[BUILD] Re-enable ccache by default

CMakeLists.txt

@@ -72,6 +72,7 @@ tvm_option(USE_PAPI "Use Performance Application Programming Interface (PAPI) to
 tvm_option(USE_GTEST "Use GoogleTest for C++ sanity tests" AUTO)
 tvm_option(USE_CUSTOM_LOGGING "Use user-defined custom logging, tvm::runtime::detail::LogFatalImpl and tvm::runtime::detail::LogMessageImpl must be implemented" OFF)
 tvm_option(USE_ALTERNATIVE_LINKER "Use 'mold' or 'lld' if found when invoking compiler to link artifact" AUTO)
+tvm_option(USE_CCACHE "Use ccache if found when invoking compiler" AUTO)
 
 # 3rdparty libraries
 tvm_option(DLPACK_PATH "Path to DLPACK" "3rdparty/dlpack/include")
@@ -460,6 +461,42 @@ if(USE_PIPELINE_EXECUTOR)
   list(APPEND RUNTIME_SRCS ${RUNTIME_PIPELINE_SRCS})
 endif(USE_PIPELINE_EXECUTOR)
 
+#Caches the build.
+#Note that ccache-3.x doesn't support nvcc well, so CUDA kernels may never hit the cache and still
+#need to be re-compiled every time. Using ccache 4.0+ can resolve this issue.
+
+if(USE_CCACHE) # True for AUTO, ON, /path/to/ccache
+  if(DEFINED CXX_COMPILER_LAUNCHER OR DEFINED C_COMPILER_LAUNCHER)
+    message(STATUS "CXX_COMPILER_LAUNCHER or C_COMPILER_LAUNCHER already defined, not using ccache")
+  else()
+    if("${USE_CCACHE}" STREQUAL "AUTO") # Auto mode
+      find_program(CCACHE_FOUND ccache)
+      if(CCACHE_FOUND)
+        message(STATUS "Found the path to ccache, enabling ccache")
+        set(PATH_TO_CCACHE ccache)
+      else()
+        message(STATUS "Didn't find the path to CCACHE, disabling ccache")
+      endif(CCACHE_FOUND)
+    elseif("${USE_CCACHE}" MATCHES ${IS_TRUE_PATTERN})
+      find_program(CCACHE_FOUND ccache)
+      if(CCACHE_FOUND)
+        message(STATUS "Found the path to ccache, enabling ccache")
+        set(PATH_TO_CCACHE ccache)
+      else()
+        message(FATAL_ERROR "Cannot find ccache. Set USE_CCACHE mode to AUTO or OFF to build without ccache. USE_CCACHE=" "${USE_CCACHE}")
+      endif(CCACHE_FOUND)
+    else() # /path/to/ccache
+      set(PATH_TO_CCACHE USE_CCACHE)
+      message(STATUS "Setting ccache path to " "${PATH_TO_CCACHE}")
+    endif()
+    # Set the flag for ccache
+    if(DEFINED PATH_TO_CCACHE)
+      set(CXX_COMPILER_LAUNCHER "${PATH_TO_CCACHE}")
+      set(C_COMPILER_LAUNCHER "${PATH_TO_CCACHE}")
+    endif()
+  endif()
+endif(USE_CCACHE)
+
 # Module rules
 include(cmake/modules/VTA.cmake)
 include(cmake/modules/StandaloneCrt.cmake)

cmake/config.cmake

@@ -352,6 +352,17 @@ set(USE_LIBBACKTRACE AUTO)
 # runtime functions to be unavailable to the program.
 set(BUILD_STATIC_RUNTIME OFF)
 
+# Caches the build so that building is faster when switching between branches.
+# If you switch branches, build and then encounter a linking error, you may
+# need to regenerate the build tree through "make .." (the cache will
+# still provide significant speedups).
+# Possible values:
+# - AUTO: search for path to ccache, disable if not found.
+# - ON: enable ccache by searching for the path to ccache, report an error if not found
+# - OFF: disable ccache
+# - /path/to/ccache: use specific path to ccache
+set(USE_CCACHE AUTO)
+
 # Whether to enable PAPI support in profiling. PAPI provides access to hardware
 # counters while profiling.
 # Possible values:

docs/install/from_source.rst

@@ -141,6 +141,8 @@ The configuration of TVM can be modified by editing `config.cmake` and/or by pas
   - On supported platforms, the `Ccache compiler wrapper <https://ccache.dev/>`_ may be helpful for
     reducing TVM's build time.  There are several ways to enable CCache in TVM builds:
 
+    - Leave `USE_CCACHE=AUTO` in `build/config.cmake`. CCache will be used if it is found.
+
     - Ccache's Masquerade mode. This is typically enabled during the Ccache installation process.
       To have TVM use Ccache in masquerade, simply specify the appropriate C/C++ compiler
       paths when configuring TVM's build system.  For example: