diff --git a/.github/workflows/tdiff.yml b/.github/workflows/tdiff.yml
new file mode 100644
index 0000000000000..63c6792d87a77
--- /dev/null
+++ b/.github/workflows/tdiff.yml
@@ -0,0 +1,123 @@
+name: Diff llvm-test-suite codegen
+
+on:
+  issue_comment:
+    types:
+      - created
+      - edited
+
+jobs:
+  tdiff:
+    name: Build and diff
+    runs-on: ubuntu-24.04
+    permissions:
+      issues: write
+      pull-requests: write
+    # if: >-
+    #   !startswith(github.event.comment.body, '<!--IGNORE-->') &&
+    #   github.event.issue.pull_request && contains(github.event.comment.body, '/tdiff')
+    steps:
+      - id: base-ref
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            const { data: pr } = await github.rest.pulls.get({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: context.payload.issue.number
+            });
+            core.setOutput('base_ref', pr.base.ref);
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+        with:
+          ref: refs/pull/${{ github.event.issue.number }}/head
+      - run: |
+          echo "REF=$(git rev-parse HEAD)" >> $GITHUB_ENV
+          echo "MERGE_BASE=$(git merge-base HEAD ${{steps.base-ref.outputs.base_ref}})" >> $GITHUB_ENV
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+        with:
+          repository: llvm/llvm-test-suite
+          path: llvm-test-suite
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y cmake ninja-build libc6-dev-{arm64,riscv64}-cross libgcc-14-dev-{arm64,riscv64}-cross libstdc++-14-dev-{arm64,riscv64}-cross 
+      - run: cmake -B build -DCMAKE_BUILD_TYPE=Release -DLLVM_TARGETS_TO_BUILD='AArch64;X86;RISCV' -DLLVM_ENABLE_PROJECTS='clang;lld' -DLLVM_APPEND_VC_REV=OFF llvm -GNinja
+      - run: ninja -C build
+      - run: |
+          cat << EOF > rva23u64.cmake
+          set(CMAKE_SYSTEM_NAME Linux) 
+          set(CMAKE_C_COMPILER ${GITHUB_WORKSPACE}/build/bin/clang)
+          set(CMAKE_CXX_COMPILER ${GITHUB_WORKSPACE}/build/bin/clang++)
+          set(CMAKE_C_COMPILER_TARGET riscv64-linux-gnu) 
+          set(CMAKE_CXX_COMPILER_TARGET riscv64-linux-gnu)
+          set(CMAKE_C_FLAGS_INIT "-march=rva23u64 -save-temps=obj")
+          set(CMAKE_CXX_FLAGS_INIT "-march=rva23u64 -save-temps=obj")
+          set(CMAKE_SYSTEM_PROCESSOR riscv64)
+          set(CMAKE_LINKER_TYPE LLD)          
+          EOF
+          cat << EOF > armv9-a.cmake
+          set(CMAKE_SYSTEM_NAME Linux) 
+          set(CMAKE_C_COMPILER ${GITHUB_WORKSPACE}/build/bin/clang)
+          set(CMAKE_CXX_COMPILER ${GITHUB_WORKSPACE}/build/bin/clang++)
+          set(CMAKE_C_COMPILER_TARGET aarch64-linux-gnu) 
+          set(CMAKE_CXX_COMPILER_TARGET aarch64-linux-gnu)
+          set(CMAKE_C_FLAGS_INIT "-march=armv9-a -save-temps=obj")
+          set(CMAKE_CXX_FLAGS_INIT "-march=armv9-a -save-temps=obj")
+          set(CMAKE_SYSTEM_PROCESSOR arm64)
+          set(CMAKE_LINKER_TYPE LLD)          
+          EOF
+          cat << EOF > x86_64.cmake
+          set(CMAKE_C_COMPILER ${GITHUB_WORKSPACE}/build/bin/clang)
+          set(CMAKE_CXX_COMPILER ${GITHUB_WORKSPACE}/build/bin/clang++)
+          set(CMAKE_C_FLAGS_INIT "-save-temps=obj")
+          set(CMAKE_CXX_FLAGS_INIT "-save-temps=obj")
+          set(CMAKE_LINKER_TYPE LLD)          
+          EOF
+          build_llvm_test_suite () {
+            cmake -B build.$1 -C cmake/caches/O3.cmake --toolchain $2 -DTEST_SUITE_BENCHMARKING_ONLY=ON -DTEST_SUITE_RUN_BENCHMARKS=OFF -GNinja
+            ninja -C build.$1
+            $GITHUB_WORKSPACE/build/bin/llvm-lit build.$1 -o results.$1.json
+          }
+          build_llvm_test_suite rva23u64-O3-b rva23u64.cmake
+          build_llvm_test_suite armv9-a-O3-b armv9-a.cmake
+          build_llvm_test_suite x86_64-O3-b x86_64.cmake
+        working-directory: llvm-test-suite
+      - run: git fetch --depth=1 origin $MERGE_BASE && git checkout $MERGE_BASE
+      - run: ninja -C build
+      - run: |
+          build_llvm_test_suite () {
+            cmake -B build.$1 -C cmake/caches/O3.cmake --toolchain $2 -DTEST_SUITE_BENCHMARKING_ONLY=ON -DTEST_SUITE_RUN_BENCHMARKS=OFF -GNinja
+            ninja -C build.$1
+            $GITHUB_WORKSPACE/build/bin/llvm-lit build.$1 -o results.$1.json
+          }
+          build_llvm_test_suite rva23u64-O3-a rva23u64.cmake
+          build_llvm_test_suite armv9-a-O3-a armv9-a.cmake
+          build_llvm_test_suite x86_64-O3-a x86_64.cmake
+        working-directory: llvm-test-suite
+      - run: |
+          mkdir diffs
+          ./utils/tdiff.py -a build.rva23u64-O3-a -b build.rva23u64-O3-b -s all > diffs/rva23u64-O3.diff || true
+          ./utils/tdiff.py -a build.armv9-a-O3-a -b build.armv9-a-O3-b -s all > diffs/armv9-a-O3.diff || true
+          ./utils/tdiff.py -a build.x86_64-O3-a -b build.x86_64-O3-b -s all > diffs/x86_64-O3.diff || true
+        working-directory: llvm-test-suite
+      - uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f #v7.0.0
+        id: upload-diffs
+        with:
+          name: diffs
+          path: llvm-test-suite/diffs
+      - uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f #v7.0.0
+        with:
+          name: results
+          path: llvm-test-suite/results*.json
+      - uses: actions/github-script@v7
+        env:
+          DIFF_URL: ${{ steps.upload-diffs.outputs.artifact-url }}
+        with:
+          script: |
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: process.env.DIFF_URL
+            })