[AArch64] Support COFF linker directives

[mstorsjo]

Summary

This is similar to what was done for ARM in SVN r269574; the code and the test are straight copypaste to the corresponding AArch64 code and test directory.

[mgrang]

LGTM.

lib/Target/AArch64/AArch64AsmPrinter.cpp

 //
 //===----------------------------------------------------------------------===//
 
 #include "AArch64.h"
 #include "AArch64MCInstLower.h"
 #include "AArch64MachineFunctionInfo.h"
 #include "AArch64RegisterInfo.h"
 #include "AArch64Subtarget.h"
+#include "AArch64TargetObjectFile.h"
 #include "InstPrinter/AArch64InstPrinter.h"
 #include "MCTargetDesc/AArch64AddressingModes.h"
 #include "MCTargetDesc/AArch64MCTargetDesc.h"
 #include "Utils/AArch64BaseInfo.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
if (TT.isOSBinFormatMachO()) {
     // Funny Darwin hack: This flag tells the linker that no global symbols
     // contain code that falls through to other global symbols (e.g. the obvious
     // implementation of multiple entry points).  If this doesn't occur, the
     // linker can safely perform dead code stripping.  Since LLVM never
     // generates code that does this, it is always safe to set.
     OutStreamer->EmitAssemblerFlag(MCAF_SubsectionsViaSymbols);
     SM.serializeToStackMapSection();
   }
+
+  if (TT.isOSBinFormatCOFF()) {
+    const auto &TLOF =
+        static_cast<const TargetLoweringObjectFileCOFF &>(getObjFileLowering());
+
+    std::string Flags;
+    raw_string_ostream OS(Flags);
+
+    for (const auto &Function : M)
+      TLOF.emitLinkerFlagsForGlobal(OS, &Function);
+    for (const auto &Global : M.globals())
+      TLOF.emitLinkerFlagsForGlobal(OS, &Global);
+    for (const auto &Alias : M.aliases())
+      TLOF.emitLinkerFlagsForGlobal(OS, &Alias);
+
+    OS.flush();
+
+    // Output collected flags
+    if (!Flags.empty()) {
+      OutStreamer->SwitchSection(TLOF.getDrectveSection());
+      OutStreamer->EmitBytes(Flags);
+    }
+  }
 }
 
 void AArch64AsmPrinter::EmitLOHs() {
   SmallVector<MCSymbol *, 3> MCArgs;
 
   for (const auto &D : AArch64FI->getLOHContainer()) {
     for (const MachineInstr *MI : D.getArgs()) {
       MInstToMCSymbol::iterator LabelIt = LOHInstToLabel.find(MI);

test/CodeGen/AArch64/dllexport.ll

+; RUN: llc -mtriple aarch64-windows-gnu -filetype asm -o - %s | FileCheck %s -check-prefix CHECK -check-prefix CHECK-GNU
+; RUN: llc -mtriple aarch64-windows-msvc -filetype asm -o - %s | FileCheck %s -check-prefix CHECK -check-prefix CHECK-MSVC
+
+define void @f() {
+  ret void
+}
+
+define dllexport void @g() {
+  ret void
+}
+
+define dllexport void @h() unnamed_addr {
+  ret void
+}
+
+declare dllexport void @i()
+
+define linkonce_odr dllexport void @j() {
+  ret void
+}
+
+define linkonce_odr dllexport void @k() alwaysinline {
+  ret void
+}
+
+define weak_odr dllexport void @l() {
+  ret void
+}
+
+@m = dllexport global i32 0, align 4
+@n = dllexport unnamed_addr constant i32 0
+@o = common dllexport global i32 0, align 4
+@p = weak_odr dllexport global i32 0, align 4
+@q = weak_odr dllexport unnamed_addr constant i32 0
+
+@r = dllexport alias void (), void () * @f
+@s = dllexport alias void (), void () * @g
+@t = dllexport alias void (), void () * @f
+@u = weak_odr dllexport alias void (), void () * @g
+
+; CHECK: .section .drectve
+; CHECK-GNU-NOT: -export:f
+; CHECK-GNU: -export:g
+; CHECK-GNU-SAME: -export:h
+; CHECK-GNU-NOT: -export:i
+; CHECK-GNU-SAME: -export:j
+; CHECK-GNU-SAME: -export:k
+; CHECK-GNU-SAME: -export:l
+; CHECK-GNU-SAME: -export:m,data
+; CHECK-GNU-SAME: -export:n,data
+; CHECK-GNU-SAME: -export:o,data
+; CHECK-GNU-SAME: -export:p,data
+; CHECK-GNU-SAME: -export:q,data
+; CHECK-GNU-SAME: -export:r
+; CHECK-GNU-SAME: -export:s
+; CHECK-GNU-SAME: -export:t
+; CHECK-GNU-SAME: -export:u
+; CHECK-MSVC-NOT: /EXPORT:f
+; CHECK-MSVC: /EXPORT:g
+; CHECK-MSVC-SAME: /EXPORT:h
+; CHECK-MSVC-NOT: /EXPORT:i
+; CHECK-MSVC-SAME: /EXPORT:j
+; CHECK-MSVC-SAME: /EXPORT:k
+; CHECK-MSVC-SAME: /EXPORT:l
+; CHECK-MSVC-SAME: /EXPORT:m,DATA
+; CHECK-MSVC-SAME: /EXPORT:n,DATA
+; CHECK-MSVC-SAME: /EXPORT:o,DATA
+; CHECK-MSVC-SAME: /EXPORT:p,DATA
+; CHECK-MSVC-SAME: /EXPORT:q,DATA
+; CHECK-MSVC-SAME: /EXPORT:r
+; CHECK-MSVC-SAME: /EXPORT:s
+; CHECK-MSVC-SAME: /EXPORT:t
+; CHECK-MSVC-SAME: /EXPORT:u
+