Add clang flag equivalent to clang-cl /Zl flag

[akhuang]

Summary

The /Zl flag omits default C runtime library name from obj files.
This patch just adds an equivalent clang driver flag.

[mstorsjo]

clang/include/clang/Driver/Options.td

2230

Initially, I'm not entirely sure about the option name - initially it feels weird/clumsy, but after thinking about it, I'm not sure if I can come up with something better either. Maybe just -fms-omit-default-lib?

[hans]

Could the new flag be marked as an Alias in the tablegen, so that we don't need to do any code changes for it?

[akhuang]

In D133959#3793283, @hans wrote:

Could the new flag be marked as an Alias in the tablegen, so that we don't need to do any code changes for it?

It appears before _SLASH_Zl in the file so we'd have to move it out of place. We could alias /Zl to the new flag.

[akhuang]

Change name of flag, and alias /Zl to this flag.

[hans]

lgtm

clang/include/clang/Driver/Options.td

2231

Might as well add a help text while we're here?

[mstorsjo]

clang/test/Driver/cl-runtime-flags.c

101

This testcase doesn't seem to be updated with the new name of the option?

[akhuang]

Fix flag name in test case

[mstorsjo]

LGTM, thanks!

clang/include/clang/Driver/Options.td

 def fms_runtime_lib_EQ : Joined<["-"], "fms-runtime-lib=">, Group<f_Group>,
   Flags<[NoXarchOption, CoreOption]>, Values<"static,static_dbg,dll,dll_dbg">,
   HelpText<"Select Windows run-time library">,
   DocBrief<[{
 Specify Visual Studio C runtime library. "static" and "static_dbg" correspond
 to the cl flags /MT and /MTd which use the multithread, static version. "dll"
 and "dll_dbg" correspond to the cl flags /MD and /MDd which use the multithread,
 dll version.}]>;
+def fms_omit_default_lib : Joined<["-"], "fms-omit-default-lib">,
+  Group<f_Group>, Flags<[NoXarchOption, CoreOption]>;
 defm delayed_template_parsing : BoolFOption<"delayed-template-parsing",
   LangOpts<"DelayedTemplateParsing">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Parse templated function definitions at the end of the translation unit">,
   NegFlag<SetFalse, [NoXarchOption], "Disable delayed template parsing">,
   BothFlags<[CoreOption]>>;
 def fms_memptr_rep_EQ : Joined<["-"], "fms-memptr-rep=">, Group<f_Group>, Flags<[CC1Option]>,
   Values<"single,multiple,virtual">, NormalizedValuesScope<"LangOptions">,
   NormalizedValues<["PPTMK_FullGeneralitySingleInheritance", "PPTMK_FullGeneralityMultipleInheritance",

 def _SLASH_vmv : CLFlag<"vmv">,
   HelpText<"Set the default most-general representation to "
            "virtual inheritance">;
 def _SLASH_volatile_ms  : Option<["/", "-"], "volatile:ms", KIND_FLAG>,
   Group<_SLASH_volatile_Group>, Flags<[CLOption, NoXarchOption]>,
   HelpText<"Volatile loads and stores have acquire and release semantics">;
 def _SLASH_clang : CLJoined<"clang:">,
   HelpText<"Pass <arg> to the clang driver">, MetaVarName<"<arg>">;
-def _SLASH_Zl : CLFlag<"Zl">,
+def _SLASH_Zl : CLFlag<"Zl">, Alias<fms_omit_default_lib>,
   HelpText<"Do not let object file auto-link default libraries">;
 
 def _SLASH_Yc : CLJoined<"Yc">,
   HelpText<"Generate a pch file for all code up to and including <filename>">,
   MetaVarName<"<filename>">;
 def _SLASH_Yu : CLJoined<"Yu">,
   HelpText<"Load a pch file and use it instead of all code up to "
            "and including <filename>">,

clang/lib/Driver/ToolChains/Clang.cpp

case options::OPT__SLASH_MTd:
     CmdArgs.push_back("-D_MT");
     CmdArgs.push_back("-flto-visibility-public-std");
     FlagForCRT = "--dependent-lib=libcmtd";
     break;
   default:
     llvm_unreachable("Unexpected option ID.");
   }
 
-  if (Args.hasArg(options::OPT__SLASH_Zl)) {
+  if (Args.hasArg(options::OPT_fms_omit_default_lib)) {
     CmdArgs.push_back("-D_VC_NODEFAULTLIB");
   } else {
     CmdArgs.push_back(FlagForCRT.data());
 
     // This provides POSIX compatibility (maps 'open' to '_open'), which most
     // users want.  The /Za flag to cl.exe turns this off, but it's not
     // implemented in clang.
     CmdArgs.push_back("--dependent-lib=oldnames");

clang/test/Driver/cl-runtime-flags.c

 // CHECK-LDMDd: "-D_DLL"
 // CHECK-LDMDd: "--dependent-lib=msvcrtd"
 
 // RUN: %clang_cl /MD /MT -### -- %s 2>&1 | FileCheck -check-prefix=MTOVERRIDE %s
 // MTOVERRIDE: "--dependent-lib=libcmt"
 
 // RUN: %clang_cl -### /Zl -- %s 2>&1 | FileCheck -check-prefix=CHECK-MTZl %s
 // RUN: %clang_cl -### /MT /Zl -- %s 2>&1 | FileCheck -check-prefix=CHECK-MTZl %s
+// RUN: %clang -### --target=x86_64-windows-msvc -fms-runtime-lib=static \
+// RUN:   -fms-omit-default-lib -- %s 2>&1 | FileCheck \
+// RUN:   -check-prefix=CHECK-MTZl %s
 // CHECK-MTZl-NOT: "-D_DEBUG"
 // CHECK-MTZl: "-D_MT"
 // CHECK-MTZl-NOT: "-D_DLL"
 // CHECK-MTZl-SAME: "-D_VC_NODEFAULTLIB"
 // CHECK-MTZl-NOT: "--dependent-lib=libcmt"
 // CHECK-MTZl-NOT: "--dependent-lib=oldnames"