diff --git a/llvm/include/llvm/MC/MCObjectStreamer.h b/llvm/include/llvm/MC/MCObjectStreamer.h
--- a/llvm/include/llvm/MC/MCObjectStreamer.h
+++ b/llvm/include/llvm/MC/MCObjectStreamer.h
@@ -50,6 +50,16 @@
   };
   SmallVector<PendingMCFixup, 2> PendingFixups;
 
+  struct PendingAssignment {
+    MCSymbol *Symbol;
+    const MCExpr *Value;
+  };
+
+  /// A list of conditional assignments we may need to emit if the target
+  /// symbol is later emitted.
+  DenseMap<const MCSymbol *, SmallVector<PendingAssignment, 1>>
+      pendingAssignments;
+
   virtual void emitInstToData(const MCInst &Inst, const MCSubtargetInfo&) = 0;
   void emitCFIStartProcImpl(MCDwarfFrameInfo &Frame) override;
   void emitCFIEndProcImpl(MCDwarfFrameInfo &Frame) override;
@@ -118,6 +128,8 @@
   virtual void emitLabelAtPos(MCSymbol *Symbol, SMLoc Loc, MCFragment *F,
                               uint64_t Offset);
   void emitAssignment(MCSymbol *Symbol, const MCExpr *Value) override;
+  void emitConditionalAssignment(MCSymbol *Symbol,
+                                 const MCExpr *Value) override;
   void emitValueImpl(const MCExpr *Value, unsigned Size,
                      SMLoc Loc = SMLoc()) override;
   void emitULEB128Value(const MCExpr *Value) override;
@@ -208,6 +220,10 @@
                                        const MCSymbol *Lo) override;
 
   bool mayHaveInstructions(MCSection &Sec) const override;
+
+  /// Emits pending conditional assignments that depend on \p Symbol
+  /// being emitted.
+  void emitPendingAssignments(MCSymbol *Symbol);
 };
 
 } // end namespace llvm
diff --git a/llvm/include/llvm/MC/MCStreamer.h b/llvm/include/llvm/MC/MCStreamer.h
--- a/llvm/include/llvm/MC/MCStreamer.h
+++ b/llvm/include/llvm/MC/MCStreamer.h
@@ -524,6 +524,10 @@
   /// \param Value - The value for the symbol.
   virtual void emitAssignment(MCSymbol *Symbol, const MCExpr *Value);
 
+  /// Emit an assignment of \p Value to \p Symbol, but only if \p Value is also
+  /// emitted.
+  virtual void emitConditionalAssignment(MCSymbol *Symbol, const MCExpr *Value);
+
   /// Emit an weak reference from \p Alias to \p Symbol.
   ///
   /// This corresponds to an assembler statement such as:
diff --git a/llvm/lib/MC/MCAsmStreamer.cpp b/llvm/lib/MC/MCAsmStreamer.cpp
--- a/llvm/lib/MC/MCAsmStreamer.cpp
+++ b/llvm/lib/MC/MCAsmStreamer.cpp
@@ -174,6 +174,8 @@
   void emitThumbFunc(MCSymbol *Func) override;
 
   void emitAssignment(MCSymbol *Symbol, const MCExpr *Value) override;
+  void emitConditionalAssignment(MCSymbol *Symbol,
+                                 const MCExpr *Value) override;
   void emitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) override;
   bool emitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
 
@@ -679,6 +681,15 @@
   MCStreamer::emitAssignment(Symbol, Value);
 }
 
+void MCAsmStreamer::emitConditionalAssignment(MCSymbol *Symbol,
+                                              const MCExpr *Value) {
+  OS << ".lto_set_conditional ";
+  Symbol->print(OS, MAI);
+  OS << ", ";
+  Value->print(OS, MAI);
+  EmitEOL();
+}
+
 void MCAsmStreamer::emitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
   OS << ".weakref ";
   Alias->print(OS, MAI);
diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -281,6 +281,18 @@
     Symbol->setOffset(0);
     addPendingLabel(Symbol);
   }
+
+  emitPendingAssignments(Symbol);
+}
+
+void MCObjectStreamer::emitPendingAssignments(MCSymbol *Symbol) {
+  auto Assignments = pendingAssignments.find(Symbol);
+  if (Assignments != pendingAssignments.end()) {
+    for (const auto &A : Assignments->second)
+      emitAssignment(A.Symbol, A.Value);
+
+    pendingAssignments.erase(Assignments);
+  }
 }
 
 // Emit a label at a previously emitted fragment/offset position. This must be
@@ -353,6 +365,19 @@
 void MCObjectStreamer::emitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
   getAssembler().registerSymbol(*Symbol);
   MCStreamer::emitAssignment(Symbol, Value);
+  emitPendingAssignments(Symbol);
+}
+
+void MCObjectStreamer::emitConditionalAssignment(MCSymbol *Symbol,
+                                                 const MCExpr *Value) {
+  const MCSymbol *Target = &cast<MCSymbolRefExpr>(*Value).getSymbol();
+
+  // If the symbol already exists, emit the assignment. Otherwise, emit it
+  // later only if the symbol is also emitted.
+  if (Target->isRegistered())
+    emitAssignment(Symbol, Value);
+  else
+    pendingAssignments[Target].push_back({Symbol, Value});
 }
 
 bool MCObjectStreamer::mayHaveInstructions(MCSection &Sec) const {
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -356,8 +356,14 @@
   /// return the contents from the current token up to the end or comma.
   StringRef parseStringToComma();
 
-  bool parseAssignment(StringRef Name, bool allow_redef,
-                       bool NoDeadStrip = false);
+  enum class AssignmentKind {
+    Set,
+    Equiv,
+    Equal,
+    LTOSetConditional,
+  };
+
+  bool parseAssignment(StringRef Name, AssignmentKind Kind);
 
   unsigned getBinOpPrecedence(AsmToken::TokenKind K,
                               MCBinaryExpr::Opcode &Kind);
@@ -534,6 +540,7 @@
     DK_ADDRSIG_SYM,
     DK_PSEUDO_PROBE,
     DK_LTO_DISCARD,
+    DK_LTO_SET_CONDITIONAL,
     DK_END
   };
 
@@ -564,8 +571,8 @@
                                const fltSemantics &); // ".single", ...
   bool parseDirectiveFill(); // ".fill"
   bool parseDirectiveZero(); // ".zero"
-  // ".set", ".equ", ".equiv"
-  bool parseDirectiveSet(StringRef IDVal, bool allow_redef);
+  // ".set", ".equ", ".equiv", ".lto_set_conditional"
+  bool parseDirectiveSet(StringRef IDVal, AssignmentKind Kind);
   bool parseDirectiveOrg(); // ".org"
   // ".align{,32}", ".p2align{,w,l}"
   bool parseDirectiveAlign(bool IsPow2, unsigned ValueSize);
@@ -1968,7 +1975,7 @@
     // identifier '=' ... -> assignment statement
     Lex();
 
-    return parseAssignment(IDVal, true);
+    return parseAssignment(IDVal, AssignmentKind::Equal);
 
   default: // Normal instruction or directive.
     break;
@@ -2027,9 +2034,11 @@
       break;
     case DK_SET:
     case DK_EQU:
-      return parseDirectiveSet(IDVal, true);
+      return parseDirectiveSet(IDVal, AssignmentKind::Set);
     case DK_EQUIV:
-      return parseDirectiveSet(IDVal, false);
+      return parseDirectiveSet(IDVal, AssignmentKind::Equiv);
+    case DK_LTO_SET_CONDITIONAL:
+      return parseDirectiveSet(IDVal, AssignmentKind::LTOSetConditional);
     case DK_ASCII:
       return parseDirectiveAscii(IDVal, false);
     case DK_ASCIZ:
@@ -2925,11 +2934,13 @@
   ActiveMacros.pop_back();
 }
 
-bool AsmParser::parseAssignment(StringRef Name, bool allow_redef,
-                                bool NoDeadStrip) {
+bool AsmParser::parseAssignment(StringRef Name, AssignmentKind Kind) {
   MCSymbol *Sym;
   const MCExpr *Value;
-  if (MCParserUtils::parseAssignmentExpression(Name, allow_redef, *this, Sym,
+  SMLoc ExprLoc = getTok().getLoc();
+  bool AllowRedef =
+      Kind == AssignmentKind::Set || Kind == AssignmentKind::Equal;
+  if (MCParserUtils::parseAssignmentExpression(Name, AllowRedef, *this, Sym,
                                                Value))
     return true;
 
@@ -2944,9 +2955,22 @@
     return false;
 
   // Do the assignment.
-  Out.emitAssignment(Sym, Value);
-  if (NoDeadStrip)
+  switch (Kind) {
+  case AssignmentKind::Equal:
+    Out.emitAssignment(Sym, Value);
+    break;
+  case AssignmentKind::Set:
+  case AssignmentKind::Equiv:
+    Out.emitAssignment(Sym, Value);
     Out.emitSymbolAttribute(Sym, MCSA_NoDeadStrip);
+    break;
+  case AssignmentKind::LTOSetConditional:
+    if (Value->getKind() != MCExpr::SymbolRef)
+      return Error(ExprLoc, "expected identifier");
+
+    Out.emitConditionalAssignment(Sym, Value);
+    break;
+  }
 
   return false;
 }
@@ -2998,10 +3022,11 @@
 ///   ::= .equ identifier ',' expression
 ///   ::= .equiv identifier ',' expression
 ///   ::= .set identifier ',' expression
-bool AsmParser::parseDirectiveSet(StringRef IDVal, bool allow_redef) {
+///   ::= .lto_set_conditional identifier ',' expression
+bool AsmParser::parseDirectiveSet(StringRef IDVal, AssignmentKind Kind) {
   StringRef Name;
   if (check(parseIdentifier(Name), "expected identifier") || parseComma() ||
-      parseAssignment(Name, allow_redef, true))
+      parseAssignment(Name, Kind))
     return true;
   return false;
 }
@@ -5581,6 +5606,7 @@
   DirectiveKindMap[".addrsig_sym"] = DK_ADDRSIG_SYM;
   DirectiveKindMap[".pseudoprobe"] = DK_PSEUDO_PROBE;
   DirectiveKindMap[".lto_discard"] = DK_LTO_DISCARD;
+  DirectiveKindMap[".lto_set_conditional"] = DK_LTO_SET_CONDITIONAL;
 }
 
 MCAsmMacro *AsmParser::parseMacroLikeBody(SMLoc DirectiveLoc) {
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -431,6 +431,9 @@
     TS->emitLabel(Symbol);
 }
 
+void MCStreamer::emitConditionalAssignment(MCSymbol *Symbol,
+                                           const MCExpr *Value) {}
+
 void MCStreamer::emitCFISections(bool EH, bool Debug) {}
 
 void MCStreamer::emitCFIStartProc(bool IsSimple, SMLoc Loc) {
diff --git a/llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp b/llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
--- a/llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
+++ b/llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
@@ -87,7 +87,8 @@
     if (isa<Function>(&ExportGV) && allowPromotionAlias(OldName)) {
       // Create a local alias with the original name to avoid breaking
       // references from inline assembly.
-      std::string Alias = ".set " + OldName + "," + NewName + "\n";
+      std::string Alias =
+          ".lto_set_conditional " + OldName + "," + NewName + "\n";
       ExportM.appendModuleInlineAsm(Alias);
     }
   }
diff --git a/llvm/test/MC/ELF/lto-set-conditional.s b/llvm/test/MC/ELF/lto-set-conditional.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/ELF/lto-set-conditional.s
@@ -0,0 +1,51 @@
+# RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu < %s | llvm-readobj --symbols - | FileCheck %s
+# RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu --defsym ERR=1 %s 2>&1 |\
+# RUN:         FileCheck %s --check-prefix=ERR
+
+.byte 0
+
+.lto_set_conditional b, a
+.lto_set_conditional d, a
+.lto_set_conditional c, b
+.lto_set_conditional e, n
+
+# CHECK:      Symbol {
+# CHECK:        Name: a
+# CHECK-NEXT:   Value: 0x1
+a:
+.byte 0
+
+# Verify that pending conditional symbols are emitted next
+
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: b
+# CHECK-NEXT:   Value: 0x1
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: c
+# CHECK-NEXT:   Value: 0x1
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: d
+# CHECK-NEXT:   Value: 0x1
+
+# CHECK-NOT:    Name: e
+
+# Remaining conditional symbols are emitted immediately
+
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: f
+# CHECK-NEXT:   Value: 0x1
+.lto_set_conditional f, a
+
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: g
+# CHECK-NEXT:   Value: 0x1
+.lto_set_conditional g, b
+
+# CHECK-NOT:   Name: h
+.lto_set_conditional h, m
+
+.ifdef ERR
+.text
+# ERR: {{.*}}.s:[[#@LINE+1]]:25: error: expected identifier
+.lto_set_conditional i, ERR
+.endif
diff --git a/llvm/test/MC/MachO/lto-set-conditional.s b/llvm/test/MC/MachO/lto-set-conditional.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/MachO/lto-set-conditional.s
@@ -0,0 +1,75 @@
+# RUN: llvm-mc -filetype=obj -triple i386-apple-darwin9 < %s | llvm-readobj --symbols - | FileCheck %s
+# RUN: not llvm-mc -filetype=obj -triple i386-apple-darwin9 --defsym ERR=1 %s 2>&1 |\
+# RUN:         FileCheck %s --check-prefix=ERR
+
+.byte 0
+
+.lto_set_conditional b, a
+.lto_set_conditional d, a
+.lto_set_conditional c, b
+.lto_set_conditional e, n
+
+# CHECK:      Symbol {
+# CHECK:        Name: a
+# CHECK:        Flags [
+# CHECK-NEXT:     NoDeadStrip
+# CHECK:        Value: 0x1
+a:
+.byte 0
+.no_dead_strip a
+
+# Verify that pending conditional symbols are emitted next
+
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: b
+# CHECK:        Flags [
+# CHECK-NEXT:     NoDeadStrip
+# CHECK:        Value: 0x1
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: c
+# CHECK:        Flags [
+# CHECK-NEXT:     NoDeadStrip
+# CHECK:        Value: 0x1
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: d
+# CHECK:        Flags [
+# CHECK-NEXT:     NoDeadStrip
+# CHECK:        Value: 0x1
+
+# CHECK-NOT:    Name: e
+
+# Remaining conditional symbols are emitted immediately
+
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: f
+# CHECK:        Flags [
+# CHECK-NEXT:     NoDeadStrip
+# CHECK:        Value: 0x1
+.lto_set_conditional f, a
+
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: g
+# CHECK:        Flags [
+# CHECK-NEXT:     NoDeadStrip
+# CHECK:        Value: 0x1
+.lto_set_conditional g, b
+
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: m
+# CHECK:        Flags [
+# CHECK-NOT :     NoDeadStrip
+# CHECK:        Value: 0x2
+m:
+
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: h
+# CHECK:        Flags [
+# CHECK-NOT :     NoDeadStrip
+# CHECK:        Value: 0x2
+.lto_set_conditional h, m
+
+.ifdef ERR
+.text
+# ERR: {{.*}}.s:[[#@LINE+1]]:25: error: expected identifier
+.lto_set_conditional i, ERR
+.endif
diff --git a/llvm/test/ThinLTO/X86/devirt2.ll b/llvm/test/ThinLTO/X86/devirt2.ll
--- a/llvm/test/ThinLTO/X86/devirt2.ll
+++ b/llvm/test/ThinLTO/X86/devirt2.ll
@@ -131,12 +131,10 @@
 ; RUN:   -r=%t1.o,_ZN1D1mEi, \
 ; RUN:   -r=%t1.o,test2, \
 ; RUN:   -r=%t2.o,_ZN1A1nEi,p \
-; RUN:   -r=%t2.o,_ZN1A1nEi, \
 ; RUN:   -r=%t2.o,_ZN1B1fEi,p \
 ; RUN:   -r=%t2.o,_ZN1C1fEi,p \
 ; RUN:   -r=%t2.o,_ZN1D1mEi,p \
 ; RUN:   -r=%t2.o,_ZN1E1mEi,p \
-; RUN:   -r=%t2.o,_ZN1E1mEi, \
 ; RUN:   -r=%t2.o,_ZTV1B, \
 ; RUN:   -r=%t2.o,_ZTV1C, \
 ; RUN:   -r=%t2.o,_ZTV1D, \
@@ -169,12 +167,10 @@
 ; RUN:   -r=%t1.o,_ZN1D1mEi, \
 ; RUN:   -r=%t1.o,test2, \
 ; RUN:   -r=%t2.o,_ZN1A1nEi,p \
-; RUN:   -r=%t2.o,_ZN1A1nEi, \
 ; RUN:   -r=%t2.o,_ZN1B1fEi,p \
 ; RUN:   -r=%t2.o,_ZN1C1fEi,p \
 ; RUN:   -r=%t2.o,_ZN1D1mEi,p \
 ; RUN:   -r=%t2.o,_ZN1E1mEi,p \
-; RUN:   -r=%t2.o,_ZN1E1mEi, \
 ; RUN:   -r=%t2.o,_ZTV1B, \
 ; RUN:   -r=%t2.o,_ZTV1C, \
 ; RUN:   -r=%t2.o,_ZTV1D, \
diff --git a/llvm/test/Transforms/ThinLTOBitcodeWriter/cfi-icall-static-inline-asm.ll b/llvm/test/Transforms/ThinLTOBitcodeWriter/cfi-icall-static-inline-asm.ll
--- a/llvm/test/Transforms/ThinLTOBitcodeWriter/cfi-icall-static-inline-asm.ll
+++ b/llvm/test/Transforms/ThinLTOBitcodeWriter/cfi-icall-static-inline-asm.ll
@@ -3,7 +3,7 @@
 
 target triple = "x86_64-unknown-linux-gnu"
 
-; CHECK: module asm ".set a,a.[[HASH:[0-9a-f]+]]"
+; CHECK: module asm ".lto_set_conditional a,a.[[HASH:[0-9a-f]+]]"
 
 define void @b() {
   %f = alloca void ()*, align 8