diff --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
--- a/clang/docs/ClangCommandLineReference.rst
+++ b/clang/docs/ClangCommandLineReference.rst
@@ -18,9 +18,9 @@
 
 
 .. program:: clang
-.. option:: -B<dir>, --prefix <arg>, --prefix=<arg>
+.. option:: -B<prefix>, --prefix <arg>, --prefix=<arg>
 
-Add <dir> to search path for binaries and object files used implicitly
+Search $prefix/$triple-$file and $prefix$file for executables, libraries, includes, and data files used by the compiler. $prefix may or may not be a directory
 
 .. option:: -F<arg>
 
@@ -256,7 +256,7 @@
 
 .. option:: --gcc-toolchain=<arg>, -gcc-toolchain <arg>
 
-Use the gcc toolchain at the given directory
+Search for GCC installation in the specified directory on targets which commonly use GCC. The directory usually contains 'lib{,32,64}/gcc{,-cross}/$triple' and 'include'. If specified, sysroot is skipped for GCC detection. Note: executables (e.g. ld) used by the compiler are not overridden by the selected GCC installation
 
 .. option:: -gcodeview
 
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -601,8 +601,14 @@
 def _DASH_DASH : Option<["--"], "", KIND_REMAINING_ARGS>,
     Flags<[NoXarchOption, CoreOption]>;
 def A : JoinedOrSeparate<["-"], "A">, Flags<[RenderJoined]>, Group<gfortran_Group>;
-def B : JoinedOrSeparate<["-"], "B">, MetaVarName<"<dir>">,
-    HelpText<"Add <dir> to search path for binaries and object files used implicitly">;
+def B : JoinedOrSeparate<["-"], "B">, MetaVarName<"<prefix>">,
+    HelpText<"Search $prefix/$triple-$file and $prefix$file for executables, libraries, "
+    "includes, and data files used by the compiler. $prefix may or may not be a directory">;
+def gcc_toolchain : Joined<["--"], "gcc-toolchain=">, Flags<[NoXarchOption]>,
+  HelpText<"Search for GCC installation in the specified directory on targets which commonly use GCC. "
+  "The directory usually contains 'lib{,32,64}/gcc{,-cross}/$triple' and 'include'. If specified, "
+  "sysroot is skipped for GCC detection. Note: executables (e.g. ld) used by the compiler are not "
+  "overridden by the selected GCC installation">;
 def CC : Flag<["-"], "CC">, Flags<[CC1Option]>, Group<Preprocessor_Group>,
     HelpText<"Include comments from within macros in preprocessed output">,
     MarshallingInfoFlag<PreprocessorOutputOpts<"ShowMacroComments">>;
@@ -3671,8 +3677,6 @@
   MarshallingInfoFlag<FrontendOpts<"PrintSupportedCPUs">>;
 def mcpu_EQ_QUESTION : Flag<["-"], "mcpu=?">, Alias<print_supported_cpus>;
 def mtune_EQ_QUESTION : Flag<["-"], "mtune=?">, Alias<print_supported_cpus>;
-def gcc_toolchain : Joined<["--"], "gcc-toolchain=">, Flags<[NoXarchOption]>,
-  HelpText<"Use the gcc toolchain at the given directory">;
 def time : Flag<["-"], "time">,
   HelpText<"Time individual commands">;
 def traditional_cpp : Flag<["-", "--"], "traditional-cpp">, Flags<[CC1Option]>,