diff --git a/.github/workflows/rarearchs.yml b/.github/workflows/rarearchs.yml
index 5b799bb7..bd282d2e 100644
--- a/.github/workflows/rarearchs.yml
+++ b/.github/workflows/rarearchs.yml
@@ -22,47 +22,69 @@ jobs:
       (!contains(github.event.head_commit.message, 'skip all')) ||
       (!contains(github.event.head_commit.message, 'skip rarearchs')) ||
       contains(github.event.head_commit.message, 'only rarearchs')
-    name: ${{matrix.arch}}/c++${{matrix.std}}/${{matrix.bt}}
+    name: ${{matrix.arch}}/c++${{matrix.std}}/${{matrix.bt}}${{matrix.suffix}}
     continue-on-error: true
     runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:
         include:
-          - {std: 11, bt: Debug  , arch: aarch64, distro: ubuntu20.04}
-          - {std: 11, bt: Release, arch: aarch64, distro: ubuntu20.04}
-          - {std: 14, bt: Debug  , arch: aarch64, distro: ubuntu20.04}
-          - {std: 14, bt: Release, arch: aarch64, distro: ubuntu20.04}
-          - {std: 17, bt: Debug  , arch: aarch64, distro: ubuntu20.04}
-          - {std: 17, bt: Release, arch: aarch64, distro: ubuntu20.04}
+          #- {std: 11, bt: Release, arch: aarch64, distro: ubuntu20.04, suffix: .O0, cxxflags: ' -O0 '}
+          #- {std: 11, bt: Release, arch: aarch64, distro: ubuntu20.04, suffix: .O1, cxxflags: ' -O1 '}
+          #- {std: 11, bt: Release, arch: aarch64, distro: ubuntu20.04, suffix: .O2, cxxflags: ' -O2 '}
+          #- {std: 11, bt: Release, arch: aarch64, distro: ubuntu20.04, suffix: .O3, cxxflags: ' -O3 '}
+          #- {std: 11, bt: Release, arch: aarch64, distro: ubuntu20.04, suffix: .O2dbg, cxxflags: ' -O2 -g -DNDEBUG '}
+          #- {std: 11, bt: Debug  , arch: aarch64, distro: ubuntu20.04, suffix: }
+          #- {std: 11, bt: Release, arch: aarch64, distro: ubuntu20.04, suffix: }
+          #- {std: 14, bt: Debug  , arch: aarch64, distro: ubuntu20.04, suffix: }
+          #- {std: 14, bt: Release, arch: aarch64, distro: ubuntu20.04, suffix: }
+          #- {std: 17, bt: Debug  , arch: aarch64, distro: ubuntu20.04, suffix: }
+          #- {std: 17, bt: Release, arch: aarch64, distro: ubuntu20.04, suffix: }
           #
-          - {std: 11, bt: Debug  , arch: ppc64le, distro: ubuntu20.04}
-          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04}
-          - {std: 14, bt: Debug  , arch: ppc64le, distro: ubuntu20.04}
-          - {std: 14, bt: Release, arch: ppc64le, distro: ubuntu20.04}
-          - {std: 17, bt: Debug  , arch: ppc64le, distro: ubuntu20.04}
-          - {std: 17, bt: Release, arch: ppc64le, distro: ubuntu20.04}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O0       , cxxflags: ' -O0 '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O0NDEBUG , cxxflags: ' -O0 -DNDEBUG '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O0gNDEBUG, cxxflags: ' -O0 -DNDEBUG -g '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O1       , cxxflags: ' -O1 '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O1NDEBUG , cxxflags: ' -O1 -DNDEBUG '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O1gNDEBUG, cxxflags: ' -O1 -DNDEBUG -g '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O2       , cxxflags: ' -O2 '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O2NDEBUG , cxxflags: ' -O2 -DNDEBUG '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O2gNDEBUG, cxxflags: ' -O2 -DNDEBUG -g '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O3       , cxxflags: ' -O3 '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O3NDEBUG , cxxflags: ' -O3 -DNDEBUG '}
+          - {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: .O3gNDEBUG, cxxflags: ' -O3 -DNDEBUG -g '}
+          #- {std: 11, bt: Debug  , arch: ppc64le, distro: ubuntu20.04, suffix: }
+          #- {std: 11, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: }
+          #- {std: 14, bt: Debug  , arch: ppc64le, distro: ubuntu20.04, suffix: }
+          #- {std: 14, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: }
+          #- {std: 17, bt: Debug  , arch: ppc64le, distro: ubuntu20.04, suffix: }
+          #- {std: 17, bt: Release, arch: ppc64le, distro: ubuntu20.04, suffix: }
           #
-          - {std: 11, bt: Debug  , arch: s390x  , distro: ubuntu20.04}
-          - {std: 11, bt: Release, arch: s390x  , distro: ubuntu20.04}
-          - {std: 14, bt: Debug  , arch: s390x  , distro: ubuntu20.04}
-          - {std: 14, bt: Release, arch: s390x  , distro: ubuntu20.04}
-          - {std: 17, bt: Debug  , arch: s390x  , distro: ubuntu20.04}
-          - {std: 17, bt: Release, arch: s390x  , distro: ubuntu20.04}
+          #- {std: 11, bt: Release, arch: s390x  , distro: ubuntu20.04, suffix: .O0, cxxflags: ' -O0 '}
+          #- {std: 11, bt: Release, arch: s390x  , distro: ubuntu20.04, suffix: .O1, cxxflags: ' -O1 '}
+          #- {std: 11, bt: Release, arch: s390x  , distro: ubuntu20.04, suffix: .O2, cxxflags: ' -O2 '}
+          #- {std: 11, bt: Release, arch: s390x  , distro: ubuntu20.04, suffix: .O3, cxxflags: ' -O3 '}
+          #- {std: 11, bt: Release, arch: s390x  , distro: ubuntu20.04, suffix: .O2dbg, cxxflags: ' -O2 -g -DNDEBUG '}
+          #- {std: 11, bt: Debug  , arch: s390x  , distro: ubuntu20.04, suffix: }
+          #- {std: 11, bt: Release, arch: s390x  , distro: ubuntu20.04, suffix: }
+          #- {std: 14, bt: Debug  , arch: s390x  , distro: ubuntu20.04, suffix: }
+          #- {std: 14, bt: Release, arch: s390x  , distro: ubuntu20.04, suffix: }
+          #- {std: 17, bt: Debug  , arch: s390x  , distro: ubuntu20.04, suffix: }
+          #- {std: 17, bt: Release, arch: s390x  , distro: ubuntu20.04, suffix: }
           #
-          #- {std: 11, bt: Debug  , arch: armv6  , distro: bullseye}
-          #- {std: 11, bt: Release, arch: armv6  , distro: bullseye}
-          #- {std: 14, bt: Debug  , arch: armv6  , distro: bullseye}
-          #- {std: 14, bt: Release, arch: armv6  , distro: bullseye}
-          #- {std: 17, bt: Debug  , arch: armv6  , distro: bullseye}
-          #- {std: 17, bt: Release, arch: armv6  , distro: bullseye}
+          #- {std: 11, bt: Debug  , arch: armv6  , distro: bullseye, suffix: }
+          #- {std: 11, bt: Release, arch: armv6  , distro: bullseye, suffix: }
+          #- {std: 14, bt: Debug  , arch: armv6  , distro: bullseye, suffix: }
+          #- {std: 14, bt: Release, arch: armv6  , distro: bullseye, suffix: }
+          #- {std: 17, bt: Debug  , arch: armv6  , distro: bullseye, suffix: }
+          #- {std: 17, bt: Release, arch: armv6  , distro: bullseye, suffix: }
           #
-          #- {std: 11, bt: Debug  , arch: armv7  , distro: ubuntu20.04}
-          #- {std: 11, bt: Release, arch: armv7  , distro: ubuntu20.04}
-          #- {std: 14, bt: Debug  , arch: armv7  , distro: ubuntu20.04}
-          #- {std: 14, bt: Release, arch: armv7  , distro: ubuntu20.04}
-          #- {std: 17, bt: Debug  , arch: armv7  , distro: ubuntu20.04}
-          #- {std: 17, bt: Release, arch: armv7  , distro: ubuntu20.04}
+          #- {std: 11, bt: Debug  , arch: armv7  , distro: ubuntu20.04, suffix: }
+          #- {std: 11, bt: Release, arch: armv7  , distro: ubuntu20.04, suffix: }
+          #- {std: 14, bt: Debug  , arch: armv7  , distro: ubuntu20.04, suffix: }
+          #- {std: 14, bt: Release, arch: armv7  , distro: ubuntu20.04, suffix: }
+          #- {std: 17, bt: Debug  , arch: armv7  , distro: ubuntu20.04, suffix: }
+          #- {std: 17, bt: Release, arch: armv7  , distro: ubuntu20.04, suffix: }
     steps:
       - {name: checkout, uses: actions/checkout@v4, with: {submodules: recursive}}
       - name: test
@@ -95,29 +117,53 @@ jobs:
             cmake --version
             echo "install took $((SECONDS - start_time))"
           run: |
-            set -x
+            set -xe
             start_time=$SECONDS
             uname -a
             pwd
             ls -lFhp .
             #
+            # https://stackoverflow.com/questions/5470257/how-to-see-which-flags-march-native-will-activate
+            echo | c++ -O0 -Q -E -v - </dev/null 2>&1
+            echo | c++ -O0 -Q -c --help=optimizers --help=target
+            echo | c++ -O0 -dM -E - | sort
+            echo -----
+            echo | c++ -O1 -Q -E -v - </dev/null 2>&1
+            echo | c++ -O1 -Q -c --help=optimizers --help=target
+            echo | c++ -O1 -dM -E - | sort
+            echo -----
+            echo | c++ -O2 -Q -E -v - </dev/null 2>&1
+            echo | c++ -O2 -Q -c --help=optimizers --help=target
+            echo | c++ -O2 -dM -E - | sort
+            echo -----
+            echo | c++ -O3 -Q -E -v - </dev/null 2>&1
+            echo | c++ -O3 -Q -c --help=optimizers --help=target
+            echo | c++ -O3 -dM -E - | sort
+            echo =====
+            #
             bdir=build_${{matrix.arch}}_${{matrix.bt}}_${{matrix.std}}
             idir=install_${{matrix.arch}}_${{matrix.bt}}_${{matrix.std}}
             mkdir -p $bdir
             #
-            time cmake -S . -B $bdir \
-              -DCMAKE_INSTALL_PREFIX=$idir \
-              -DCMAKE_BUILD_TYPE=${{matrix.bt}} \
-              -DC4_CXX_STANDARD=${{matrix.std}} \
-              -DCXX_STANDARD=${{matrix.std}} \
-              -DRYML_DEV=ON \
-              -DRYML_TEST_SUITE=ON \
-              -DRYML_BUILD_BENCHMARKS=OFF \
-              -DRYML_SANITIZE=OFF \
-              -DRYML_LINT=OFF \
-              -DRYML_VALGRIND=OFF
+            cmd="cmake -S . -B $bdir \
+                  -DCMAKE_INSTALL_PREFIX=$idir \
+                  -DCMAKE_BUILD_TYPE=${{matrix.bt}} \
+                  -DC4_CXX_STANDARD=${{matrix.std}} \
+                  -DCXX_STANDARD=${{matrix.std}} \
+                  -DRYML_DEV=ON \
+                  -DRYML_TEST_SUITE=ON \
+                  -DRYML_BUILD_BENCHMARKS=OFF \
+                  -DRYML_SANITIZE=OFF \
+                  -DRYML_LINT=OFF \
+                  -DRYML_VALGRIND=OFF"
+            echo $cmd
+            if [ -z "${{matrix.cxxflags}}" ] ; then
+              time $cmd
+            else
+              time $cmd -DCMAKE_CXX_FLAGS_RELEASE:STRING="${{matrix.cxxflags}}"
+            fi
             #
-            time cmake --build $bdir -j 3 --target ryml-test-build
+            time cmake --build $bdir --verbose -j 4 --target ryml-test-build
             #
-            time cmake --build $bdir -j 3 --target ryml-test-run
+            time cmake --build $bdir --target ryml-test-run
             echo "run took $((SECONDS - start_time))"