Index: llvm/include/llvm/CodeGen/MachineFunction.h
===================================================================
--- llvm/include/llvm/CodeGen/MachineFunction.h
+++ llvm/include/llvm/CodeGen/MachineFunction.h
@@ -536,6 +536,10 @@
   /// (or DBG_PHI).
   void finalizeDebugInstrRefs();
 
+  /// Returns true if functions variable locations should be tracked with
+  /// instruction referencing.
+  bool useDebugInstrRef() const;
+
   MachineFunction(Function &F, const LLVMTargetMachine &Target,
                   const TargetSubtargetInfo &STI, unsigned FunctionNum,
                   MachineModuleInfo &MMI);
Index: llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
===================================================================
--- llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
+++ llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp
@@ -99,12 +99,7 @@
 bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
   if (!TheImpl) {
     TPC = getAnalysisIfAvailable<TargetPassConfig>();
-
-    bool InstrRefBased = false;
-    if (TPC) {
-      auto &TM = TPC->getTM<TargetMachine>();
-      InstrRefBased = TM.Options.ValueTrackingVariableLocations;
-    }
+    bool InstrRefBased = MF.useDebugInstrRef();
 
     // Allow the user to force selection of InstrRef LDV.
     InstrRefBased |= ForceInstrRefLDV;
Index: llvm/lib/CodeGen/LiveDebugVariables.cpp
===================================================================
--- llvm/lib/CodeGen/LiveDebugVariables.cpp
+++ llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -1314,12 +1314,7 @@
 
   // Have we been asked to track variable locations using instruction
   // referencing?
-  bool InstrRef = false;
-  auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
-  if (TPC) {
-    auto &TM = TPC->getTM<TargetMachine>();
-    InstrRef = TM.Options.ValueTrackingVariableLocations;
-  }
+  bool InstrRef = mf.useDebugInstrRef();
 
   if (!pImpl)
     pImpl = new LDVImpl(this);
Index: llvm/lib/CodeGen/MachineFunction.cpp
===================================================================
--- llvm/lib/CodeGen/MachineFunction.cpp
+++ llvm/lib/CodeGen/MachineFunction.cpp
@@ -1174,7 +1174,7 @@
     MI.getOperand(0).setIsDebug();
   };
 
-  if (!getTarget().Options.ValueTrackingVariableLocations)
+  if (!useDebugInstrRef())
     return;
 
   for (auto &MBB : *this) {
@@ -1221,6 +1221,20 @@
   }
 }
 
+bool MachineFunction::useDebugInstrRef() const {
+  // Disable instr-ref at -O0: it's very slow (in compile time). We can still
+  // have optimized code inlined into this unoptimized code, however with
+  // fewer and less aggressive optimizations happening, coverage and accuracy
+  // should not suffer.
+  if (getTarget().getOptLevel() == CodeGenOpt::None)
+    return false;
+
+  if (getTarget().Options.ValueTrackingVariableLocations)
+    return true;
+
+  return false;
+}
+
 /// \}
 
 //===----------------------------------------------------------------------===//
Index: llvm/test/DebugInfo/X86/instr-ref-opt-levels.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/X86/instr-ref-opt-levels.ll
@@ -0,0 +1,42 @@
+; RUN: llc -mtriple=x86_64-- %s -o - -O0 -stop-before=finalize-isel \
+; RUN:    | FileCheck %s --check-prefix=O0 --implicit-check-not=DBG_INSTR_REF
+; RUN: llc -mtriple=x86_64-- %s -o - -O2 -stop-before=finalize-isel \
+; RUN:    | FileCheck %s --check-prefix=O2 --implicit-check-not=DBG_VALUE
+; Test that instruction-referencing variable locations are issued at -O2, but
+; normal DBG_VALUEs are issued at -O0. This behaviour is desired as the former
+; is slow when applied to unoptimized code.
+; (Copy + pasted from ./dead-store-elimination-marks-undef.ll),
+
+; O0: DBG_VALUE
+; O2: DBG_VALUE
+
+@b = common dso_local local_unnamed_addr global i32 0, align 1
+
+define dso_local i32 @main() local_unnamed_addr !dbg !7 {
+  %1 = alloca i32, align 4
+  %2 = load i32, i32* @b, align 1, !dbg !13
+  call void @llvm.dbg.value(metadata i32 %2, metadata !12, metadata !DIExpression()), !dbg !13
+  store i32 %2, i32* %1, align 4, !dbg !13
+  ret i32 0, !dbg !13
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !2, nameTableKind: None)
+!1 = !DIFile(filename: "dead-store-elimination-marks-undef.ll", directory: "/temp/bz45080")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = !{!"clang version 10.0.0"}
+!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 3, type: !8, scopeLine: 3, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "l_2864", scope: !7, file: !1, line: 4, type: !10)
+!13 = !DILocation(line: 5, column: 12, scope: !7)
+