue
+        # If the file is in the clang/lib/CIR directory, add the CIR project.
+        if len(path_parts) > 3 and (
+            path_parts[:3] == ("clang", "lib", "CIR")
+            or path_parts[:3] == ("clang", "test", "CIR")
+            or path_parts[:4] == ("clang", "include", "clang", "CIR")
+        ):
+            modified_projects.add("clang")
+            modified_projects.add("CIR")
+            continue
         modified_projects.add(pathlib.Path(modified_file).parts[0])
     return modified_projects
 
@@ -267,6 +284,12 @@ def get_env_variables(modified_files: list[str], platform: str) -> Set[str]:
     runtimes_check_targets_needs_reconfig = _compute_project_check_targets(
         runtimes_to_test_needs_reconfig
     )
+
+    # Check if both clang and mlir are in projects_to_build to enable CIR
+    enable_cir = (
+        "ON" if "clang" in projects_to_build and "mlir" in projects_to_build else "OFF"
+    )
+
     # We use a semicolon to separate the projects/runtimes as they get passed
     # to the CMake invocation and thus we need to use the CMake list separator
     # (;). We use spaces to separate the check targets as they end up getting
@@ -279,6 +302,7 @@ def get_env_variables(modified_files: list[str], platform: str) -> Set[str]:
         "runtimes_check_targets_needs_reconfig": " ".join(
             sorted(runtimes_check_targets_needs_reconfig)
         ),
+        "enable_cir": enable_cir,
     }
 
 
diff --git a/.ci/compute_projects_test.py b/.ci/compute_projects_test.py
index 6299931e1ec34..07944dfe28359 100644
--- a/.ci/compute_projects_test.py
+++ b/.ci/compute_projects_test.py
@@ -104,6 +104,10 @@ def test_clang(self):
             env_variables["runtimes_check_targets_needs_reconfig"],
             "check-cxx check-cxxabi check-unwind",
         )
+        self.assertEqual(
+            env_variables["enable_cir"],
+            "OFF",
+        )
 
     def test_clang_windows(self):
         env_variables = compute_projects.get_env_variables(
@@ -126,6 +130,32 @@ def test_clang_windows(self):
             env_variables["runtimes_check_targets_needs_reconfig"],
             "check-cxx check-cxxabi check-unwind",
         )
+        self.assertEqual(env_variables["enable_cir"], "OFF")
+
+    def test_cir(self):
+        env_variables = compute_projects.get_env_variables(
+            ["clang/lib/CIR/CMakeLists.txt"], "Linux"
+        )
+        self.assertEqual(
+            env_variables["projects_to_build"],
+            "clang;clang-tools-extra;lld;llvm;mlir",
+        )
+        self.assertEqual(
+            env_variables["project_check_targets"],
+            "check-clang check-clang-cir check-clang-tools",
+        )
+        self.assertEqual(
+            env_variables["runtimes_to_build"], "compiler-rt;libcxx;libcxxabi;libunwind"
+        )
+        self.assertEqual(
+            env_variables["runtimes_check_targets"],
+            "check-compiler-rt",
+        )
+        self.assertEqual(
+            env_variables["runtimes_check_targets_needs_reconfig"],
+            "check-cxx check-cxxabi check-unwind",
+        )
+        self.assertEqual(env_variables["enable_cir"], "ON")
 
     def test_bolt(self):
         env_variables = compute_projects.get_env_variables(
@@ -153,11 +183,13 @@ def test_mlir(self):
         )
         self.assertEqual(env_variables["projects_to_build"], "clang;flang;llvm;mlir")
         self.assertEqual(
-            env_variables["project_check_targets"], "check-flang check-mlir"
+            env_variables["project_check_targets"],
+            "check-flang check-mlir",
         )
         self.assertEqual(env_variables["runtimes_to_build"], "")
         self.assertEqual(env_variables["runtimes_check_targets"], "")
         self.assertEqual(env_variables["runtimes_check_targets_needs_reconfig"], "")
+        self.assertEqual(env_variables["enable_cir"], "ON")
 
     def test_flang(self):
         env_variables = compute_projects.get_env_variables(
@@ -168,6 +200,7 @@ def test_flang(self):
         self.assertEqual(env_variables["runtimes_to_build"], "")
         self.assertEqual(env_variables["runtimes_check_targets"], "")
         self.assertEqual(env_variables["runtimes_check_targets_needs_reconfig"], "")
+        self.assertEqual(env_variables["enable_cir"], "OFF")
 
     def test_invalid_subproject(self):
         env_variables = compute_projects.get_env_variables(
@@ -237,7 +270,7 @@ def test_ci(self):
         )
         self.assertEqual(
             env_variables["project_check_targets"],
-            "check-bolt check-clang check-clang-tools check-flang check-lld check-lldb check-llvm check-mlir check-polly",
+            "check-bolt check-clang check-clang-cir check-clang-tools check-flang check-lld check-lldb check-llvm check-mlir check-polly",
         )
         self.assertEqual(
             env_variables["runtimes_to_build"],
diff --git a/.ci/monolithic-linux.sh b/.ci/monolithic-linux.sh
index 8d1faab13986c..0d35becdd8c8f 100755
--- a/.ci/monolithic-linux.sh
+++ b/.ci/monolithic-linux.sh
@@ -53,6 +53,7 @@ targets="${2}"
 runtimes="${3}"
 runtime_targets="${4}"
 runtime_targets_needs_reconfig="${5}"
+enable_cir="${6}"
 
 lit_args="-v --xunit-xml-output ${BUILD_DIR}/test-results.xml --use-unique-output-file-name --timeout=1200 --time-tests"
 
@@ -72,6 +73,7 @@ cmake -S "${MONOREPO_ROOT}"/llvm -B "${BUILD_DIR}" \
       -G Ninja \
       -D CMAKE_PREFIX_PATH="${HOME}/.local" \
       -D CMAKE_BUILD_TYPE=Release \
+      -D CLANG_ENABLE_CIR=${enable_cir} \
       -D LLVM_ENABLE_ASSERTIONS=ON \
       -D LLVM_BUILD_EXAMPLES=ON \
       -D COMPILER_RT_BUILD_LIBFUZZER=OFF \
diff --git a/.github/workflows/premerge.yaml b/.github/workflows/premerge.yaml
index 4435a3e905768..6ccc9f607ccf7 100644
--- a/.github/workflows/premerge.yaml
+++ b/.github/workflows/premerge.yaml
@@ -61,7 +61,7 @@ jobs:
           export CC=/opt/llvm/bin/clang
           export CXX=/opt/llvm/bin/clang++
 
-          ./.ci/monolithic-linux.sh "${projects_to_build}" "${project_check_targets}" "${runtimes_to_build}" "${runtimes_check_targets}" "${runtimes_check_targets_needs_reconfig}"
+          ./.ci/monolithic-linux.sh "${projects_to_build}" "${project_check_targets}" "${runtimes_to_build}" "${runtimes_check_targets}" "${runtimes_check_targets_needs_reconfig}" "${enable_cir}"
       - name: Upload Artifacts
         uses: actions/upload-artifact@65c4c4a1ddee5b72f698fdd19549f0f0fb45cf08 # v4.6.0
         with: