Fix miscompilation / liveness errors for string operations (#3960)

Author: mshinwell

.github/workflows/build.yml

@@ -178,7 +178,6 @@ jobs:
     env:
       J: "3"
       run_testsuite: "true"
-      expected_fail: "${{matrix.expected_fail == true}}"
 
     steps:
     - name: Checkout the Flambda backend repo
@@ -200,12 +199,14 @@ jobs:
       if: matrix.os == 'macos-latest'
       run: HOMEBREW_NO_INSTALL_CLEANUP=TRUE brew install autoconf
 
+      # NB. The "rev" number in the cache key below must be updated each time
+      # the patch file is changed!
     - name: Cache OCaml 4.14, dune and menhir
       uses: actions/cache@v4
       id: cache
       with:
         path: ${{ github.workspace }}/ocaml-414/_install
-        key: ${{ matrix.os }}-cache-ocaml-414-patched-dune-3152-menhir-20231231
+        key: ${{ matrix.os }}-cache-ocaml-414-patched-dune-3152-menhir-20231231-rev13
 
     - name: Checkout OCaml 4.14
       uses: actions/checkout@master
@@ -285,14 +286,23 @@ jobs:
           --with-dune=$GITHUB_WORKSPACE/ocaml-414/_install/bin/dune \
           ${{ matrix.config }}
 
-    - name: Setup for saving core files (not for macOS at the moment)
+    - name: Setup for saving core files (not for macOS)
       if: matrix.os != 'macos-latest'
       run: |
         sudo mkdir /cores
         sudo chmod 777 /cores
         # Core filenames will be of the form executable.pid.timestamp:
         sudo bash -c 'echo "/cores/%e.%p.%t" > /proc/sys/kernel/core_pattern'
 
+    - name: Setup for saving core files (macOS)
+      if: matrix.os == 'macos-latest'
+      run: |
+        sudo chmod 1777 /cores
+        sudo sysctl kern.coredump=1
+        /usr/libexec/PlistBuddy -c "Add :com.apple.security.get-task-allow bool true" /tmp/core.entitlements
+        codesign -s - -f --entitlements /tmp/core.entitlements $GITHUB_WORKSPACE/ocaml-414/_install/bin/ocamlc.opt
+        codesign -s - -f --entitlements /tmp/core.entitlements $GITHUB_WORKSPACE/ocaml-414/_install/bin/ocamlopt.opt
+
     - name: Build, install and test Flambda backend
       working-directory: flambda_backend
       run: |
@@ -313,25 +323,35 @@ jobs:
       run: |
         PATH=$GITHUB_WORKSPACE/ocaml-414/_install/bin:$PATH make check_all_arches
 
-# CR-soon xclerc for xclerc: re-enable the "upload-artifact" action
-# (they are failing @4 because the names are not unique)
-#    - uses: actions/upload-artifact@v4
-#      if: ${{ failure() }} && matrix.os != 'macos-latest'
-#      with:
-#        name: cores-${{ github.sha }}
-#        path: /cores
-#
-#    - uses: actions/upload-artifact@v4
-#      if: ${{ failure() }} && matrix.os != 'macos-latest'
-#      with:
-#        name: _build-${{ github.sha }}
-#        path: $GITHUB_WORKSPACE/_build
+    - uses: actions/upload-artifact@v4
+      if: ${{ failure() }}
+      with:
+        name: cores-${{ github.sha }}-${{ github.run_id }}-${{ matrix.name }}
+        path: /cores
+
+#     - uses: actions/upload-artifact@v4
+#       if: ${{ failure() }}
+#       with:
+#         name: ocaml-414-${{ github.sha }}-${{ github.run_id }}-${{ matrix.name }}
+#         path: ${{ github.workspace }}/ocaml-414/_install
+
+    - uses: actions/upload-artifact@v4
+      if: ${{ failure() }} && matrix.os == 'macos-latest'
+      with:
+        name: DiagnosticReports-${{ github.sha }}-${{ github.run_id }}-${{ matrix.name }}
+        path: /Users/runner/Library/Logs/DiagnosticReports
+
+#     - uses: actions/upload-artifact@v4
+#       if: ${{ failure() }}
+#       with:
+#         name: _build-${{ github.sha }}-${{ github.run_id }}-${{ matrix.name }}
+#         path: ${{ github.workspace }}/flambda_backend/_build
 #
-#    - uses: actions/upload-artifact@v4
-#      if: ${{ failure() }} && matrix.os != 'macos-latest'
-#      with:
-#        name: _runtest-${{ github.sha }}
-#        path: $GITHUB_WORKSPACE/_runtest
+#     - uses: actions/upload-artifact@v4
+#       if: ${{ failure() }}
+#       with:
+#         name: _runtest-${{ github.sha }}-${{ github.run_id }}-${{ matrix.name }}
+#         path: ${{ github.workspace }}/flambda_backend/_runtest
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}