[COMGR][Cache] Add environment variables AMD_COMGR_CACHE_DIR and AMD_COMGR_CACHE_POLICY

Set the AMD_COMGR_CACHE_DIR variable to "" during tests.

co-authored by anjenner and jmmartinez

Change-Id: I3a3aa7e734805bd78542f38c1779f85a9d695f20

Author: jmmartinez

amd/comgr/README.md

@@ -114,6 +114,22 @@ Comgr supports an environment variable to help locate LLVM:
   installation, which is currently used to locate the clang resource directory
   and clang binary path, allowing for additional optimizations.
 
+Comgr utilizes a cache to preserve the results of compilations between executions.
+The cache's status (enabled/disabled), storage location for its results,
+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.
+
+* `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).
+* `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).
+  The default policy is set as: "prune_interval=1h:prune_expiration=0h:cache_size=75%:cache_size_bytes=30g:cache_size_files=0".
+
 Comgr also supports some environment variables to aid in debugging. These
 include:
 

amd/comgr/src/comgr-env.cpp

@@ -37,10 +37,6 @@
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
-#include <fstream>
-#include <memory>
-#include <stdlib.h>
-
 using namespace llvm;
 
 namespace COMGR {
@@ -79,5 +75,28 @@ llvm::StringRef getLLVMPath() {
   return EnvLLVMPath;
 }
 
+StringRef getCachePolicy() {
+  static const char *EnvCachePolicy = std::getenv("AMD_COMGR_CACHE_POLICY");
+  return EnvCachePolicy;
+}
+
+StringRef getCacheDirectory() {
+  static const char *EnvCacheDirectory = std::getenv("AMD_COMGR_CACHE_DIR");
+  if (EnvCacheDirectory)
+    return EnvCacheDirectory;
+
+  // mark Result as static to keep it cached across calls
+  static SmallString<256> Result;
+  if (!Result.empty())
+    return Result;
+
+  if (sys::path::cache_directory(Result)) {
+    sys::path::append(Result, Twine("comgr_cache"));
+    return Result;
+  }
+
+  return "";
+}
+
 } // namespace env
 } // namespace COMGR

amd/comgr/src/comgr-env.h

@@ -59,6 +59,15 @@ bool needTimeStatistics();
 /// otherwise return the default LLVM path.
 llvm::StringRef getLLVMPath();
 
+/// If environment variable AMD_COMGR_CACHE_POLICY is set, return the
+/// environment variable, otherwise return empty
+llvm::StringRef getCachePolicy();
+
+/// If environment variable AMD_COMGR_CACHE_DIR is set, return the environment
+/// variable, otherwise return the default path: On Linux it's typically
+/// $HOME/.cache/comgr_cache (depends on XDG_CACHE_HOME)
+llvm::StringRef getCacheDirectory();
+
 } // namespace env
 } // namespace COMGR
 

amd/comgr/test-lit/lit.cfg.py

@@ -14,3 +14,7 @@
 
 if not config.comgr_disable_spirv:
     config.available_features.add("comgr-has-spirv")
+
+# By default, disable the cache for the tests.
+# Test for the cache must explicitly enable this variable.
+config.environment['AMD_COMGR_CACHE_DIR'] = ""

amd/comgr/test/CMakeLists.txt

@@ -193,9 +193,12 @@ endif()
   add_dependencies(check-comgr ${name})
   # Windows binaries have no equivalent to RPATH, so we must set their PATH to
   # include the .lib/.dll directory.
-  if (NOT(UNIX))
+  if (UNIX)
     set_tests_properties(${test_name}
-      PROPERTIES ENVIRONMENT "PATH=$<TARGET_LINKER_FILE_DIR:amd_comgr>")
+      PROPERTIES ENVIRONMENT "AMD_COMGR_CACHE_DIR=;")
+  else()
+    set_tests_properties(${test_name}
+      PROPERTIES ENVIRONMENT "PATH=$<TARGET_LINKER_FILE_DIR:amd_comgr>;AMD_COMGR_CACHE_DIR=;")
   endif()
 endmacro()