[clang][Driver] Add a new member for CLANG_DEFAULT_LINKER to clang::driver::Driver (NFC)

The default linker can be changed by a CMake variable CLANG_DEFAULT_LINKER,
but it is shared in all toolchains. This patch intends to resolve this.

Author: parabola94

clang/include/clang/Driver/Driver.h

@@ -337,6 +337,10 @@ class Driver {
   /// "clang" as it's first argument.
   const char *PrependArg;
 
+  /// The default value of -fuse-ld= option. An empty string means the default
+  /// system linker.
+  std::string PreferredLinker;
+
   /// Whether to check that input files exist when constructing compilation
   /// jobs.
   LLVM_PREFERRED_TYPE(bool)
@@ -450,6 +454,11 @@ class Driver {
     return ClangExecutable.c_str();
   }
 
+  StringRef getPreferredLinker() const { return PreferredLinker; }
+  void setPreferredLinker(std::string Value) {
+    PreferredLinker = std::move(Value);
+  }
+
   bool isSaveTempsEnabled() const { return SaveTemps != SaveTempsNone; }
   bool isSaveTempsObj() const { return SaveTemps == SaveTempsObj; }
 

clang/lib/Driver/Driver.cpp

@@ -266,8 +266,8 @@ Driver::Driver(StringRef ClangExecutable, StringRef TargetTriple,
       CCLogDiagnostics(false), CCGenDiagnostics(false),
       CCPrintProcessStats(false), CCPrintInternalStats(false),
       TargetTriple(TargetTriple), Saver(Alloc), PrependArg(nullptr),
-      CheckInputsExist(true), ProbePrecompiled(true),
-      SuppressMissingInputWarning(false) {
+      PreferredLinker(CLANG_DEFAULT_LINKER), CheckInputsExist(true),
+      ProbePrecompiled(true), SuppressMissingInputWarning(false) {
   // Provide a sane fallback if no VFS is specified.
   if (!this->VFS)
     this->VFS = llvm::vfs::getRealFileSystem();

clang/lib/Driver/ToolChain.cpp

@@ -1100,7 +1100,7 @@ std::string ToolChain::GetLinkerPath(bool *LinkerIsLLD) const {
   // Get -fuse-ld= first to prevent -Wunused-command-line-argument. -fuse-ld= is
   // considered as the linker flavor, e.g. "bfd", "gold", or "lld".
   const Arg* A = Args.getLastArg(options::OPT_fuse_ld_EQ);
-  StringRef UseLinker = A ? A->getValue() : CLANG_DEFAULT_LINKER;
+  StringRef UseLinker = A ? A->getValue() : getDriver().getPreferredLinker();
 
   // --ld-path= takes precedence over -fuse-ld= and specifies the executable
   // name. -B, COMPILER_PATH and PATH and consulted if the value does not

clang/lib/Driver/ToolChains/MSVC.cpp

@@ -279,8 +279,8 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
     AddRunTimeLibs(TC, TC.getDriver(), CmdArgs, Args);
   }
 
-  StringRef Linker =
-      Args.getLastArgValue(options::OPT_fuse_ld_EQ, CLANG_DEFAULT_LINKER);
+  StringRef Linker = Args.getLastArgValue(options::OPT_fuse_ld_EQ,
+                                          TC.getDriver().getPreferredLinker());
   if (Linker.empty())
     Linker = "link";
   // We need to translate 'lld' into 'lld-link'.

clang/lib/Driver/ToolChains/MinGW.cpp

@@ -548,7 +548,7 @@ toolchains::MinGW::MinGW(const Driver &D, const llvm::Triple &Triple,
     getFilePaths().push_back(Base + "lib");
 
   NativeLLVMSupport =
-      Args.getLastArgValue(options::OPT_fuse_ld_EQ, CLANG_DEFAULT_LINKER)
+      Args.getLastArgValue(options::OPT_fuse_ld_EQ, D.getPreferredLinker())
           .equals_insensitive("lld");
 }
 

clang/lib/Driver/ToolChains/Solaris.cpp

@@ -39,7 +39,7 @@ void solaris::Assembler::ConstructJob(Compilation &C, const JobAction &JA,
 bool solaris::isLinkerGnuLd(const ToolChain &TC, const ArgList &Args) {
   // Only used if targetting Solaris.
   const Arg *A = Args.getLastArg(options::OPT_fuse_ld_EQ);
-  StringRef UseLinker = A ? A->getValue() : CLANG_DEFAULT_LINKER;
+  StringRef UseLinker = A ? A->getValue() : TC.getDriver().getPreferredLinker();
   return UseLinker == "bfd" || UseLinker == "gld";
 }
 
@@ -52,7 +52,7 @@ static bool getPIE(const ArgList &Args, const ToolChain &TC) {
                       TC.isPIEDefault(Args));
 }
 
-// FIXME: Need to handle CLANG_DEFAULT_LINKER here?
+// FIXME: Need to handle PreferredLinker here?
 std::string solaris::Linker::getLinkerPath(const ArgList &Args) const {
   const ToolChain &ToolChain = getToolChain();
   if (const Arg *A = Args.getLastArg(options::OPT_fuse_ld_EQ)) {
@@ -345,7 +345,7 @@ SanitizerMask Solaris::getSupportedSanitizers() const {
 
 const char *Solaris::getDefaultLinker() const {
   // FIXME: Only handle Solaris ld and GNU ld here.
-  return llvm::StringSwitch<const char *>(CLANG_DEFAULT_LINKER)
+  return llvm::StringSwitch<const char *>(getDriver().getPreferredLinker())
       .Cases("bfd", "gld", "/usr/gnu/bin/ld")
       .Default("/usr/bin/ld");
 }

clang/lib/Driver/ToolChains/UEFI.cpp

@@ -83,8 +83,8 @@ void tools::uefi::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   // This should ideally be handled by ToolChain::GetLinkerPath but we need
   // to special case some linker paths. In the case of lld, we need to
   // translate 'lld' into 'lld-link'.
-  StringRef Linker =
-      Args.getLastArgValue(options::OPT_fuse_ld_EQ, CLANG_DEFAULT_LINKER);
+  StringRef Linker = Args.getLastArgValue(options::OPT_fuse_ld_EQ,
+                                          TC.getDriver().getPreferredLinker());
   if (Linker.empty() || Linker == "lld")
     Linker = "lld-link";