Support setting default value for -rtlib at build time

This patch introduces a new cmake variable: CLANG_DEFAULT_RTLIB, thru
which we can specify a default value for -rtlib (libgcc or
compiler-rt) at build time, just like how we set the default C++
stdlib thru CLANG_DEFAULT_CXX_STDLIB.

With these two options, we can configure clang to build binaries on
Linux that have no runtime dependence on any gcc libs (libstdc++ or
libgcc_s).

Patch by Lei Zhang!

Differential Revision: https://reviews.llvm.org/D22663

llvm-svn: 276848

1 files changed, 14 insertions, 9 deletions

diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index f05261aef30..610285e1f40 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -403,18 +403,23 @@ void DarwinClang::AddLinkSanitizerLibArgs(const ArgList &Args,
       /*AddRPath*/ true);
 }
 
+ToolChain::RuntimeLibType DarwinClang::GetRuntimeLibType(
+    const ArgList &Args) const {
+  if (Arg* A = Args.getLastArg(options::OPT_rtlib_EQ)) {
+    StringRef Value = A->getValue();
+    if (Value != "compiler-rt")
+      getDriver().Diag(diag::err_drv_unsupported_rtlib_for_platform)
+          << Value << "darwin";
+  }
+
+  return ToolChain::RLT_CompilerRT;
+}
+
 void DarwinClang::AddLinkRuntimeLibArgs(const llvm::Triple &EffectiveTriple,
                                         const ArgList &Args,
                                         ArgStringList &CmdArgs) const {
-  // Darwin only supports the compiler-rt based runtime libraries.
-  switch (GetRuntimeLibType(Args)) {
-  case ToolChain::RLT_CompilerRT:
-    break;
-  default:
-    getDriver().Diag(diag::err_drv_unsupported_rtlib_for_platform)
-        << Args.getLastArg(options::OPT_rtlib_EQ)->getValue() << "darwin";
-    return;
-  }
+  // Call once to ensure diagnostic is printed if wrong value was specified
+  GetRuntimeLibType(Args);
 
   // Darwin doesn't support real static executables, don't link any runtime
   // libraries with -static.