Add local read/write variables, adjust comments.

.github/workflows/ci.yml

@@ -171,7 +171,7 @@ jobs:
     steps:
       - name: "Checking out repository"
         uses: actions/checkout@e2f20e631ae6d7dd3b768f56a5d2af784dd54791 # v2.5.0
-      # Restore caches.
+      # Restore caches unconditionally. Cache misses are okay.
       - name: "Fetching cache (git submodules)"
         uses: actions/cache/restore@58c146cc91c5b9e778e71775dfe9bf1442ad9a12 # v3.2.3
         with:
@@ -184,7 +184,8 @@ jobs:
           path: ${{ github.workspace }}/.ccache
           key: ccache_all_windows_${{ github.sha }}
           restore-keys: ccache_all_windows
-      # Fetch deps.
+      # Fetch dependencies.
+      # TODO(scotttodd): Move these into a Docker image.
       - name: "Updating git submodules"
         run: git submodule update --init --jobs 8 --depth 1
       - name: "Setting up Python"
@@ -203,8 +204,10 @@ jobs:
       # Finally: build and run tests.
       - name: "Building IREE"
         env:
-          IREE_USE_LOCAL_CCACHE: 1
           IREE_READ_REMOTE_CCACHE: 0
+          IREE_WRITE_REMOTE_CCACHE: 0
+          IREE_READ_LOCAL_CCACHE: 1
+          IREE_WRITE_LOCAL_CCACHE: ${{ needs.setup.outputs.write-caches }}
           CCACHE_DIR: ${{ github.workspace }}/.ccache
         run: ./build_tools/cmake/build_all.sh "${BUILD_DIR}"
       - name: "Testing IREE"

build_tools/cmake/setup_ccache.sh

@@ -13,9 +13,9 @@
 # Local caches can also be used to interface with external remote caches
 # (like https://github.com/actions/cache) by
 #   1. downloading the cache directory
-#   2. sourcing this file with IREE_USE_LOCAL_CCACHE=1 IREE_READ_REMOTE_CCACHE=0
+#   2. sourcing with IREE_READ_LOCAL_CCACHE=1 IREE_WRITE_LOCAL_CCACHE=[0,1]
 #   3. building with CMake
-#   4. uploading the cache directory (optionally)
+#   4. uploading the cache directory (if writing)
 #
 # Note: this file must be *sourced* not executed.
 
@@ -24,18 +24,19 @@ set -euo pipefail
 # Configuration environment variables.
 IREE_READ_REMOTE_CCACHE="${IREE_READ_REMOTE_CCACHE:-1}"
 IREE_WRITE_REMOTE_CCACHE="${IREE_WRITE_REMOTE_CCACHE:-0}"
-IREE_USE_LOCAL_CCACHE="${IREE_USE_LOCAL_CCACHE:-0}"
+IREE_READ_LOCAL_CCACHE="${IREE_READ_LOCAL_CCACHE:-0}"
+IREE_WRITE_LOCAL_CCACHE="${IREE_WRITE_LOCAL_CCACHE:-0}"
 
 if (( ${IREE_WRITE_REMOTE_CCACHE} == 1 && ${IREE_READ_REMOTE_CCACHE} != 1 )); then
   echo "Can't have 'IREE_WRITE_REMOTE_CCACHE' (${IREE_WRITE_REMOTE_CCACHE})" \
        " set without 'IREE_READ_REMOTE_CCACHE' (${IREE_READ_REMOTE_CCACHE})"
 fi
-if (( ${IREE_USE_LOCAL_CCACHE} == 1 && ${IREE_READ_REMOTE_CCACHE} == 1)); then
-  echo "Can't have 'IREE_USE_LOCAL_CCACHE' (${IREE_USE_LOCAL_CCACHE})" \
-       " set with 'IREE_READ_REMOTE_CCACHE' (${IREE_READ_REMOTE_CCACHE})"
+if (( ${IREE_WRITE_LOCAL_CCACHE} == 1 && ${IREE_READ_LOCAL_CCACHE} != 1 )); then
+  echo "Can't have 'IREE_WRITE_LOCAL_CCACHE' (${IREE_WRITE_LOCAL_CCACHE})" \
+       " set without 'IREE_READ_LOCAL_CCACHE' (${IREE_READ_LOCAL_CCACHE})"
 fi
 
-if (( IREE_READ_REMOTE_CCACHE == 1 || IREE_USE_LOCAL_CCACHE == 1 )); then
+if (( IREE_READ_REMOTE_CCACHE == 1 || IREE_READ_LOCAL_CCACHE == 1 )); then
   export IREE_USE_CCACHE=1
   export CMAKE_C_COMPILER_LAUNCHER=$(which ccache)
   export CMAKE_CXX_COMPILER_LAUNCHER=$(which ccache)
@@ -44,9 +45,16 @@ else
   export IREE_USE_CCACHE=0
 fi
 
+if (( IREE_READ_LOCAL_CCACHE == 1 && IREE_WRITE_LOCAL_CCACHE == 0 )); then
+  export CCACHE_READONLY=1
+fi
+
+if (( IREE_READ_REMOTE_CCACHE == 1 && IREE_READ_LOCAL_CCACHE == 0 )); then
+  export CCACHE_REMOTE_ONLY=1
+fi
+
 if (( IREE_READ_REMOTE_CCACHE == 1 )); then
   export CCACHE_REMOTE_STORAGE="http://storage.googleapis.com/iree-sccache/ccache"
-  export CCACHE_REMOTE_ONLY=1
   if (( IREE_WRITE_REMOTE_CCACHE == 1 )); then
     set +x # Don't leak the token (even though it's short-lived)
     export CCACHE_REMOTE_STORAGE="${CCACHE_REMOTE_STORAGE}|bearer-token=${IREE_CCACHE_GCP_TOKEN}"