Remove sccache (#5206)

* Remove sccache

* CI docs

Author: expipiplus1

.github/actions/common-setup/action.yml

@@ -126,15 +126,6 @@ runs:
         path: ${{ github.workspace }}/build/llvm-project-install
         key: ${{ steps.cache-llvm.outputs.cache-primary-key }}
 
-
-    # Run this after building llvm, it's pointless to fill the caches with
-    # infrequent llvm build products
-    - name: Set up sccache
-      uses: mozilla-actions/sccache-action@v0.0.6
-      # Opportunistically use sccache, it's not available for example on self
-      # hosted runners or ARM
-      continue-on-error: true
-
     - name: Set environment variable for CMake and sccache
       shell: bash
       run: |
@@ -145,7 +136,6 @@ runs:
 
         # Set CMake to use sccache if it's available
         if command -v sccache; then
-          echo "SCCACHE_GHA_ENABLED=true" >> "$GITHUB_ENV"
           echo "CMAKE_CXX_COMPILER_LAUNCHER=sccache" >> "$GITHUB_ENV"
           echo "CMAKE_C_COMPILER_LAUNCHER=sccache" >> "$GITHUB_ENV"
         fi

docs/ci.md

@@ -1,18 +1,36 @@
 # Our CI
 
-There are github actions for testing building and testing slang.
+There are github actions for building and testing slang.
 
 ## Tests
 
-Most configurations run a restricted set of tests, however on some self hosted runners we run the full test suite, as well as running Falcor's test suite with the new slang build.
+Most configurations run a restricted set of tests, however on some self hosted
+runners we run the full test suite, as well as running Falcor's test suite with
+the new slang build.
 
 ## Building LLVM
 
-We require a static build of LLVM for building slang-llvm, we build and cache this in all workflow runs. Since this changes infrequently, the cache is almost always hit. A cold build takes about an hour on the slowest platform. The cached output is a few hundred MB, so conceivably if we add many more platforms we might be caching more than the 10GB github allowance, which would necessitate being a bit more complicated in building and tracking outputs here.
+We require a static build of LLVM for building slang-llvm, we build and cache
+this in all workflow runs. Since this changes infrequently, the cache is almost
+always hit. A cold build takes about an hour on the slowest platform. The
+cached output is a few hundred MB, so conceivably if we add many more platforms
+we might be caching more than the 10GB github allowance, which would
+necessitate being a bit more complicated in building and tracking outputs here.
 
-For slang-llvm, this is handled the same as any other dependency, except on Windows Debug builds, where we are required by the differences in Debug/Release standard libraries to always make a release build, this is noted in the ci action yaml file.
+For slang-llvm, this is handled the same as any other dependency, except on
+Windows Debug builds, where we are required by the differences in Debug/Release
+standard libraries to always make a release build, this is noted in the ci
+action yaml file.
+
+Note that we don't use sccache while building LLVM, as it changes very
+infrequently. The caching of LLVM is done by caching the final build product
+only.
 
 ## sccache
 
-The CI actions use sccache, keyed on compiler and platform, this runs on all configurations and significantly speeds up small source change builds. This cache can be safely missed without a large impact on build times.
+> Due to reliability issues, we are not currently using sccache, this is
+> historical/aspirational.
 
+The CI actions use sccache, keyed on compiler and platform, this runs on all
+configurations and significantly speeds up small source change builds. This
+cache can be safely missed without a large impact on build times.