[Comgr][Cache] Disable the cache by default

Author: jmmartinez

amd/comgr/README.md

@@ -120,11 +120,15 @@ and eviction policy can be manipulated through specific environment variables.
 If an issue arises during cache initialization, the execution will proceed with
 the cache turned off.
 
+By default, the cache is turned off, set the environment variable
+`AMD_COMGR_CACHE=1` to enable it. This may change in a future release.
+
+* `AMD_COMGR_CACHE`: When unset or set to 0, the cache is turned off.
 * `AMD_COMGR_CACHE_DIR`: When set to "", the cache is turned off. If assigned a
   value, that value is used as the path for cache storage. By default, it is
   directed to "$XDG_CACHE_HOME/comgr_cache" (which defaults to
   "$USER/.cache/comgr_cache" on Linux, and "%LOCALAPPDATA%\cache\comgr_cache"
-  on Windows).
+  on Microsoft Windows).
 * `AMD_COMGR_CACHE_POLICY`: If assigned a value, the string is interpreted and
   applied to the cache pruning policy. The cache is pruned only upon program
   termination. The string format aligns with [Clang's ThinLTO cache pruning policy](https://clang.llvm.org/docs/ThinLTO.html#cache-pruning).

amd/comgr/src/comgr-env.cpp

@@ -81,6 +81,13 @@ StringRef getCachePolicy() {
 }
 
 StringRef getCacheDirectory() {
+  // By default the cache is deactivated. We hope to remove this variable in the
+  // future.
+  static const char *Enable = std::getenv("AMD_COMGR_CACHE");
+  bool CacheDisabled = !Enable || StringRef(Enable) == "0";
+  if (CacheDisabled)
+    return "";
+
   static const char *EnvCacheDirectory = std::getenv("AMD_COMGR_CACHE_DIR");
   if (EnvCacheDirectory)
     return EnvCacheDirectory;

amd/comgr/test-lit/compile-minimal-test-cached-bad-dir.cl

@@ -1,3 +1,5 @@
+// RUN: export AMD_COMGR_CACHE=1
+//
 // COM: fail to create the cache, but still produce something valid
 // RUN: rm -f %t.log
 // RUN: echo "not a directory" >  %t.txt

amd/comgr/test-lit/compile-minimal-test-cached-bad-policy.cl

@@ -1,3 +1,5 @@
+// RUN: export AMD_COMGR_CACHE=1
+//
 // COM: fail to create the cache, but still produce something valid
 // RUN: rm -f %t_log
 // RUN: AMD_COMGR_CACHE_DIR=%t.cache \

amd/comgr/test-lit/compile-minimal-test-cached.cl

@@ -1,8 +1,20 @@
 // RUN: rm -fr %t.cache
 //
+// RUN: unset AMD_COMGR_CACHE
+// RUN: AMD_COMGR_CACHE_DIR=%t.cache compile-minimal-test %S/compile-minimal-test.cl %t.bin
+// RUN: llvm-objdump -d %t.bin | FileCheck %S/compile-minimal-test.cl
+// RUN: [ ! -d %t.cache ]
+//
+// RUN: export AMD_COMGR_CACHE=0
+// RUN: AMD_COMGR_CACHE_DIR=%t.cache compile-minimal-test %S/compile-minimal-test.cl %t.bin
+// RUN: llvm-objdump -d %t.bin | FileCheck %S/compile-minimal-test.cl
+// RUN: [ ! -d %t.cache ]
+//
+// RUN: export AMD_COMGR_CACHE=1
+//
 // COM: run once and check that the cache directory exists and it has more than 1 element (one for the cache tag, one or more for the cached commands)
 // RUN: AMD_COMGR_CACHE_DIR=%t.cache compile-minimal-test %S/compile-minimal-test.cl %t_a.bin
-// RUN: llvm-objdump -d %t_a.bin | FileCheck %S/compile-minimal-test.cl 
+// RUN: llvm-objdump -d %t_a.bin | FileCheck %S/compile-minimal-test.cl
 // RUN: COUNT_BEFORE=$(ls "%t.cache" | wc -l)
 // COM: One element for the tag, one for bc->obj another for obj->exec. No elements for src->bc since we currently not support it.
 // RUN: [ 3 -eq $COUNT_BEFORE ] 
@@ -11,3 +23,4 @@
 // RUN: llvm-objdump -d %t_b.bin | FileCheck %S/compile-minimal-test.cl
 // RUN: COUNT_AFTER=$(ls "%t.cache" | wc -l)
 // RUN: [ $COUNT_AFTER = $COUNT_BEFORE ]
+//