diff --git a/clang/include/clang/Driver/ToolChain.h b/clang/include/clang/Driver/ToolChain.h
--- a/clang/include/clang/Driver/ToolChain.h
+++ b/clang/include/clang/Driver/ToolChain.h
@@ -456,6 +456,12 @@
   /// by default.
   virtual bool IsUnwindTablesDefault(const llvm::opt::ArgList &Args) const;
 
+  /// Test whether this toolchain supports outline atomics by default.
+  virtual bool
+  IsAArch64OutlineAtomicsDefault(const llvm::opt::ArgList &Args) const {
+    return false;
+  }
+
   /// Test whether this toolchain defaults to PIC.
   virtual bool isPICDefault() const = 0;
 
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6441,6 +6441,12 @@
       CmdArgs.push_back("-target-feature");
       CmdArgs.push_back("-outline-atomics");
     }
+  } else {
+    if (Triple.isAArch64() &&
+        getToolChain().IsAArch64OutlineAtomicsDefault(Args)) {
+      CmdArgs.push_back("-target-feature");
+      CmdArgs.push_back("+outline-atomics");
+    }
   }
 
   if (Args.hasFlag(options::OPT_faddrsig, options::OPT_fno_addrsig,
diff --git a/clang/lib/Driver/ToolChains/Linux.h b/clang/lib/Driver/ToolChains/Linux.h
--- a/clang/lib/Driver/ToolChains/Linux.h
+++ b/clang/lib/Driver/ToolChains/Linux.h
@@ -36,6 +36,8 @@
   void AddIAMCUIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                            llvm::opt::ArgStringList &CC1Args) const override;
   CXXStdlibType GetDefaultCXXStdlibType() const override;
+  bool
+  IsAArch64OutlineAtomicsDefault(const llvm::opt::ArgList &Args) const override;
   bool isPIEDefault() const override;
   bool isNoExecStackDefault() const override;
   bool IsMathErrnoDefault() const override;
diff --git a/clang/lib/Driver/ToolChains/Linux.cpp b/clang/lib/Driver/ToolChains/Linux.cpp
--- a/clang/lib/Driver/ToolChains/Linux.cpp
+++ b/clang/lib/Driver/ToolChains/Linux.cpp
@@ -836,6 +836,21 @@
           getTriple().isMusl() || getSanitizerArgs().requiresPIE();
 }
 
+bool Linux::IsAArch64OutlineAtomicsDefault(const ArgList &Args) const {
+  if (!getTriple().isAArch64())
+    return false;
+  // Outline atomics for AArch64 are supported by compiler-rt
+  // and libgcc since 9.3.1
+  if (GetRuntimeLibType(Args) == ToolChain::RLT_Libgcc) {
+    const GCCVersion &Ver = GCCInstallation.getVersion();
+    if (Ver.isOlderThan(9, 3, 1))
+      return false;
+  } else if (GetRuntimeLibType(Args) != ToolChain::RLT_CompilerRT) {
+    return false;
+  }
+  return true;
+}
+
 bool Linux::isNoExecStackDefault() const {
     return getTriple().isAndroid();
 }