Add Halide_CCACHE_BUILD option for CMake (#5804)

* Add Halide_CCACHE_BUILD option for CMake This replicates the approach LLVM already has of baking a use-cache option directly into the CMake options, without having to futz with changing CC/CXX/etc. * Update CMakeLists.txt * Add CCACHE_SLOPPINESS=pch_defines,time_macros * Update CMakeLists.txt
halide · Mar 16, 2021 · 5aa1a65 · 5aa1a65
1 parent b061a32
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diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -42,6 +42,25 @@ set(CMAKE_CXX_STANDARD 14)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
+# Build Halide with ccache if the package is present
+option(Halide_CCACHE_BUILD "Set to ON for a ccache enabled build" OFF)
+if (Halide_CCACHE_BUILD)
+    find_program(CCACHE_PROGRAM ccache)
+    if (CCACHE_PROGRAM)
+        # TODO: ccache recommends setting CCACHE_SLOPPINESS=pch_defines,time_macros to
+        # enable precompiled header caching. Our timing found it slightly faster with
+        # just CCACHE_SLOPPINESS=pch_defines, so that's what we're using. Maybe revisit
+        # if issues occur (but we don't use any of the time macros so should be irrelevant).
+        set(Halide_CCACHE_PARAMS CCACHE_CPP2=yes CCACHE_HASHDIR=yes CCACHE_SLOPPINESS=pch_defines
+            CACHE STRING "Parameters to pass through to ccache")
+        set(CMAKE_C_COMPILER_LAUNCHER ${CMAKE_COMMAND} -E env ${Halide_CCACHE_PARAMS} ${CCACHE_PROGRAM})
+        set(CMAKE_CXX_COMPILER_LAUNCHER ${CMAKE_COMMAND} -E env ${Halide_CCACHE_PARAMS} ${CCACHE_PROGRAM})
+        message(STATUS "Enabling ccache usage for building.")
+    else ()
+        message(FATAL_ERROR "Unable to find the program ccache. Set Halide_CCACHE_BUILD to OFF")
+    endif ()
+endif ()
+
 ##
 # Import dependencies
 ##

diff --git a/README_cmake.md b/README_cmake.md
@@ -367,6 +367,7 @@ compiled.
 | `Halide_ENABLE_EXCEPTIONS`               | `ON`                  | Enable exceptions when building Halide                                                                           |
 | `Halide_USE_CODEMODEL_LARGE`             | `OFF`                 | Use the Large LLVM codemodel                                                                                     |
 | `Halide_TARGET`                          | _empty_               | The default target triple to use for `add_halide_library` (and the generator tests, by extension)                |
+| `Halide_CCACHE_BUILD`                    | `OFF`                 | Use ccache to accelerate rebuilds.                                                                               |
 
 The following options are only available when building Halide directly, ie. not
 through the [`add_subdirectory`][add_subdirectory] or