Revert "[CMake] Remove custom ccache CMake logic"

This reverts commit 0fad18c.

We need bots to be updated first.

llvm/CMakeLists.txt

@@ -233,8 +233,38 @@ if (LLVM_ENABLE_PROJECTS_USED OR NOT LLVM_ENABLE_PROJECTS STREQUAL "")
 endif()
 unset(SHOULD_ENABLE_PROJECT)
 
-if(DEFINED LLVM_CCACHE_BUILD)
-	message(FATAL_ERROR "-DLLVM_CACHE_BUILD=ON is deprecated! Use to the following options instead:\n-DCMAKE_C_COMPILER_LAUNCHER=ccache -DCMAKE_CXX_COMPILER_LAUNCHER=ccache")
+# Build llvm with ccache if the package is present
+set(LLVM_CCACHE_BUILD OFF CACHE BOOL "Set to ON for a ccache enabled build")
+if(LLVM_CCACHE_BUILD)
+  find_program(CCACHE_PROGRAM ccache)
+  if(CCACHE_PROGRAM)
+    set(LLVM_CCACHE_MAXSIZE "" CACHE STRING "Size of ccache")
+    set(LLVM_CCACHE_DIR "" CACHE STRING "Directory to keep ccached data")
+    set(LLVM_CCACHE_PARAMS "CCACHE_CPP2=yes CCACHE_HASHDIR=yes"
+        CACHE STRING "Parameters to pass through to ccache")
+
+    if(NOT CMAKE_SYSTEM_NAME MATCHES "Windows")
+      set(CCACHE_PROGRAM "${LLVM_CCACHE_PARAMS} ${CCACHE_PROGRAM}")
+      if (LLVM_CCACHE_MAXSIZE)
+        set(CCACHE_PROGRAM "CCACHE_MAXSIZE=${LLVM_CCACHE_MAXSIZE} ${CCACHE_PROGRAM}")
+      endif()
+      if (LLVM_CCACHE_DIR)
+        set(CCACHE_PROGRAM "CCACHE_DIR=${LLVM_CCACHE_DIR} ${CCACHE_PROGRAM}")
+      endif()
+      set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ${CCACHE_PROGRAM})
+    else()
+      if(LLVM_CCACHE_MAXSIZE OR LLVM_CCACHE_DIR OR
+         NOT LLVM_CCACHE_PARAMS MATCHES "CCACHE_CPP2=yes CCACHE_HASHDIR=yes")
+        message(FATAL_ERROR "Ccache configuration through CMake is not supported on Windows. Please use environment variables.")
+      endif()
+      # RULE_LAUNCH_COMPILE should work with Ninja but currently has issues
+      # with cmd.exe and some MSVC tools other than cl.exe
+      set(CMAKE_C_COMPILER_LAUNCHER ${CCACHE_PROGRAM})
+      set(CMAKE_CXX_COMPILER_LAUNCHER ${CCACHE_PROGRAM})
+    endif()
+  else()
+    message(FATAL_ERROR "Unable to find the program ccache. Set LLVM_CCACHE_BUILD to OFF")
+  endif()
 endif()
 
 set(LLVM_EXTERNAL_PROJECT_BUILD_TOOL_ARGS "" CACHE STRING
@@ -250,8 +280,8 @@ if(LLVM_DEPENDENCY_DEBUGGING)
   if(NOT CMAKE_HOST_APPLE)
     message(FATAL_ERROR "Dependency debugging is only currently supported on Darwin hosts.")
   endif()
-  if(DEFINED CMAKE_CXX_COMPILER_LAUNCHER)
-    message(FATAL_ERROR "Cannot enable dependency debugging while using a compiler launcher like ccache.")
+  if(LLVM_CCACHE_BUILD)
+    message(FATAL_ERROR "Cannot enable dependency debugging while using ccache.")
   endif()
 endif()
 

llvm/docs/CMake.rst

@@ -402,6 +402,14 @@ enabled sub-projects. Nearly all of these variable names begin with
   example, you can build *llvm-as* with a Makefile-based system by executing *make
   llvm-as* at the root of your build directory.
 
+**LLVM_CCACHE_BUILD**:BOOL
+  If enabled and the ``ccache`` program is available, then LLVM will be
+  built using ``ccache`` to speed up rebuilds of LLVM and its components.
+  Defaults to OFF.  The size and location of the cache maintained
+  by ``ccache`` can be adjusted via the LLVM_CCACHE_MAXSIZE and LLVM_CCACHE_DIR
+  options, which are passed to the CCACHE_MAXSIZE and CCACHE_DIR environment
+  variables, respectively.
+
 **LLVM_CREATE_XCODE_TOOLCHAIN**:BOOL
   macOS Only: If enabled CMake will generate a target named
   'install-xcode-toolchain'. This target will create a directory at

llvm/docs/ReleaseNotes.rst

@@ -56,11 +56,6 @@ Changes to the LLVM IR
 Changes to building LLVM
 ------------------------
 
-* Removed ``LLVM_CCACHE_BUILD``, ``LLVM_CCACHE_MAXSIZE``, ``LLVM_CCACHE_DIR``
-  and ``LLVM_CCACHE_PARAMS`` CMake options. Upstream CMake supports setting
-  ``CMAKE_CXX_COMPILER_LAUNCHER=ccache`` since CMake 3.4 and should be used
-  instead.
-
 Changes to TableGen
 -------------------
 

mlir/utils/clang-tidy/README.md

@@ -35,8 +35,7 @@ $ cmake ../llvm \
   -DCMAKE_BUILD_TYPE=Release \
   -DLLVM_ENABLE_ASSERTIONS=ON \
   -DLLVM_TARGETS_TO_BUILD="Native;NVPTX;AMDGPU" \
-  -DCMAKE_C_COMPILER_LAUNCHER=ccache \
-  -DCMAKE_CXX_COMPILER_LAUNCHER=ccache \
+  -DLLVM_CCACHE_BUILD=ON \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_CXX_COMPILER=clang++ \
   -DLLVM_ENABLE_LLD=ON \