Index: docs/LangRef.rst
===================================================================
--- docs/LangRef.rst
+++ docs/LangRef.rst
@@ -4742,6 +4742,15 @@
 this property for each DILocalVariable. The flag should be used
 only in optimized code.
 
+DISPFlags
+"""""""""""""""
+
+These flags encode various properties of DISubprograms.
+
+The `DeclForCallSite` flag marks a function declaration subprogram created for
+call site debug information. The subprogram gets created if a called function
+does not have a subprogram attached, which is specific to external functions.
+
 DIObjCProperty
 """"""""""""""
 
Index: include/llvm/IR/DIBuilder.h
===================================================================
--- include/llvm/IR/DIBuilder.h
+++ include/llvm/IR/DIBuilder.h
@@ -665,7 +665,8 @@
                    DISubprogram::DISPFlags SPFlags = DISubprogram::SPFlagZero,
                    DITemplateParameterArray TParams = nullptr,
                    DISubprogram *Decl = nullptr,
-                   DITypeArray ThrownTypes = nullptr);
+                   DITypeArray ThrownTypes = nullptr,
+                   bool isDeclForCallSite = false);
 
     /// Identical to createFunction,
     /// except that the resulting DbgNode is meant to be RAUWed.
Index: include/llvm/IR/DebugInfoFlags.def
===================================================================
--- include/llvm/IR/DebugInfoFlags.def
+++ include/llvm/IR/DebugInfoFlags.def
@@ -88,11 +88,12 @@
 HANDLE_DISP_FLAG((1u << 6), Elemental)
 HANDLE_DISP_FLAG((1u << 7), Recursive)
 HANDLE_DISP_FLAG((1u << 8), MainSubprogram)
+HANDLE_DISP_FLAG((1u << 9), DeclForCallSite)
 
 #ifdef DISP_FLAG_LARGEST_NEEDED
 // Intended to be used with ADT/BitmaskEnum.h.
 // NOTE: Always must be equal to largest flag, check this when adding new flags.
-HANDLE_DISP_FLAG((1 << 8), Largest)
+HANDLE_DISP_FLAG((1 << 9), Largest)
 #undef DISP_FLAG_LARGEST_NEEDED
 #endif
 
Index: include/llvm/IR/DebugInfoMetadata.h
===================================================================
--- include/llvm/IR/DebugInfoMetadata.h
+++ include/llvm/IR/DebugInfoMetadata.h
@@ -1739,6 +1739,7 @@
   bool isDefinition() const { return getSPFlags() & SPFlagDefinition; }
   bool isOptimized() const { return getSPFlags() & SPFlagOptimized; }
   bool isMainSubprogram() const { return getSPFlags() & SPFlagMainSubprogram; }
+  bool isDeclForCallSite() const { return getSPFlags() & SPFlagDeclForCallSite; }
 
   bool isArtificial() const { return getFlags() & FlagArtificial; }
   bool isPrivate() const {
Index: lib/CodeGen/AsmPrinter/DwarfDebug.cpp
===================================================================
--- lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -669,6 +669,11 @@
     NewCU.setSection(Asm->getObjFileLowering().getDwarfInfoSection());
   }
 
+  // Create DIEs for function declaraions used for dbg call sites.
+  for (auto Scope : DIUnit->getRetainedTypes())
+    if (auto *SP = dyn_cast_or_null<DISubprogram>(Scope))
+      NewCU.getOrCreateSubprogramDIE(SP);
+
   CUMap.insert({DIUnit, &NewCU});
   CUDieMap.insert({&NewCU.getUnitDie(), &NewCU});
   return NewCU;
Index: lib/IR/DIBuilder.cpp
===================================================================
--- lib/IR/DIBuilder.cpp
+++ lib/IR/DIBuilder.cpp
@@ -753,7 +753,7 @@
     unsigned LineNo, DISubroutineType *Ty, unsigned ScopeLine,
     DINode::DIFlags Flags, DISubprogram::DISPFlags SPFlags,
     DITemplateParameterArray TParams, DISubprogram *Decl,
-    DITypeArray ThrownTypes) {
+    DITypeArray ThrownTypes, bool isDeclForCallSite) {
   bool IsDefinition = SPFlags & DISubprogram::SPFlagDefinition;
   auto *Node = getSubprogram(
       /*IsDistinct=*/IsDefinition, VMContext, getNonCompileUnitScope(Context),
@@ -761,7 +761,7 @@
       SPFlags, IsDefinition ? CUNode : nullptr, TParams, Decl,
       MDTuple::getTemporary(VMContext, None).release(), ThrownTypes);
 
-  if (IsDefinition)
+  if (IsDefinition || isDeclForCallSite)
     AllSubprograms.push_back(Node);
   trackIfUnresolved(Node);
   return Node;
Index: lib/IR/Verifier.cpp
===================================================================
--- lib/IR/Verifier.cpp
+++ lib/IR/Verifier.cpp
@@ -2223,8 +2223,10 @@
            MDs.empty() ? nullptr : MDs.front().second);
   } else if (F.isDeclaration()) {
     for (const auto &I : MDs) {
-      AssertDI(I.first != LLVMContext::MD_dbg,
-               "function declaration may not have a !dbg attachment", &F);
+      AssertDI(I.first != LLVMContext::MD_dbg ||
+               cast<DISubprogram>(I.second)->isDeclForCallSite(),
+               "function declaration may not have a !dbg attachment, "
+               "except function declarations for call site debug info", &F);
       Assert(I.first != LLVMContext::MD_prof,
              "function declaration may not have a !prof attachment", &F);
 
Index: test/Verifier/metadata-function-dbg.ll
===================================================================
--- test/Verifier/metadata-function-dbg.ll
+++ test/Verifier/metadata-function-dbg.ll
@@ -3,6 +3,9 @@
 ; CHECK:      function declaration may not have a !dbg attachment
 declare !dbg !4 void @f1()
 
+; CHECK-NOT:  function declaration may not have a !dbg attachment
+declare !dbg !5 void @f5()
+
 ; CHECK:      function must have a single !dbg attachment
 define void @f2() !dbg !4 !dbg !4 {
   unreachable
@@ -35,3 +38,4 @@
 !2 = !DIFile(filename: "t.c", directory: "/path/to/dir")
 !3 = !{}
 !4 = distinct !DISubprogram(name: "foo", scope: !1, file: !2, unit: !1)
+!5 = distinct !DISubprogram(name: "f5", scope: !1, file: !2, unit: !1, spFlags: DISPFlagDeclForCallSite)