Index: llvm/include/llvm/MC/MCAsmInfo.h
===================================================================
--- llvm/include/llvm/MC/MCAsmInfo.h
+++ llvm/include/llvm/MC/MCAsmInfo.h
@@ -322,9 +322,10 @@
   /// symbol that can be hidden (unexported).  Defaults to false.
   bool HasWeakDefCanBeHiddenDirective = false;
 
-  /// True if we have a .linkonce directive.  This is used on cygwin/mingw.
+  /// True if we should mark symbols as global instead of weak, for
+  /// weak*/linkonce*, if the symbol has a comdat.
   /// Defaults to false.
-  bool HasLinkOnceDirective = false;
+  bool AvoidWeakIfComdat = false;
 
   /// True if we have a .lglobl directive, which is used to emit the information
   /// of a static symbol into the symbol table. Defaults to false.
@@ -590,7 +591,7 @@
     return HasWeakDefCanBeHiddenDirective;
   }
 
-  bool hasLinkOnceDirective() const { return HasLinkOnceDirective; }
+  bool avoidWeakIfComdat() const { return AvoidWeakIfComdat; }
 
   bool hasDotLGloblDirective() const { return HasDotLGloblDirective; }
 
Index: llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -414,7 +414,7 @@
         OutStreamer->emitSymbolAttribute(GVSym, MCSA_WeakDefinition);
       else
         OutStreamer->emitSymbolAttribute(GVSym, MCSA_WeakDefAutoPrivate);
-    } else if (MAI->hasLinkOnceDirective()) {
+    } else if (MAI->avoidWeakIfComdat() && GV->hasComdat()) {
       // .globl _foo
       OutStreamer->emitSymbolAttribute(GVSym, MCSA_Global);
       //NOTE: linkonce is handled by the section the symbol was assigned to.
Index: llvm/lib/MC/MCAsmInfoCOFF.cpp
===================================================================
--- llvm/lib/MC/MCAsmInfoCOFF.cpp
+++ llvm/lib/MC/MCAsmInfoCOFF.cpp
@@ -26,7 +26,7 @@
   HasDotTypeDotSizeDirective = false;
   HasSingleParameterDotFile = true;
   WeakRefDirective = "\t.weak\t";
-  HasLinkOnceDirective = true;
+  AvoidWeakIfComdat = true;
 
   // Doesn't support visibility:
   HiddenVisibilityAttr = HiddenDeclarationVisibilityAttr = MCSA_Invalid;
Index: llvm/test/CodeGen/X86/coff-linkonce.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/coff-linkonce.ll
@@ -0,0 +1,9 @@
+; RUN: llc -function-sections -o - %s | FileCheck %s
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+; CHECK: .section{{.*}}one_only
+define linkonce_odr void @foo() {
+  ret void
+}
Index: llvm/test/CodeGen/X86/coff-weak.ll
===================================================================
--- llvm/test/CodeGen/X86/coff-weak.ll
+++ llvm/test/CodeGen/X86/coff-weak.ll
@@ -1,9 +1,50 @@
-; RUN: llc -function-sections -o - %s | FileCheck %s
+; RUN: llc -mtriple=i686-windows-msvc -o - %s | FileCheck -check-prefix=X86 %s
+; RUN: llc -mtriple=x86_64-windows-msvc -o - %s | FileCheck -check-prefix=X64 %s
 
-target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
-target triple = "x86_64-pc-windows-msvc"
+; X86: .weak _foo
+; X64: .weak foo
+define weak void @foo() {
+  ret void
+}
+
+; X86: .weak _bar
+; X64: .weak bar
+define weak_odr void @bar() {
+  ret void
+}
+
+; X86-NOT: .weak _bar_comdat
+; X64-NOT: .weak bar_comdat
+$bar_comdat = comdat any
+
+define weak_odr void @bar_comdat() comdat {
+  ret void
+}
+
+; X86: .weak _baz
+; X64: .weak baz
+define linkonce void @baz() {
+  ret void
+}
+
+; X86-NOT: .weak _baz_comdat
+; X64-NOT: .weak baz_comdat
+$baz_comdat = comdat any
+
+define linkonce void @baz_comdat() comdat {
+  ret void
+}
+
+; X86: .weak _quux
+; X64: .weak quux
+define linkonce_odr void @quux() {
+  ret void
+}
+
+; X86-NOT: .weak _quux_comdat
+; X64-NOT: .weak quux_comdat
+$quux_comdat = comdat any
 
-; CHECK: .section{{.*}}one_only
-define linkonce_odr void @foo() {
+define linkonce_odr void @quux_comdat() comdat {
   ret void
 }
Index: llvm/test/CodeGen/X86/dllexport-x86_64.ll
===================================================================
--- llvm/test/CodeGen/X86/dllexport-x86_64.ll
+++ llvm/test/CodeGen/X86/dllexport-x86_64.ll
@@ -20,16 +20,20 @@
 }
 
 ; CHECK: .globl lnk1
-define linkonce_odr dllexport void @lnk1() {
+$lnk1 = comdat any
+
+define linkonce_odr dllexport void @lnk1() comdat {
 	ret void
 }
 
 ; CHECK: .globl lnk2
-define linkonce_odr dllexport void @lnk2() alwaysinline {
+$lnk2 = comdat any
+
+define linkonce_odr dllexport void @lnk2() alwaysinline comdat {
 	ret void
 }
 
-; CHECK: .globl weak1
+; CHECK: .weak weak1
 define weak_odr dllexport void @weak1() {
 	ret void
 }
@@ -46,14 +50,14 @@
 ; CHECK: .comm Var3
 @Var3 = common dllexport global i32 0, align 4
 
-; CHECK: .globl WeakVar1
+; CHECK: .weak WeakVar1
 @WeakVar1 = weak_odr dllexport global i32 1, align 4
 
-; CHECK: .globl WeakVar2
+; CHECK: .weak WeakVar2
 @WeakVar2 = weak_odr dllexport unnamed_addr constant i32 1
 
 ; CHECK: .bss
-; CHECK: .globl WeakVar3
+; CHECK: .weak WeakVar3
 @WeakVar3 = weak_odr dllexport global i32 0, align 4
 
 
Index: llvm/test/CodeGen/X86/dllexport.ll
===================================================================
--- llvm/test/CodeGen/X86/dllexport.ll
+++ llvm/test/CodeGen/X86/dllexport.ll
@@ -45,16 +45,20 @@
 }
 
 ; CHECK: .globl _lnk1
-define linkonce_odr dllexport void @lnk1() {
+$lnk1 = comdat any
+
+define linkonce_odr dllexport void @lnk1() comdat {
 	ret void
 }
 
 ; CHECK: .globl _lnk2
-define linkonce_odr dllexport void @lnk2() alwaysinline {
+$lnk2 = comdat any
+
+define linkonce_odr dllexport void @lnk2() alwaysinline comdat {
 	ret void
 }
 
-; CHECK: .globl _weak1
+; CHECK: .weak _weak1
 define weak_odr dllexport void @weak1() {
 	ret void
 }
@@ -71,10 +75,10 @@
 ; CHECK: .comm _Var3
 @Var3 = common dllexport global i32 0, align 4
 
-; CHECK: .globl _WeakVar1
+; CHECK: .weak _WeakVar1
 @WeakVar1 = weak_odr dllexport global i32 1, align 4
 
-; CHECK: .globl _WeakVar2
+; CHECK: .weak _WeakVar2
 @WeakVar2 = weak_odr dllexport unnamed_addr constant i32 1