COFF: Implement DLL symbol exports for bitcode files.

[ruiu]

LGTM

lld/trunk/COFF/InputFiles.cpp

for (unsigned I = 0, E = M->getSymbolCount(); I != E; ++I) {
     StringRef SymName = M->getSymbolName(I);
     int SymbolDef = Attrs & LTO_SYMBOL_DEFINITION_MASK;
     if (SymbolDef == LTO_SYMBOL_DEFINITION_UNDEFINED) {
       SymbolBodies.push_back(new (Alloc) Undefined(SymName));
     } else {
       bool Replaceable = (SymbolDef == LTO_SYMBOL_DEFINITION_TENTATIVE ||
                           (Attrs & LTO_SYMBOL_COMDAT));
       SymbolBodies.push_back(new (Alloc) DefinedBitcode(SymName, Replaceable));
+
+      const llvm::GlobalValue *GV = M->getSymbolGV(I);
+      if (GV && GV->hasDLLExportStorageClass()) {
+        Directives += " /export:";
+        Directives += SymName;
+        if (!GV->getValueType()->isFunctionTy())
+          Directives += ",data";
+      }
     }
   }
 
   // Extract any linker directives from the bitcode file, which are represented
   // as module flags with the key "Linker Options".
   llvm::SmallVector<llvm::Module::ModuleFlagEntry, 8> Flags;
   M->getModule().getModuleFlagsMetadata(Flags);
   for (auto &&Flag : Flags) {

lld/trunk/test/COFF/Inputs/export.ll

+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+define void @_DllMainCRTStartup() {
+  ret void
+}
+
+define void @exportfn1() {
+  ret void
+}
+
+define void @exportfn2() {
+  ret void
+}
+
+define dllexport void @exportfn3() {
+  ret void
+}

lld/trunk/test/COFF/dll.test

 # REQUIRES: winres
 
 # RUN: yaml2obj < %p/Inputs/export.yaml > %t.obj
 # RUN: lld -flavor link2 /out:%t.dll /dll %t.obj /export:exportfn1 /export:exportfn2
 # RUN: llvm-objdump -p %t.dll | FileCheck -check-prefix=EXPORT %s
 
 EXPORT:      Export Table:
 EXPORT:      DLL name: dll.test.tmp.dll
 EXPORT:      Ordinal      RVA  Name
 EXPORT-NEXT:       0        0
 EXPORT-NEXT:       1   0x1008  exportfn1
 EXPORT-NEXT:       2   0x1010  exportfn2
+EXPORT-NEXT:       3   0x1010  exportfn3
+
+# RUN: llvm-as -o %t.lto.obj %p/Inputs/export.ll
+# RUN: lld -flavor link2 /out:%t.lto.dll /dll %t.lto.obj /export:exportfn1 /export:exportfn2
+# RUN: llvm-objdump -p %t.lto.dll | FileCheck -check-prefix=EXPORT-LTO %s
+
+EXPORT-LTO:      Export Table:
+EXPORT-LTO:      DLL name: dll.test.tmp.lto.dll
+EXPORT-LTO:      Ordinal      RVA  Name
+EXPORT-LTO-NEXT:       0        0
+EXPORT-LTO-NEXT:       1   0x1010  exportfn1
+EXPORT-LTO-NEXT:       2   0x1020  exportfn2
+EXPORT-LTO-NEXT:       3   0x1030  exportfn3
 
 # RUN: yaml2obj < %p/Inputs/import.yaml > %t2.obj
 # RUN: lld -flavor link2 /out:%t2.exe %t2.obj %t.lib
 # RUN: llvm-readobj -coff-imports %t2.exe | FileCheck -check-prefix=IMPORT %s
 
+# RUN: lld -flavor link2 /out:%t2.lto.exe %t2.obj %t.lto.lib
+# RUN: llvm-readobj -coff-imports %t2.lto.exe | FileCheck -check-prefix=IMPORT %s
+
 IMPORT: Symbol: exportfn1
 IMPORT: Symbol: exportfn2