Add a config note and fix a config variable regarding CCACHE support.

[mattd]

Summary

• Mention in the CMake configuration documentation that LLVM builds, support the use of ccache.
• Use CCACHE_MAXSIZE instead of CCACHE_SIZE. The former is recognized by ccache, not the latter.
• Rename the LLVM CMake configuration variable to reflect that change: LLVM_CCACHE_SIZE -> LLVM_CCACHE_MAXSIZE

[probinson]

I know off-list I had suggested not bothering with detailed descriptions of LLVM_CCACHE_SIZE and LLVM_CCACHE_DIR, but now I am not so sure. If those variables map directly to ccache command-line arguments, we should say that here, and people can figure out how to set them by looking at the appropriate help. If the variables are more complicated, we should add separate entries for them in this doc.

[probinson]

See inline comment. I think that makes it clear enough where to look for details about what values to use for the MAXSIZE/DIR parameters.

docs/CMake.rst

559 ↗

(On Diff #128807)

... options, which are passed to the CCACHE_MAXSIZE and CCACHE_DIR environment variables, respectively.

[mattd]

Thanks Paul, I like that suggestion.

[probinson]

LGTM

[mattd]

Ping. Since I don't have commit access I'll need someone else to commit this on my behalf.

[sgundapa]

Thanks for taking care of this

[mattd]

No problem!

llvm/trunk/CMakeLists.txt

foreach(proj ${LLVM_ENABLE_PROJECTS})
   endif()
 endforeach()
 
 # 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_SIZE "" CACHE STRING "Size of ccache")
+      set(LLVM_CCACHE_MAXSIZE "" CACHE STRING "Size of ccache")
       set(LLVM_CCACHE_DIR "" CACHE STRING "Directory to keep ccached data")
       set(CCACHE_PROGRAM "CCACHE_CPP2=yes CCACHE_HASHDIR=yes ${CCACHE_PROGRAM}")
-      if (LLVM_CCACHE_SIZE)
-        set(CCACHE_PROGRAM "CCACHE_SIZE=${LLVM_CCACHE_SIZE} ${CCACHE_PROGRAM}")
+      if (LLVM_CCACHE_MAXSIZE)
+        set(CCACHE_PROGRAM "CCACHE_MAXSIZE=${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()
     message(FATAL_ERROR "Unable to find the program ccache. Set LLVM_CCACHE_BUILD to OFF")
   endif()

llvm/trunk/docs/CMake.rst

**LLVM_REVERSE_ITERATION**:BOOL
   reverse order. This is useful for uncovering non-determinism caused by
   iteration of unordered containers.
 
 **LLVM_BUILD_INSTRUMENTED_COVERAGE**:BOOL
   If enabled, `source-based code coverage
   <http://clang.llvm.org/docs/SourceBasedCodeCoverage.html>`_ instrumentation
   is enabled while building llvm.
 
+**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.
+
 CMake Caches
 ============
 
 Recently LLVM and Clang have been adding some more complicated build system
 features. Utilizing these new features often involves a complicated chain of
 CMake variables passed on the command line. Clang provides a collection of CMake
 cache scripts to make these features more approachable.