[Darwin] Stop linking libclang_rt.eprintf.a

[beanz]

Summary

The eprintf library was added before the general OS X builtins library existed as a place to store one builtin function. Since we have for several years had an actual mandated builtin library for OS X > 10.5, we should just merge eprintf into the main library.

This change will resolve PR28855.

As a follow up I'll also patch compiler-rt to not generate the eprintf library anymore.

[echristo]

LGTM.

Might want to fix the braces while you're there.

-eric

[beanz]

Updating code comment and removing unneeded braces.

I'm going to sit on this for a bit before committing in case anyone comes up with a reason this is a bad idea.

cfe/trunk/lib/Driver/ToolChains.cpp

if (isTargetWatchOSBased()) {
     assert(isTargetMacOS() && "unexpected non MacOS platform");
     // The dynamic runtime library was merged with libSystem for 10.6 and
     // beyond; only 10.4 and 10.5 need an additional runtime library.
     if (isMacosxVersionLT(10, 5))
       CmdArgs.push_back("-lgcc_s.10.4");
     else if (isMacosxVersionLT(10, 6))
       CmdArgs.push_back("-lgcc_s.10.5");
 
-    // For OS X, we thought we would only need a static runtime library when
-    // targeting 10.4, to provide versions of the static functions which were
-    // omitted from 10.4.dylib.
+    // Originally for OS X, we thought we would only need a static runtime
+    // library when targeting 10.4, to provide versions of the static functions
+    // which were omitted from 10.4.dylib. This led to the creation of the 10.4
+    // builtins library.
     //
     // Unfortunately, that turned out to not be true, because Darwin system
     // headers can still use eprintf on i386, and it is not exported from
     // libSystem. Therefore, we still must provide a runtime library just for
     // the tiny tiny handful of projects that *might* use that symbol.
-    if (isMacosxVersionLT(10, 5)) {
+    //
+    // Then over time, we figured out it was useful to add more things to the
+    // runtime so we created libclang_rt.osx.a to provide new functions when
+    // deploying to old OS builds, and for a long time we had both eprintf and
+    // osx builtin libraries. Which just seems excessive. So with PR 28855, we
+    // are removing the eprintf library and expecting eprintf to be provided by
+    // the OS X builtins library.
+    if (isMacosxVersionLT(10, 5))
       AddLinkRuntimeLib(Args, CmdArgs, "libclang_rt.10.4.a");
-    } else {
-      if (getTriple().getArch() == llvm::Triple::x86)
-        AddLinkRuntimeLib(Args, CmdArgs, "libclang_rt.eprintf.a");
+    else
       AddLinkRuntimeLib(Args, CmdArgs, "libclang_rt.osx.a");
-    }
-  }
-}
 
 void Darwin::AddDeploymentTarget(DerivedArgList &Args) const {
   const OptTable &Opts = getDriver().getOpts();
 
   // Support allowing the SDKROOT environment variable used by xcrun and other
   // Xcode tools to define the default sysroot, by making it the default for
   // isysroot.
   if (const Arg *A = Args.getLastArg(options::OPT_isysroot)) {