Index: clang-check/ClangCheck.cpp
===================================================================
--- clang-check/ClangCheck.cpp
+++ clang-check/ClangCheck.cpp
@@ -10,27 +10,6 @@
 //  This file implements a clang-check tool that runs the
 //  clang::SyntaxOnlyAction over a number of translation units.
 //
-//  Usage:
-//  clang-check <cmake-output-dir> <file1> <file2> ...
-//
-//  Where <cmake-output-dir> is a CMake build directory in which a file named
-//  compile_commands.json exists (enable -DCMAKE_EXPORT_COMPILE_COMMANDS in
-//  CMake to get this output).
-//
-//  <file1> ... specify the paths of files in the CMake source tree. This  path
-//  is looked up in the compile command database. If the path of a file is
-//  absolute, it needs to point into CMake's source tree. If the path is
-//  relative, the current working directory needs to be in the CMake source
-//  tree and the file must be in a subdirectory of the current working
-//  directory. "./" prefixes in the relative files will be automatically
-//  removed, but the rest of a relative path must be a suffix of a path in
-//  the compile command line database.
-//
-//  For example, to use clang-check on all files in a subtree of the source
-//  tree, use:
-//
-//    /path/in/subtree $ find . -name '*.cpp'| xargs clang-check /path/to/source
-//
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/CommandLine.h"
@@ -43,7 +22,7 @@
 
 cl::opt<std::string> BuildPath(
   "p",
-  cl::desc("<build-path>"),
+  cl::desc("<cmake-output-dir>"),
   cl::Optional);
 
 cl::list<std::string> SourcePaths(
@@ -51,6 +30,34 @@
   cl::desc("<source0> [... <sourceN>]"),
   cl::OneOrMore);
 
+static cl::extrahelp MoreHelp(
+    "\n"
+    "<cmake-output-dir> is a CMake build directory in which a file named\n"
+    "compile_commands.json exists (enable -DCMAKE_EXPORT_COMPILE_COMMANDS in\n"
+    "CMake to get this output). When a CMake output directory is not\n"
+    "specified, clang-check will attempt to locate compile_commands.json\n"
+    "automatically in all parent paths of the first input file.\n"
+    "\n"
+    "<source0> ... specify the paths of files in the CMake source tree. This\n"
+    "path is looked up in the compile command database. If the path of a file\n"
+    "is absolute, it needs to point into CMake's source tree. If the path is\n"
+    "relative, the current working directory needs to be in the CMake source\n"
+    "tree and the file must be in a subdirectory of the current working\n"
+    "directory. \"./\" prefixes in the relative files will be automatically\n"
+    "removed, but the rest of a relative path must be a suffix of a path in\n"
+    "the compile command line database.\n"
+    "\n"
+    "For example, to use clang-check on all files in a subtree of the source\n"
+    "tree, use:\n"
+    "\n"
+    "  find path/in/subtree -name '*.cpp'|xargs clang-check -p path/to/source\n"
+    "\n"
+    "or using auto-location of compile_commands.json:\n"
+    "\n"
+    "  find path/in/subtree -name '*.cpp'|xargs clang-check\n"
+    "\n"
+);
+
 int main(int argc, const char **argv) {
   llvm::OwningPtr<CompilationDatabase> Compilations(
     FixedCompilationDatabase::loadFromCommandLine(argc, argv));