[LLD][COFF] Add LLVM toolchain library paths by default.

We want lld-link to automatically find compiler-rt's and
libc++ when it's in the same directory as the rest of the
toolchain. This is because on Windows linking isn't done
via the clang driver - but instead invoked directly.

This prepends: <llvm>/lib <llvm>/lib/clang/XX/lib and
<llvm>/lib/clang/XX/lib/windows automatically to the library
search paths.

Related to #63827

Differential Revision: https://reviews.llvm.org/D151188

Author: tru

clang/lib/Driver/Driver.cpp

@@ -184,6 +184,8 @@ std::string Driver::GetResourcesPath(StringRef BinaryPath,
     // path of the embedding binary, which for LLVM binaries will be in bin/.
     // ../lib gets us to lib/ in both cases.
     P = llvm::sys::path::parent_path(Dir);
+    // This search path is also created in the COFF driver of lld, so any
+    // changes here also needs to happen in lld/COFF/Driver.cpp
     llvm::sys::path::append(P, CLANG_INSTALL_LIBDIR_BASENAME, "clang",
                             CLANG_VERSION_MAJOR_STRING);
   }

lld/COFF/Driver.cpp

@@ -637,6 +637,31 @@ void LinkerDriver::detectWinSysRoot(const opt::InputArgList &Args) {
   }
 }
 
+void LinkerDriver::addClangLibSearchPaths(const std::string &argv0) {
+  std::string lldBinary = sys::fs::getMainExecutable(argv0.c_str(), nullptr);
+  SmallString<128> binDir(lldBinary);
+  sys::path::remove_filename(binDir); // remove lld-link.exe
+  StringRef rootDir = sys::path::parent_path(binDir); // remove 'bin'
+
+  SmallString<128> libDir(rootDir);
+  sys::path::append(libDir, "lib");
+  // We need to prepend the paths here in order to make sure that we always
+  // try to link the clang versions of the builtins over the ones supplied by MSVC.
+  searchPaths.insert(searchPaths.begin(), saver().save(libDir.str()));
+
+  // Add the resource dir library path
+  SmallString<128> runtimeLibDir(rootDir);
+  sys::path::append(runtimeLibDir, "lib", "clang", std::to_string(LLVM_VERSION_MAJOR), "lib");
+  searchPaths.insert(searchPaths.begin(), saver().save(runtimeLibDir.str()));
+
+  // Resource dir + osname, which is hardcoded to windows since we are in the
+  // COFF driver.
+  SmallString<128> runtimeLibDirWithOS(runtimeLibDir);
+  sys::path::append(runtimeLibDirWithOS, "windows");
+  searchPaths.insert(searchPaths.begin(), saver().save(runtimeLibDirWithOS.str()));
+
+}
+
 void LinkerDriver::addWinSysRootLibSearchPaths() {
   if (!diaPath.empty()) {
     // The DIA SDK always uses the legacy vc arch, even in new MSVC versions.
@@ -1543,6 +1568,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   detectWinSysRoot(args);
   if (!args.hasArg(OPT_lldignoreenv) && !args.hasArg(OPT_winsysroot))
     addLibSearchPaths();
+  addClangLibSearchPaths(argsArr[0]);
 
   // Handle /ignore
   for (auto *arg : args.filtered(OPT_ignore)) {

lld/COFF/Driver.h

@@ -84,6 +84,8 @@ class LinkerDriver {
   // config->machine has been set.
   void addWinSysRootLibSearchPaths();
 
+  void addClangLibSearchPaths(const std::string &argv0);
+
   // Used by the resolver to parse .drectve section contents.
   void parseDirectives(InputFile *file);
 

lld/docs/ReleaseNotes.rst

@@ -42,6 +42,12 @@ COFF Improvements
   current directory.
   I.e. ``lld-link /libpath:c:\relative\root relative\path\my.lib`` where before
   we would have to do ``lld-link /libpath:c:\relative\root\relative\path my.lib``
+* lld-link learned -print-search-paths that will print all the paths where it will
+  search for libraries.
+* By default lld-link will now search for libraries in the toolchain directories.
+  Specifically it will search:
+  ``<toolchain>/lib``, ``<toolchain>/lib/clang/<version>/lib`` and
+  ``<toolchain>/lib/clang/<version>/lib/windows``.
 
 MinGW Improvements
 ------------------

lld/test/COFF/print-search-paths.s

@@ -4,11 +4,17 @@
 # RUN: llvm-mc -triple i686-windows-msvc %s -filetype=obj -o %t_32.obj
 # RUN: lld-link -safeseh:no /dll /noentry /winsysroot:%t.dir/sysroot /vctoolsversion:1.1.1.1 /winsdkversion:10.0.1 %t_32.obj -print-search-paths | FileCheck -DSYSROOT=%t.dir -check-prefix=X86 %s
 # CHECK: Library search paths:
+# CHECK:   [[CPATH:.*]]lib{{[/\\]}}clang{{[/\\]}}{{[0-9]+}}{{[/\\]}}lib{{[/\\]}}windows
+# CHECK:   [[CPATH]]lib{{[/\\]}}clang{{[/\\]}}{{[0-9]+}}{{[/\\]}}lib
+# CHECK:   [[CPATH]]lib
 # CHECK:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}VC{{[/\\]}}Tools{{[/\\]}}MSVC{{[/\\]}}1.1.1.1{{[/\\]}}lib{{[/\\]}}x64
 # CHECK:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}VC{{[/\\]}}Tools{{[/\\]}}MSVC{{[/\\]}}1.1.1.1{{[/\\]}}atlmfc{{[/\\]}}lib{{[/\\]}}x64
 # CHECK:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}Windows Kits{{[/\\]}}10{{[/\\]}}Lib{{[/\\]}}10.0.1{{[/\\]}}ucrt{{[/\\]}}x64
 # CHECK:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}Windows Kits{{[/\\]}}10{{[/\\]}}Lib{{[/\\]}}10.0.1{{[/\\]}}um{{[/\\]}}x64
 # X86: Library search paths:
+# X86:   [[CPATH:.*]]lib{{[/\\]}}clang{{[/\\]}}{{[0-9]+}}{{[/\\]}}lib{{[/\\]}}windows
+# X86:   [[CPATH]]lib{{[/\\]}}clang{{[/\\]}}{{[0-9]+}}{{[/\\]}}lib
+# X86:   [[CPATH]]lib
 # X86:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}VC{{[/\\]}}Tools{{[/\\]}}MSVC{{[/\\]}}1.1.1.1{{[/\\]}}lib{{[/\\]}}x86
 # X86:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}VC{{[/\\]}}Tools{{[/\\]}}MSVC{{[/\\]}}1.1.1.1{{[/\\]}}atlmfc{{[/\\]}}lib{{[/\\]}}x86
 # X86:   [[SYSROOT]]{{[/\\]}}sysroot{{[/\\]}}Windows Kits{{[/\\]}}10{{[/\\]}}Lib{{[/\\]}}10.0.1{{[/\\]}}ucrt{{[/\\]}}x86