Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -5180,10 +5180,6 @@
   CodeGenOpts<"DebugPassManager">, DefaultFalse,
   PosFlag<SetTrue, [], "Prints debug information for the new pass manager">,
   NegFlag<SetFalse, [], "Disables debug printing for the new pass manager">>;
-def fexperimental_debug_variable_locations : Flag<["-"],
-    "fexperimental-debug-variable-locations">,
-    HelpText<"Use experimental new value-tracking variable locations">,
-    MarshallingInfoFlag<CodeGenOpts<"ValueTrackingVariableLocations">>;
 def fverify_debuginfo_preserve
     : Flag<["-"], "fverify-debuginfo-preserve">,
       HelpText<"Enable Debug Info Metadata preservation testing in "
Index: llvm/include/llvm/CodeGen/CommandFlags.h
===================================================================
--- llvm/include/llvm/CodeGen/CommandFlags.h
+++ llvm/include/llvm/CodeGen/CommandFlags.h
@@ -130,6 +130,7 @@
 bool getEnableDebugEntryValues();
 
 bool getValueTrackingVariableLocations();
+Optional<bool> getExplicitValueTrackingVariableLocations();
 
 bool getForceDwarfFrameSection();
 
@@ -170,6 +171,10 @@
 /// Set function attributes of functions in Module M based on CPU,
 /// Features, and command line flags.
 void setFunctionAttributes(StringRef CPU, StringRef Features, Module &M);
+
+/// Should value-tracking variable locations / instruction referencing be
+/// enabled by default for this triple?
+bool getDefaultValueTrackingVariableLocations(const llvm::Triple &T);
 } // namespace codegen
 } // namespace llvm
 
Index: llvm/lib/CodeGen/CommandFlags.cpp
===================================================================
--- llvm/lib/CodeGen/CommandFlags.cpp
+++ llvm/lib/CodeGen/CommandFlags.cpp
@@ -90,7 +90,7 @@
 CGOPT(bool, EmitCallSiteInfo)
 CGOPT(bool, EnableMachineFunctionSplitter)
 CGOPT(bool, EnableDebugEntryValues)
-CGOPT(bool, ValueTrackingVariableLocations)
+CGOPT_EXP(bool, ValueTrackingVariableLocations)
 CGOPT(bool, ForceDwarfFrameSection)
 CGOPT(bool, XRayOmitFunctionIndex)
 CGOPT(bool, DebugStrictDwarf)
@@ -534,12 +534,17 @@
   Options.EmitAddrsig = getEnableAddrsig();
   Options.EmitCallSiteInfo = getEmitCallSiteInfo();
   Options.EnableDebugEntryValues = getEnableDebugEntryValues();
-  Options.ValueTrackingVariableLocations = getValueTrackingVariableLocations();
   Options.ForceDwarfFrameSection = getForceDwarfFrameSection();
   Options.XRayOmitFunctionIndex = getXRayOmitFunctionIndex();
   Options.DebugStrictDwarf = getDebugStrictDwarf();
   Options.LoopAlignment = getAlignLoops();
 
+  if (auto Opt = getExplicitValueTrackingVariableLocations())
+    Options.ValueTrackingVariableLocations = *Opt;
+  else
+    Options.ValueTrackingVariableLocations =
+        getDefaultValueTrackingVariableLocations(TheTriple);
+
   Options.MCOptions = mc::InitMCTargetOptionsFromFlags();
 
   Options.ThreadModel = getThreadModel();
@@ -692,3 +697,9 @@
   for (Function &F : M)
     setFunctionAttributes(CPU, Features, F);
 }
+
+bool codegen::getDefaultValueTrackingVariableLocations(const llvm::Triple &T) {
+  if (T.getArch() == llvm::Triple::x86_64)
+    return true;
+  return false;
+}
Index: llvm/lib/Target/X86/X86TargetMachine.cpp
===================================================================
--- llvm/lib/Target/X86/X86TargetMachine.cpp
+++ llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -26,6 +26,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/CodeGen/CommandFlags.h"
 #include "llvm/CodeGen/ExecutionDomainFix.h"
 #include "llvm/CodeGen/GlobalISel/CallLowering.h"
 #include "llvm/CodeGen/GlobalISel/IRTranslator.h"
Index: llvm/test/DebugInfo/X86/instr-ref-flag.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/X86/instr-ref-flag.ll
@@ -0,0 +1,46 @@
+; RUN: llc %s -o - -stop-before=finalize-isel -march=x86-64 \
+; RUN: | FileCheck %s --check-prefixes=INSTRREFON
+; RUN: llc %s -o - -stop-before=finalize-isel -march=x86-64 \
+; RUN:    -experimental-debug-variable-locations=true \
+; RUN: | FileCheck %s --check-prefixes=INSTRREFON
+
+; RUN: llc %s -o - -stop-before=finalize-isel -march=x86-64 \
+; RUN:    -experimental-debug-variable-locations=false \
+; RUN: | FileCheck %s --check-prefixes=INSTRREFOFF \
+; RUN:    --implicit-check-not=DBG_INSTR_REF
+
+;; This test checks that for an x86 triple, instruction referencing is used
+;; by llc by default, and that it can be turned explicitly on or off as
+;; desired.
+
+; INSTRREFON: DBG_INSTR_REF
+; INSTRREFOFF: DBG_VALUE
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-unknown"
+
+define hidden i32 @foo(i32 %a) local_unnamed_addr !dbg !7 {
+  %b = add i32 %a, 1
+  call void @llvm.dbg.value(metadata i32 %b, metadata !11, metadata !DIExpression()), !dbg !12
+  ret i32 %b, !dbg !12
+}
+
+; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "foo.cpp", directory: ".")
+!2 = !DIBasicType(name: "int", size: 8, encoding: DW_ATE_signed)
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 2}
+!6 = !{i32 7, !"PIC Level", i32 2}
+!7 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: !1, file: !1, line: 6, type: !8, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !10)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!2, !2}
+!10 = !{!11}
+!11 = !DILocalVariable(name: "baz", scope: !7, file: !1, line: 7, type: !2)
+!12 = !DILocation(line: 10, scope: !7)