Index: bolt/include/bolt/Core/BinaryContext.h
===================================================================
--- bolt/include/bolt/Core/BinaryContext.h
+++ bolt/include/bolt/Core/BinaryContext.h
@@ -37,12 +37,12 @@
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/RWMutex.h"
 #include "llvm/Support/raw_ostream.h"
 #include <functional>
 #include <list>
 #include <map>
 #include <set>
-#include <shared_mutex>
 #include <string>
 #include <system_error>
 #include <type_traits>
@@ -190,7 +190,7 @@
   std::map<uint64_t, BinaryFunction> BinaryFunctions;
 
   /// A mutex that is used to control parallel accesses to BinaryFunctions
-  mutable std::shared_timed_mutex BinaryFunctionsMutex;
+  mutable llvm::sys::RWMutex BinaryFunctionsMutex;
 
   /// Functions injected by BOLT
   std::vector<BinaryFunction *> InjectedBinaryFunctions;
@@ -420,7 +420,7 @@
   std::unordered_map<const MCSymbol *, BinaryFunction *> SymbolToFunctionMap;
 
   /// A mutex that is used to control parallel accesses to SymbolToFunctionMap
-  mutable std::shared_timed_mutex SymbolToFunctionMapMutex;
+  mutable llvm::sys::RWMutex SymbolToFunctionMapMutex;
 
   /// Look up the symbol entry that contains the given \p Address (based on
   /// the start address and size for each symbol).  Returns a pointer to
@@ -556,9 +556,9 @@
   std::unique_ptr<MCContext> Ctx;
 
   /// A mutex that is used to control parallel accesses to Ctx
-  mutable std::shared_timed_mutex CtxMutex;
-  std::unique_lock<std::shared_timed_mutex> scopeLock() const {
-    return std::unique_lock<std::shared_timed_mutex>(CtxMutex);
+  mutable llvm::sys::RWMutex CtxMutex;
+  std::unique_lock<llvm::sys::RWMutex> scopeLock() const {
+    return std::unique_lock<llvm::sys::RWMutex>(CtxMutex);
   }
 
   std::unique_ptr<DWARFContext> DwCtx;
Index: bolt/include/bolt/Core/BinaryFunction.h
===================================================================
--- bolt/include/bolt/Core/BinaryFunction.h
+++ bolt/include/bolt/Core/BinaryFunction.h
@@ -45,6 +45,7 @@
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Object/ObjectFile.h"
+#include "llvm/Support/RWMutex.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <iterator>
@@ -1166,7 +1167,7 @@
 
     MCSymbol *&FunctionEndLabel = FunctionEndLabels[LabelIndex];
     if (!FunctionEndLabel) {
-      std::unique_lock<std::shared_timed_mutex> Lock(BC.CtxMutex);
+      std::unique_lock<llvm::sys::RWMutex> Lock(BC.CtxMutex);
       if (Fragment == FragmentNum::main())
         FunctionEndLabel = BC.Ctx->createNamedTempSymbol("func_end");
       else
@@ -1490,7 +1491,7 @@
   std::unique_ptr<BinaryBasicBlock>
   createBasicBlock(MCSymbol *Label = nullptr) {
     if (!Label) {
-      std::unique_lock<std::shared_timed_mutex> Lock(BC.CtxMutex);
+      std::unique_lock<llvm::sys::RWMutex> Lock(BC.CtxMutex);
       Label = BC.Ctx->createNamedTempSymbol("BB");
     }
     auto BB =
Index: bolt/include/bolt/Passes/Aligner.h
===================================================================
--- bolt/include/bolt/Passes/Aligner.h
+++ bolt/include/bolt/Passes/Aligner.h
@@ -16,6 +16,7 @@
 #define BOLT_PASSES_ALIGNER_H
 
 #include "bolt/Passes/BinaryPasses.h"
+#include "llvm/Support/RWMutex.h"
 
 namespace llvm {
 namespace bolt {
@@ -24,7 +25,7 @@
 private:
   /// Stats for usage of max bytes for basic block alignment.
   std::vector<uint32_t> AlignHistogram;
-  std::shared_timed_mutex AlignHistogramMtx;
+  llvm::sys::RWMutex AlignHistogramMtx;
 
   /// Stats: execution count of blocks that were aligned.
   std::atomic<uint64_t> AlignedBlocksCount{0};
Index: bolt/include/bolt/Passes/Instrumentation.h
===================================================================
--- bolt/include/bolt/Passes/Instrumentation.h
+++ bolt/include/bolt/Passes/Instrumentation.h
@@ -19,6 +19,7 @@
 
 #include "bolt/Passes/BinaryPasses.h"
 #include "bolt/Passes/InstrumentationSummary.h"
+#include "llvm/Support/RWMutex.h"
 
 namespace llvm {
 namespace bolt {
@@ -109,7 +110,7 @@
   /// strtab indices in StringTable for each function name
   std::unordered_map<const BinaryFunction *, uint32_t> FuncToStringIdx;
 
-  mutable std::shared_timed_mutex FDMutex;
+  mutable llvm::sys::RWMutex FDMutex;
 
   /// The data generated during Instrumentation pass that needs to
   /// be passed to the Instrument runtime library.
Index: bolt/lib/Core/BinaryBasicBlock.cpp
===================================================================
--- bolt/lib/Core/BinaryBasicBlock.cpp
+++ bolt/lib/Core/BinaryBasicBlock.cpp
@@ -491,7 +491,7 @@
   assert(isSuccessor(Successor));
   BinaryContext &BC = Function->getBinaryContext();
   MCInst NewInst;
-  std::unique_lock<std::shared_timed_mutex> Lock(BC.CtxMutex);
+  std::unique_lock<llvm::sys::RWMutex> Lock(BC.CtxMutex);
   BC.MIB->createUncondBranch(NewInst, Successor->getLabel(), BC.Ctx.get());
   Instructions.emplace_back(std::move(NewInst));
 }
Index: bolt/lib/Core/BinaryContext.cpp
===================================================================
--- bolt/lib/Core/BinaryContext.cpp
+++ bolt/lib/Core/BinaryContext.cpp
@@ -1316,9 +1316,8 @@
   assert(!ChildBF.isMultiEntry() && !ParentBF.isMultiEntry() &&
          "cannot merge functions with multiple entry points");
 
-  std::unique_lock<std::shared_timed_mutex> WriteCtxLock(CtxMutex,
-                                                         std::defer_lock);
-  std::unique_lock<std::shared_timed_mutex> WriteSymbolMapLock(
+  std::unique_lock<llvm::sys::RWMutex> WriteCtxLock(CtxMutex, std::defer_lock);
+  std::unique_lock<llvm::sys::RWMutex> WriteSymbolMapLock(
       SymbolToFunctionMapMutex, std::defer_lock);
 
   const StringRef ChildName = ChildBF.getOneName();
@@ -1343,10 +1342,10 @@
     // continue to exist and either one can be executed.
     ChildBF.mergeProfileDataInto(ParentBF);
 
-    std::shared_lock<std::shared_timed_mutex> ReadBfsLock(BinaryFunctionsMutex,
-                                                          std::defer_lock);
-    std::unique_lock<std::shared_timed_mutex> WriteBfsLock(BinaryFunctionsMutex,
-                                                           std::defer_lock);
+    std::shared_lock<llvm::sys::RWMutex> ReadBfsLock(BinaryFunctionsMutex,
+                                                     std::defer_lock);
+    std::unique_lock<llvm::sys::RWMutex> WriteBfsLock(BinaryFunctionsMutex,
+                                                      std::defer_lock);
     // Remove ChildBF from the global set of functions in relocs mode.
     ReadBfsLock.lock();
     auto FI = BinaryFunctions.find(ChildBF.getAddress());
@@ -2157,7 +2156,7 @@
 
 BinaryFunction *BinaryContext::getFunctionForSymbol(const MCSymbol *Symbol,
                                                     uint64_t *EntryDesc) {
-  std::shared_lock<std::shared_timed_mutex> Lock(SymbolToFunctionMapMutex);
+  std::shared_lock<llvm::sys::RWMutex> Lock(SymbolToFunctionMapMutex);
   auto BFI = SymbolToFunctionMap.find(Symbol);
   if (BFI == SymbolToFunctionMap.end())
     return nullptr;
Index: bolt/lib/Core/Exceptions.cpp
===================================================================
--- bolt/lib/Core/Exceptions.cpp
+++ bolt/lib/Core/Exceptions.cpp
@@ -406,7 +406,7 @@
         const MCSymbol *EHSymbol;
         MCInst EHLabel;
         {
-          std::unique_lock<std::shared_timed_mutex> Lock(BC.CtxMutex);
+          std::unique_lock<llvm::sys::RWMutex> Lock(BC.CtxMutex);
           EHSymbol = BC.Ctx->createNamedTempSymbol("EH");
           BC.MIB->createEHLabel(EHLabel, EHSymbol, BC.Ctx.get());
         }
Index: bolt/lib/Core/ParallelUtilities.cpp
===================================================================
--- bolt/lib/Core/ParallelUtilities.cpp
+++ bolt/lib/Core/ParallelUtilities.cpp
@@ -13,10 +13,10 @@
 #include "bolt/Core/ParallelUtilities.h"
 #include "bolt/Core/BinaryContext.h"
 #include "bolt/Core/BinaryFunction.h"
+#include "llvm/Support/RWMutex.h"
 #include "llvm/Support/ThreadPool.h"
 #include "llvm/Support/Timer.h"
 #include <mutex>
-#include <shared_mutex>
 
 #define DEBUG_TYPE "par-utils"
 
@@ -170,13 +170,13 @@
   if (BC.getBinaryFunctions().size() == 0)
     return;
 
-  std::shared_timed_mutex MainLock;
+  llvm::sys::RWMutex MainLock;
   auto runBlock = [&](std::map<uint64_t, BinaryFunction>::iterator BlockBegin,
                       std::map<uint64_t, BinaryFunction>::iterator BlockEnd,
                       MCPlusBuilder::AllocatorIdTy AllocId) {
     Timer T(LogName, LogName);
     LLVM_DEBUG(T.startTimer());
-    std::shared_lock<std::shared_timed_mutex> Lock(MainLock);
+    std::shared_lock<llvm::sys::RWMutex> Lock(MainLock);
     for (auto It = BlockBegin; It != BlockEnd; ++It) {
       BinaryFunction &BF = It->second;
       if (SkipPredicate && SkipPredicate(BF))
@@ -192,7 +192,7 @@
     return;
   }
   // This lock is used to postpone task execution
-  std::unique_lock<std::shared_timed_mutex> Lock(MainLock);
+  std::unique_lock<llvm::sys::RWMutex> Lock(MainLock);
 
   // Estimate the overall runtime cost using the scheduling policy
   const unsigned TotalCost = estimateTotalCost(BC, SkipPredicate, SchedPolicy);
Index: bolt/lib/Passes/Aligner.cpp
===================================================================
--- bolt/lib/Passes/Aligner.cpp
+++ bolt/lib/Passes/Aligner.cpp
@@ -143,7 +143,7 @@
 
     // Update stats.
     LLVM_DEBUG(
-      std::unique_lock<std::shared_timed_mutex> Lock(AlignHistogramMtx);
+      std::unique_lock<llvm::sys::RWMutex> Lock(AlignHistogramMtx);
       AlignHistogram[BytesToUse]++;
       AlignedBlocksCount += BB->getKnownExecutionCount();
     );
Index: bolt/lib/Passes/Instrumentation.cpp
===================================================================
--- bolt/lib/Passes/Instrumentation.cpp
+++ bolt/lib/Passes/Instrumentation.cpp
@@ -15,6 +15,7 @@
 #include "bolt/RuntimeLibs/InstrumentationRuntimeLibrary.h"
 #include "bolt/Utils/Utils.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/RWMutex.h"
 #include <stack>
 
 #define DEBUG_TYPE "bolt-instrumentation"
@@ -298,7 +299,7 @@
 
   FunctionDescription *FuncDesc = nullptr;
   {
-    std::unique_lock<std::shared_timed_mutex> L(FDMutex);
+    std::unique_lock<llvm::sys::RWMutex> L(FDMutex);
     Summary->FunctionDescriptions.emplace_back();
     FuncDesc = &Summary->FunctionDescriptions.back();
   }