Index: lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.h
===================================================================
--- lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.h
+++ lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.h
@@ -38,6 +38,10 @@
   explicit AArch64MCAsmInfoCOFF();
 };
 
+struct AArch64MCAsmInfoCOFFGNU : public AArch64MCAsmInfoCOFF {
+  explicit AArch64MCAsmInfoCOFFGNU();
+};
+
 } // namespace llvm
 
 #endif
Index: lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
===================================================================
--- lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
+++ lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
@@ -109,3 +109,7 @@
   SupportsDebugInformation = true;
   ExceptionsType = ExceptionHandling::WinEH;
 }
+
+AArch64MCAsmInfoCOFFGNU::AArch64MCAsmInfoCOFFGNU() {
+  CommentString = "//";
+}
Index: lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp
===================================================================
--- lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp
+++ lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp
@@ -69,6 +69,8 @@
   MCAsmInfo *MAI;
   if (TheTriple.isOSBinFormatMachO())
     MAI = new AArch64MCAsmInfoDarwin();
+  else if (TheTriple.isOSBinFormatCOFF() && TheTriple.isGNUEnvironment())
+    MAI = new AArch64MCAsmInfoCOFFGNU();
   else if (TheTriple.isOSBinFormatCOFF())
     MAI = new AArch64MCAsmInfoCOFF();
   else {
Index: test/MC/AArch64/coff-gnu.s
===================================================================
--- /dev/null
+++ test/MC/AArch64/coff-gnu.s
@@ -0,0 +1,11 @@
+// RUN: llvm-mc -triple aarch64-windows-gnu -filetype obj -o %t.obj %s
+// RUN: llvm-objdump -d %t.obj | FileCheck %s
+
+func:
+// Check that the nop instruction after the semicolon also is handled
+nop; nop
+add x0, x0, #42
+
+// CHECK:  0:       1f 20 03 d5     nop
+// CHECK:  4:       1f 20 03 d5     nop
+// CHECK:  8:       00 a8 00 91     add x0, x0, #42