Document option '-rtlib' in clang's man page and help info

[zlei]

Summary

This patch adds an entry for "-rtlib" in the output of man clang and clang -help.

[bruno]

Hi Lei,

Thanks for the doc improvement!

docs/CommandGuide/clang.rst

114

It might be worth mentioning what's the default behaviour in case the flag isn't specified?

[zlei]

docs/CommandGuide/clang.rst

114

This option behaves a lot like -stdlib, so I want their doc entries to look alike too. Perhaps I should update them both to state the default behavior?

[bruno]

docs/CommandGuide/clang.rst

114

That would be great, but feel free to do this update in follow up patches/commits if you want to.

[zlei]

Update the man page entry to state default behavior of this option.

[Hahnfeld]

LGTM, thanks for the improvement!

[Hahnfeld]

@zlei will you commit the patch or do you want me to do that on your behalf?

[zlei]

In D24069#540804, @Hahnfeld wrote:

@zlei will you commit the patch or do you want me to do that on your behalf?

I don't have commit access, so please do me a favor :)

docs/CommandGuide/clang.rst

 
  Specify the language standard to compile for.
 
 .. option:: -stdlib=<library>
 
  Specify the C++ standard library to use; supported options are libstdc++ and
  libc++.
 
+.. option:: -rtlib=<library>
+
+ Specify the compiler runtime library to use; supported options are libgcc and
+ compiler-rt.
+
 .. option:: -ansi
 
  Same as -std=c89.
 
 .. option:: -ObjC, -ObjC++
 
  Treat source input files as Objective-C and Object-C++ inputs respectively.
 

include/clang/Driver/Options.td

def rewrite_legacy_objc : Flag<["-"], "rewrite-legacy-objc">, Flags<[DriverOption]>,
   HelpText<"Rewrite Legacy Objective-C source to C++">;
 def rdynamic : Flag<["-"], "rdynamic">;
 def resource_dir : Separate<["-"], "resource-dir">,
   Flags<[DriverOption, CC1Option, CoreOption, HelpHidden]>,
   HelpText<"The directory which holds the compiler resource files">;
 def resource_dir_EQ : Joined<["-"], "resource-dir=">, Flags<[DriverOption]>,
   Alias<resource_dir>;
 def rpath : Separate<["-"], "rpath">, Flags<[LinkerInput]>;
-def rtlib_EQ : Joined<["-", "--"], "rtlib=">;
+def rtlib_EQ : Joined<["-", "--"], "rtlib=">,
+  HelpText<"Compiler runtime library to use">;
 def r : Flag<["-"], "r">, Flags<[LinkerInput,NoArgumentUnused]>;
 def save_temps_EQ : Joined<["-", "--"], "save-temps=">, Flags<[DriverOption]>,
   HelpText<"Save intermediate compilation results.">;
 def save_temps : Flag<["-", "--"], "save-temps">, Flags<[DriverOption]>,
   Alias<save_temps_EQ>, AliasArgs<["cwd"]>,
   HelpText<"Save intermediate compilation results">;
 def via_file_asm : Flag<["-", "--"], "via-file-asm">, InternalDebugOpt,
   HelpText<"Write assembly to file for input to assemble jobs">;