diff --git a/llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h b/llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
--- a/llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
+++ b/llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
@@ -136,6 +136,7 @@
   bool removeDeadStuffFromFunction(Function *F);
   bool deleteDeadVarargs(Function &F);
   bool removeDeadArgumentsFromCallers(Function &F);
+  void propagateVirtMustcallLiveness(const Module &M);
 };
 
 } // end namespace llvm
diff --git a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
--- a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -85,6 +85,11 @@
   virtual bool shouldHackArguments() const { return false; }
 };
 
+bool isMustTailCalleeAnalyzable(const CallBase &CB) {
+  assert(CB.isMustTailCall());
+  return CB.getCalledFunction() && !CB.getCalledFunction()->isDeclaration();
+}
+
 } // end anonymous namespace
 
 char DAE::ID = 0;
@@ -520,8 +525,16 @@
   for (const BasicBlock &BB : F) {
     // If we have any returns of `musttail` results - the signature can't
     // change
-    if (BB.getTerminatingMustTailCall() != nullptr)
+    if (const auto *TC = BB.getTerminatingMustTailCall()) {
       HasMustTailCalls = true;
+      // In addition, if the called function is not locally defined (or unknown,
+      // if this is an indirect call), we can't change the callsite and thus
+      // can't change this function's signature either.
+      if (!isMustTailCalleeAnalyzable(*TC)) {
+        markLive(F);
+        return;
+      }
+    }
   }
 
   if (HasMustTailCalls) {
@@ -1081,6 +1094,26 @@
   return true;
 }
 
+void DeadArgumentEliminationPass::propagateVirtMustcallLiveness(
+    const Module &M) {
+  // If a function was marked "live", and it has musttail callers, they in turn
+  // can't change either.
+  LiveFuncSet NewLiveFuncs(LiveFunctions);
+  while (!NewLiveFuncs.empty()) {
+    LiveFuncSet Temp;
+    for (const auto *F : NewLiveFuncs)
+      for (const auto *U : F->users())
+        if (const auto *CB = dyn_cast<CallBase>(U))
+          if (CB->isMustTailCall())
+            if (!LiveFunctions.count(CB->getParent()->getParent()))
+              Temp.insert(CB->getParent()->getParent());
+    NewLiveFuncs.clear();
+    NewLiveFuncs.insert(Temp.begin(), Temp.end());
+    for (const auto *F : Temp)
+      markLive(*F);
+  }
+}
+
 PreservedAnalyses DeadArgumentEliminationPass::run(Module &M,
                                                    ModuleAnalysisManager &) {
   bool Changed = false;
@@ -1101,6 +1134,8 @@
   for (auto &F : M)
     surveyFunction(F);
 
+  propagateVirtMustcallLiveness(M);
+
   // Now, remove all dead arguments and return values from each function in
   // turn.  We use make_early_inc_range here because functions will probably get
   // removed (i.e. replaced by new ones).
diff --git a/llvm/test/Transforms/DeadArgElim/2010-04-30-DbgInfo.ll b/llvm/test/Transforms/DeadArgElim/2010-04-30-DbgInfo.ll
--- a/llvm/test/Transforms/DeadArgElim/2010-04-30-DbgInfo.ll
+++ b/llvm/test/Transforms/DeadArgElim/2010-04-30-DbgInfo.ll
@@ -8,12 +8,21 @@
 
 define ptr @vfs_addname(ptr %name, i32 %len, i32 %hash, i32 %flags) nounwind ssp !dbg !1 {
 ;
+; CHECK-LABEL: define {{[^@]+}}@vfs_addname
+; CHECK-SAME: (ptr [[NAME:%.*]], i32 [[LEN:%.*]], i32 [[HASH:%.*]], i32 [[FLAGS:%.*]]) #[[ATTR0:[0-9]+]] !dbg [[DBG4:![0-9]+]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata ptr [[NAME]], metadata [[META11:![0-9]+]], metadata !DIExpression()), !dbg [[DBG12:![0-9]+]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[LEN]], metadata [[META13:![0-9]+]], metadata !DIExpression()), !dbg [[DBG12]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[HASH]], metadata [[META14:![0-9]+]], metadata !DIExpression()), !dbg [[DBG12]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[FLAGS]], metadata [[META15:![0-9]+]], metadata !DIExpression()), !dbg [[DBG12]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call fastcc ptr @add_name_internal(ptr [[NAME]], i32 [[HASH]]) #[[ATTR3:[0-9]+]], !dbg [[DBG16:![0-9]+]]
+; CHECK-NEXT:    ret ptr [[TMP0]], !dbg [[DBG16]]
+;
 entry:
   call void @llvm.dbg.value(metadata ptr %name, metadata !0, metadata !DIExpression()), !dbg !DILocation(scope: !1)
   call void @llvm.dbg.value(metadata i32 %len, metadata !10, metadata !DIExpression()), !dbg !DILocation(scope: !1)
   call void @llvm.dbg.value(metadata i32 %hash, metadata !11, metadata !DIExpression()), !dbg !DILocation(scope: !1)
   call void @llvm.dbg.value(metadata i32 %flags, metadata !12, metadata !DIExpression()), !dbg !DILocation(scope: !1)
-; CHECK:  call fastcc ptr @add_name_internal(ptr %name, i32 %hash) [[NUW:#[0-9]+]], !dbg !{{[0-9]+}}
   %0 = call fastcc ptr @add_name_internal(ptr %name, i32 %len, i32 %hash, i8 zeroext 0, i32 %flags) nounwind, !dbg !13 ; <ptr> [#uses=1]
   ret ptr %0, !dbg !13
 }
@@ -22,6 +31,24 @@
 
 define internal fastcc ptr @add_name_internal(ptr %name, i32 %len, i32 %hash, i8 zeroext %extra, i32 %flags) noinline nounwind ssp !dbg !16 {
 ;
+; CHECK-LABEL: define {{[^@]+}}@add_name_internal
+; CHECK-SAME: (ptr [[NAME:%.*]], i32 [[HASH:%.*]]) #[[ATTR2:[0-9]+]] !dbg [[DBG18:![0-9]+]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata ptr [[NAME]], metadata [[META22:![0-9]+]], metadata !DIExpression()), !dbg [[DBG23:![0-9]+]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 poison, metadata [[META24:![0-9]+]], metadata !DIExpression()), !dbg [[DBG23]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[HASH]], metadata [[META25:![0-9]+]], metadata !DIExpression()), !dbg [[DBG23]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i8 poison, metadata [[META26:![0-9]+]], metadata !DIExpression()), !dbg [[DBG23]]
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 poison, metadata [[META27:![0-9]+]], metadata !DIExpression()), !dbg [[DBG23]]
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp eq i32 [[HASH]], 0, !dbg [[DBG28:![0-9]+]]
+; CHECK-NEXT:    br i1 [[TMP0]], label [[BB:%.*]], label [[BB1:%.*]], !dbg [[DBG28]]
+; CHECK:       bb:
+; CHECK-NEXT:    br label [[BB2:%.*]], !dbg [[DBG30:![0-9]+]]
+; CHECK:       bb1:
+; CHECK-NEXT:    br label [[BB2]], !dbg [[DBG31:![0-9]+]]
+; CHECK:       bb2:
+; CHECK-NEXT:    [[DOT0:%.*]] = phi ptr [ @.str, [[BB]] ], [ [[NAME]], [[BB1]] ]
+; CHECK-NEXT:    ret ptr [[DOT0]], !dbg [[DBG31]]
+;
 entry:
   call void @llvm.dbg.value(metadata ptr %name, metadata !15, metadata !DIExpression()), !dbg !DILocation(scope: !16)
   call void @llvm.dbg.value(metadata i32 %len, metadata !20, metadata !DIExpression()), !dbg !DILocation(scope: !16)
@@ -47,7 +74,6 @@
 ; CHECK: attributes #0 = { nounwind ssp }
 ; CHECK: attributes #1 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
 ; CHECK: attributes #2 = { noinline nounwind ssp }
-; CHECK: attributes [[NUW]] = { nounwind }
 
 !llvm.dbg.cu = !{!3}
 !llvm.module.flags = !{!30}
@@ -68,9 +94,7 @@
 !14 = distinct !DILexicalBlock(line: 12, column: 0, file: !28, scope: !1)
 !15 = !DILocalVariable(name: "name", line: 17, arg: 1, scope: !16, file: !2, type: !6)
 ; CHECK: !DISubprogram(name: "add_name_internal"
-; CHECK-SAME: type: ![[MD:[0-9]+]]
 !16 = distinct !DISubprogram(name: "add_name_internal", linkageName: "add_name_internal", line: 22, isLocal: true, isDefinition: true, virtualIndex: 6, isOptimized: false, unit: !3, file: !28, scope: !2, type: !17)
-; CHECK: ![[MD]] = !DISubroutineType(cc: DW_CC_nocall, types: !{{[0-9]+}})
 !17 = !DISubroutineType(types: !18)
 !18 = !{!6, !6, !9, !9, !19, !9}
 !19 = !DIBasicType(tag: DW_TAG_base_type, name: "unsigned char", size: 8, align: 8, encoding: DW_ATE_unsigned_char)
diff --git a/llvm/test/Transforms/DeadArgElim/musttail-indirect.ll b/llvm/test/Transforms/DeadArgElim/musttail-indirect.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/DeadArgElim/musttail-indirect.ll
@@ -0,0 +1,44 @@
+; This will fail if we don't produce correct IR.
+; RUN: opt -passes=deadargelim,verify -S < %s | FileCheck %s
+define internal i32 @test_caller(ptr %fptr, i32 %a, i32 %b) {
+  %r = musttail call i32 @test(ptr %fptr, i32 %a, i32 %b)
+  ret i32 %r
+}
+
+define internal i32 @test(ptr %fptr, i32 %a, i32 %b) {
+  %r = musttail call i32 %fptr(ptr %fptr, i32 %a, i32 0)
+  ret i32 %r
+}
+
+define internal i32 @direct_test() {
+  %r = musttail call i32 @foo()
+  ret i32 %r
+}
+
+declare i32 @foo()
+
+define internal i32 @ping(i32 %x) {
+  %r = musttail call i32 @pong(i32 %x)
+  ret i32 %r
+}
+
+define internal i32 @pong(i32 %x) {
+  %cond = icmp eq i32 %x, 2
+  br i1 %cond, label %yes, label %no
+
+yes:
+  %r1 = musttail call i32 @ping(i32 %x)
+  ret i32 %r1
+no:
+  %r2 = musttail call i32 @bar(i32 %x)
+  ret i32 %r2
+}
+
+declare i32 @bar(i32 %x)
+
+; CHECK: define internal i32 @test_caller
+; CHECK-NEXT: %r = musttail call i32 @test
+
+; CHECK: define internal i32 @test
+; CHECK-NEXT: %r = musttail call i32 %fptr
+