Index: clang/include/clang/Basic/IdentifierTable.h
===================================================================
--- clang/include/clang/Basic/IdentifierTable.h
+++ clang/include/clang/Basic/IdentifierTable.h
@@ -384,6 +384,17 @@
     return getName().startswith("<#") && getName().endswith("#>");
   }
 
+  /// Determine whether \p this is a name reserved for the implementation (C99
+  /// 7.1.3, C++ [lib.global.names]).
+  bool isReservedName(bool doubleUnderscoreOnly = false) const {
+    if (getLength() < 2)
+      return false;
+    const char *Name = getNameStart();
+    return Name[0] == '_' &&
+           (Name[1] == '_' ||
+            (Name[1] >= 'A' && Name[1] <= 'Z' && !doubleUnderscoreOnly));
+  }
+
   /// Provide less than operator for lexicographical sorting.
   bool operator<(const IdentifierInfo &RHS) const {
     return getName() < RHS.getName();
Index: clang/lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- clang/lib/CodeGen/CGDebugInfo.cpp
+++ clang/lib/CodeGen/CGDebugInfo.cpp
@@ -3748,21 +3748,29 @@
 void CGDebugInfo::EmitFuncDeclForCallSite(llvm::CallBase *CallOrInvoke,
                                           QualType CalleeType,
                                           const FunctionDecl *CalleeDecl) {
-  auto &CGOpts = CGM.getCodeGenOpts();
-  if (!CGOpts.EnableDebugEntryValues || !CGM.getLangOpts().Optimize ||
-      !CallOrInvoke)
+  if (!CallOrInvoke)
     return;
-
   auto *Func = CallOrInvoke->getCalledFunction();
   if (!Func)
     return;
+  if (Func->getSubprogram())
+    return;
+
+  // Do not emit a declaration subprogram for a builtin or if call site info
+  // isn't required. Also, elide declarations for functions with reserved names,
+  // as call site-related features aren't interesting in this case (& also, the
+  // compiler may emit calls to these functions without debug locations, which
+  // makes the verifier complain).
+  if (CalleeDecl->getBuiltinID() != 0 ||
+      getCallSiteRelatedAttrs() == llvm::DINode::FlagZero)
+    return;
+  if (const auto *Id = CalleeDecl->getIdentifier())
+    if (Id->isReservedName())
+      return;
 
   // If there is no DISubprogram attached to the function being called,
   // create the one describing the function in order to have complete
   // call site debug info.
-  if (Func->getSubprogram())
-    return;
-
   if (!CalleeDecl->isStatic() && !CalleeDecl->isInlined())
     EmitFunctionDecl(CalleeDecl, CalleeDecl->getLocation(), CalleeType, Func);
 }
@@ -4824,10 +4832,10 @@
   bool SupportsDWARFv4Ext =
       CGM.getCodeGenOpts().DwarfVersion == 4 &&
       (CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::LLDB ||
-       (CGM.getCodeGenOpts().EnableDebugEntryValues &&
-       CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::GDB));
+       CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::GDB);
 
-  if (!SupportsDWARFv4Ext && CGM.getCodeGenOpts().DwarfVersion < 5)
+  if (!SupportsDWARFv4Ext && CGM.getCodeGenOpts().DwarfVersion < 5 &&
+      !CGM.getCodeGenOpts().EnableDebugEntryValues)
     return llvm::DINode::FlagZero;
 
   return llvm::DINode::FlagAllCallsDescribed;
Index: clang/lib/Sema/SemaCodeComplete.cpp
===================================================================
--- clang/lib/Sema/SemaCodeComplete.cpp
+++ clang/lib/Sema/SemaCodeComplete.cpp
@@ -692,18 +692,6 @@
   return Result;
 }
 
-/// Determine whether \p Id is a name reserved for the implementation (C99
-/// 7.1.3, C++ [lib.global.names]).
-static bool isReservedName(const IdentifierInfo *Id,
-                           bool doubleUnderscoreOnly = false) {
-  if (Id->getLength() < 2)
-    return false;
-  const char *Name = Id->getNameStart();
-  return Name[0] == '_' &&
-         (Name[1] == '_' ||
-          (Name[1] >= 'A' && Name[1] <= 'Z' && !doubleUnderscoreOnly));
-}
-
 // Some declarations have reserved names that we don't want to ever show.
 // Filter out names reserved for the implementation if they come from a
 // system header.
@@ -713,13 +701,13 @@
     return false;
 
   // Ignore reserved names for compiler provided decls.
-  if (isReservedName(Id) && ND->getLocation().isInvalid())
+  if (Id->isReservedName() && ND->getLocation().isInvalid())
     return true;
 
   // For system headers ignore only double-underscore names.
   // This allows for system headers providing private symbols with a single
   // underscore.
-  if (isReservedName(Id, /*doubleUnderscoreOnly=*/true) &&
+  if (Id->isReservedName(/*doubleUnderscoreOnly=*/true) &&
       SemaRef.SourceMgr.isInSystemHeader(
           SemaRef.SourceMgr.getSpellingLoc(ND->getLocation())))
     return true;
Index: clang/test/CodeGen/debug-info-extern-call.c
===================================================================
--- clang/test/CodeGen/debug-info-extern-call.c
+++ clang/test/CodeGen/debug-info-extern-call.c
@@ -1,15 +1,39 @@
-// RUN: %clang -Xclang -femit-debug-entry-values -g -O2 -target x86_64-none-linux-gnu -S -emit-llvm %s -o - | FileCheck %s -check-prefix=CHECK-EXT
-// CHECK-EXT: !DISubprogram(name: "fn1"
+// When entry values are emitted, expect a subprogram for extern decls so that
+// the dwarf generator can describe call site parameters at extern call sites.
+//
+// RUN: %clang -Xclang -femit-debug-entry-values -g -O2 -target x86_64-none-linux-gnu -S -emit-llvm %s -o - \
+// RUN:   | FileCheck %s -check-prefix=DECLS-FOR-EXTERN
 
-// RUN: %clang -g -O2 -target x86_64-none-linux-gnu -S -emit-llvm %s -o - | FileCheck %s
-// CHECK-NOT: !DISubprogram(name: "fn1"
+// Similarly, when the debugger tuning is gdb, expect a subprogram for extern
+// decls so that the dwarf generator can describe information needed for tail
+// call frame reconstrution.
+//
+// RUN: %clang -g -O2 -target x86_64-none-linux-gnu -ggdb -S -emit-llvm %s -o - \
+// RUN:   | FileCheck %s -check-prefix=DECLS-FOR-EXTERN
+//
+// Do not emit a subprogram for extern decls when entry values are disabled and
+// the tuning is not set to gdb.
+//
+// RUN: %clang -g -O2 -target x86_64-none-linux-gnu -gsce -S -emit-llvm %s -o - \
+// RUN:   | FileCheck %s -check-prefix=NO-DECLS-FOR-EXTERN
+
+// DECLS-FOR-EXTERN: !DISubprogram(name: "fn1"
+// DECLS-FOR-EXTERN-NOT: !DISubprogram(name: "memcmp"
+// DECLS-FOR-EXTERN-NOT: !DISubprogram(name: "__some_reserved_name"
+
+// NO-DECLS-FOR-EXTERN-NOT: !DISubprogram(name: "fn1"
+// NO-DECLS-FOR-EXTERN-NOT: !DISubprogram(name: "memcmp"
+// NO-DECLS-FOR-EXTERN-NOT: !DISubprogram(name: "__some_reserved_name"
 
 extern int fn1(int a, int b);
+extern int memcmp(const void *s1, const void *s2, unsigned long n);
+extern void __some_reserved_name(void);
 
-int fn2 () {
+int fn2 (int *src, int *dst) {
   int x = 4, y = 5;
   int res = fn1(x, y);
-
-  return res;
+  int res2 = memcmp(dst, src, res);
+  __some_reserved_name();
+  return res + res2;
 }
 
Index: clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp
===================================================================
--- clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp
+++ clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp
@@ -56,6 +56,7 @@
 
 // NO-ATTR-NOT: FlagAllCallsDescribed
 
+// HAS-ATTR-DAG: DISubprogram(name: "declaration1", {{.*}}, flags: DIFlagPrototyped
 // HAS-ATTR-DAG: DISubprogram(name: "declaration2", {{.*}}, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition
 // HAS-ATTR-DAG: DISubprogram(name: "struct1", {{.*}}, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized)
 // HAS-ATTR-DAG: DISubprogram(name: "struct1", {{.*}}, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition
Index: llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll
===================================================================
--- llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll
+++ llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll
@@ -25,6 +25,14 @@
 
 @sink = global i32 0, align 4, !dbg !0
 
+define void @__has_no_subprogram() {
+entry:
+  %0 = load volatile i32, i32* @sink, align 4
+  %inc = add nsw i32 %0, 1
+  store volatile i32 %inc, i32* @sink, align 4
+  ret void
+}
+
 ; ASM: DW_TAG_subprogram
 ; ASM:   DW_AT_call_all_calls
 ; OBJ: [[bat_sp:.*]]: DW_TAG_subprogram
@@ -70,6 +78,7 @@
 ; OBJ:     DW_AT_call_tail_call
 define void @_Z3foov() !dbg !25 {
 entry:
+  tail call void @__has_no_subprogram()
   tail call void @_Z3barv(), !dbg !26
   tail call void @_Z3batv(), !dbg !27
   tail call void @_Z3barv(), !dbg !26