[CMake] Updating caches README with explanations of useful cache files.

This is in response to silvas' post-commit suggestion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@260203 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 64 insertions, 8 deletions

diff --git a/cmake/caches/README.txt b/cmake/caches/README.txt
index 55e5e159db..db5c85a68f 100644
--- a/cmake/caches/README.txt
+++ b/cmake/caches/README.txt
@@ -4,15 +4,71 @@ CMake Caches
 This directory contains CMake cache scripts that pre-populate the CMakeCache in
 a build directory with commonly used settings.
 
-The first two cache files in the directory are used by Apple to build the clang
-distribution packaged with Xcode. You can use the caches with the following
-CMake invocation:
+You can use the caches files with the following CMake invocation:
 
 cmake -G <build system>
-  -C <path to llvm>/tools/clang/cmake/caches/Apple-stage1.cmake
-  -DCMAKE_BUILD_TYPE=Release
-  [-DCMAKE_INSTALL_PREFIX=<install path>]
+  -C <path to cache file>
+  [additional CMake options (i.e. -DCMAKE_INSTALL_PREFIX=<install path>)]
   <path to llvm>
 
-Building the `bootstrap` target from this generation will build clang, and
-`bootstrap-install` will install it.
+Options specified on the command line will override options in the cache files.
+
+The following cache files exist.
+
+Apple-stage1
+------------
+
+The Apple stage1 cache configures a two stage build similar to how Apple builds
+the clang shipped with Xcode. The build files generated from this invocation has
+a target named "stage2" which performs an LTO build of clang.
+
+The Apple-stage2 cache can be used directly to match the build settings Apple
+uses in shipping builds without doing a full bootstrap build.
+
+PGO
+---
+
+The PGO CMake cache can be used to generate a multi-stage instrumented compiler.
+You can configure your build directory with the following invocation of CMake:
+
+cmake -G <generator> -C <path_to_clang>/cmake/caches/PGO.cmake <source dir>
+
+After configuration the following additional targets will be generated:
+
+stage2-instrumented:
+Builds a stage1 x86 compiler, runtime, and required tools (llvm-config,
+llvm-profdata) then uses that compiler to build an instrumented stage2 compiler.
+
+stage2-instrumented-generate-profdata:
+Depends on "stage2-instrumented" and will use the instrumented compiler to
+generate profdata based on the training files in <clang>/utils/perf-training
+
+stage2:
+Depends on "stage2-instrumented-generate-profdata" and will use the stage1
+compiler with the stage2 profdata to build a PGO-optimized compiler.
+
+stage2-check-llvm:
+Depends on stage2 and runs check-llvm using the stage3 compiler.
+
+stage2-check-clang:
+Depends on stage2 and runs check-clang using the stage3 compiler.
+
+stage2-check-all:
+Depends on stage2 and runs check-all using the stage3 compiler.
+
+stage2-test-suite:
+Depends on stage2 and runs the test-suite using the stage3 compiler (requires
+in-tree test-suite).
+
+3-stage
+-------
+
+This cache file can be used to generate a 3-stage clang build. You can configure
+using the following CMake command:
+
+cmake -C <path to clang>/cmake/caches/3-stage.cmake -G Ninja <path to llvm>
+
+You can then run "ninja stage3-clang" to build stage1, stage2 and stage3 clangs.
+
+This is useful for finding non-determinism the compiler by verifying that stage2
+and stage3 are identical.