Integrate LLD 5.0+ for ELF and Mach-O targets

Requires LLD 5.0+, otherwise LDC aborts due to conflicting command-line
options.

Author: kinke

CMakeLists.txt

@@ -572,14 +572,25 @@ add_custom_target(${LDMD_EXE} ALL DEPENDS ${LDMD_EXE_FULL})
 
 # Figure out how to link the main LDC executable, for which we need to take the
 # LLVM flags into account.
-set(LDC_LINKERFLAG_LIST "${SANITIZE_LDFLAGS};${LLVM_LIBRARIES};${LLVM_LDFLAGS}")
+set(LDC_LINKERFLAG_LIST "")
 if(LDC_WITH_LLD)
-    if(MSVC)
-        list(APPEND LDC_LINKERFLAG_LIST lldCOFF.lib lldCore.lib lldDriver.lib)
+    # ELF and Mach-O are only supported starting with LLD 5.0, otherwise there
+    # are command-line option conflicts with LDC.
+    if(LDC_LLVM_VER LESS 500)
+        if(MSVC)
+            list(APPEND LDC_LINKERFLAG_LIST lldDriver.lib lldCOFF.lib lldCore.lib)
+        else()
+            list(APPEND LDC_LINKERFLAG_LIST -llldDriver -llldCOFF -llldCore)
+        endif()
     else()
-        set(LDC_LINKERFLAG_LIST "-llldCOFF;-llldCore;-llldDriver;${LDC_LINKERFLAG_LIST}")
+        if(MSVC)
+            list(APPEND LDC_LINKERFLAG_LIST lldDriver.lib lldCOFF.lib lldELF.lib lldMachO.lib lldYAML.lib lldReaderWriter.lib lldConfig.lib lldCore.lib)
+        else()
+            list(APPEND LDC_LINKERFLAG_LIST -llldDriver -llldCOFF -llldELF -llldMachO -llldYAML -llldReaderWriter -llldConfig -llldCore)
+        endif()
     endif()
 endif()
+list(APPEND LDC_LINKERFLAG_LIST ${SANITIZE_LDFLAGS} ${LLVM_LIBRARIES} ${LLVM_LDFLAGS})
 
 set(LDC_LINK_MANUALLY OFF)
 if(UNIX AND (CMAKE_COMPILER_IS_GNUCXX OR (${CMAKE_CXX_COMPILER_ID} STREQUAL "Clang")))

driver/cl_options-llvm.cpp

@@ -49,3 +49,18 @@ TargetOptions InitTargetOptionsFromCodeGenFlags() {
 std::string getCPUStr() { return ::getCPUStr(); }
 std::string getFeaturesStr() { return ::getFeaturesStr(); }
 } // namespace opts
+
+#if LDC_WITH_LLD && LDC_LLVM_VER >= 500
+// LLD 5.0 uses the shared header too (for LTO) and exposes some wrappers in
+// the lld namespace. Define them here to prevent the LLD object from being
+// linked in with its conflicting command-line options.
+namespace lld {
+TargetOptions InitTargetOptionsFromCodeGenFlags() {
+  return ::InitTargetOptionsFromCodeGenFlags();
+}
+
+CodeModel::Model GetCodeModelFromCMModel() {
+  return CMModel;
+}
+}
+#endif // LDC_WITH_LLD && LDC_LLVM_VER >= 500

driver/linker-gcc.cpp

@@ -21,6 +21,10 @@
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetOptions.h"
 
+#if LDC_WITH_LLD && LDC_LLVM_VER >= 500
+#include "lld/Driver/Driver.h"
+#endif
+
 //////////////////////////////////////////////////////////////////////////////
 
 static llvm::cl::opt<std::string>
@@ -481,7 +485,7 @@ void ArgsBuilder::addTargetFlags() {
 }
 
 //////////////////////////////////////////////////////////////////////////////
-// (Yet unused) specialization for plain ld.
+// Specialization for plain ld.
 
 class LdArgsBuilder : public ArgsBuilder {
   void addSanitizers() override {}
@@ -513,6 +517,28 @@ class LdArgsBuilder : public ArgsBuilder {
 
 int linkObjToBinaryGcc(llvm::StringRef outputPath, bool useInternalLinker,
                        llvm::cl::boolOrDefault fullyStaticFlag) {
+#if LDC_WITH_LLD && LDC_LLVM_VER >= 500
+  if (useInternalLinker) {
+    LdArgsBuilder argsBuilder;
+    argsBuilder.build(outputPath, fullyStaticFlag);
+
+    const auto fullArgs =
+        getFullArgs("ld.lld", argsBuilder.args, global.params.verbose);
+
+    bool success = false;
+    if (global.params.targetTriple->isOSBinFormatELF()) {
+      success = lld::elf::link(fullArgs, /*CanExitEarly*/ false);
+    } else if (global.params.targetTriple->isOSBinFormatMachO()) {
+      success = lld::mach_o::link(fullArgs);
+    }
+
+    if (!success)
+      error(Loc(), "linking with LLD failed");
+
+    return success ? 0 : 1;
+  }
+#endif
+
   // find gcc for linking
   const std::string tool = getGcc();