Integrate LLD for ELF and Mach-O targets too

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

Author: kinke

CMakeLists.txt

@@ -20,7 +20,7 @@ endif()
 #
 
 find_package(LLVM 3.5 REQUIRED
-    all-targets analysis asmparser asmprinter bitreader bitwriter codegen core debuginfocodeview debuginfodwarf debuginfomsf debuginfopdb globalisel instcombine ipa ipo instrumentation irreader libdriver linker lto mc mcdisassembler mcparser objcarcopts object option profiledata scalaropts selectiondag support tablegen target transformutils vectorize ${EXTRA_LLVM_MODULES})
+    all-targets analysis asmparser asmprinter bitreader bitwriter codegen core debuginfocodeview debuginfodwarf debuginfomsf debuginfopdb globalisel instcombine ipa ipo instrumentation irreader libdriver linker lto mc mcdisassembler mcparser objcarcopts object option passes profiledata scalaropts selectiondag support tablegen target transformutils vectorize ${EXTRA_LLVM_MODULES})
 math(EXPR LDC_LLVM_VER ${LLVM_VERSION_MAJOR}*100+${LLVM_VERSION_MINOR})
 # Remove LLVMTableGen library from list of libraries
 string(REGEX MATCH "^-.*LLVMTableGen[^;]*;|;-.*LLVMTableGen[^;]*" LLVM_TABLEGEN_LIBRARY "${LLVM_LIBRARIES}")
@@ -572,9 +572,9 @@ add_custom_target(${LDMD_EXE} ALL DEPENDS ${LDMD_EXE_FULL})
 set(LDC_LINKERFLAG_LIST "${SANITIZE_LDFLAGS};${LLVM_LIBRARIES};${LLVM_LDFLAGS}")
 if(LDC_WITH_LLD)
     if(MSVC)
-        list(APPEND LDC_LINKERFLAG_LIST lldCOFF.lib lldCore.lib lldDriver.lib)
+        list(APPEND LDC_LINKERFLAG_LIST lldDriver.lib lldCOFF.lib lldELF.lib lldMachO.lib lldYAML.lib lldReaderWriter.lib lldConfig.lib lldCore.lib)
     else()
-        set(LDC_LINKERFLAG_LIST "-llldCOFF;-llldCore;-llldDriver;${LDC_LINKERFLAG_LIST}")
+        set(LDC_LINKERFLAG_LIST "-llldDriver;-llldCOFF;-llldELF;-llldMachO;-llldYAML;-llldReaderWriter;-llldConfig;-llldCore;${LDC_LINKERFLAG_LIST}")
     endif()
 endif()
 

driver/cl_options-llvm.cpp

@@ -100,3 +100,18 @@ std::string getFeaturesStr() {
 }
 #endif // LDC_LLVM_VER < 307
 }
+
+#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

@@ -20,6 +20,10 @@
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetOptions.h"
 
+#if LDC_WITH_LLD
+#include "lld/Driver/Driver.h"
+#endif
+
 //////////////////////////////////////////////////////////////////////////////
 
 static llvm::cl::opt<std::string>
@@ -398,7 +402,7 @@ void ArgsBuilder::addArch() {
 }
 
 //////////////////////////////////////////////////////////////////////////////
-// (Yet unused) specialization for plain ld.
+// Specialization for plain ld.
 
 class LdArgsBuilder : public ArgsBuilder {
   void addSanitizers() override {}
@@ -430,6 +434,33 @@ class LdArgsBuilder : public ArgsBuilder {
 
 int linkObjToBinaryGcc(llvm::StringRef outputPath, bool useInternalLinker,
                        llvm::cl::boolOrDefault fullyStaticFlag) {
+#if LDC_WITH_LLD
+  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
+#if LDC_LLVM_VER >= 400
+                               ,
+                               false // CanExitEarly
+#endif
+      );
+    } 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();