Index: include/clang/Basic/TargetInfo.h
===================================================================
--- include/clang/Basic/TargetInfo.h
+++ include/clang/Basic/TargetInfo.h
@@ -807,6 +807,13 @@
   // \brief Validate the contents of the __builtin_cpu_supports(const char*)
   // argument.
   virtual bool validateCpuSupports(StringRef Name) const { return false; }
+
+  /// Handle arguments passed to LLVM's option processing.
+  ///
+  /// \return False on error.
+  virtual bool handleLLVMArgs(std::vector<std::string> &Args) {
+    return true;
+  }
   
   // \brief Returns maximal number of args passed in registers.
   unsigned getRegParmMax() const {
Index: include/clang/Basic/TargetOptions.h
===================================================================
--- include/clang/Basic/TargetOptions.h
+++ include/clang/Basic/TargetOptions.h
@@ -47,6 +47,10 @@
   std::vector<std::string> Features;
   
   std::vector<std::string> Reciprocals;
+
+  /// \brief A list of arguments to forward to LLVM's option processing; this
+  /// should only be used for debugging and experimental features.
+  std::vector<std::string> LLVMArgs;
 };
 
 }  // end namespace clang
Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1300,6 +1300,7 @@
 def mno_rdseed : Flag<["-"], "mno-rdseed">, Group<m_x86_Features_Group>;
 def mno_adx : Flag<["-"], "mno-adx">, Group<m_x86_Features_Group>;
 def mno_sha : Flag<["-"], "mno-sha">, Group<m_x86_Features_Group>;
+def malign_double : Flag<["-"], "malign-double">,  Group<m_Group>;
 
 def munaligned_access : Flag<["-"], "munaligned-access">, Group<m_arm_Features_Group>,
   HelpText<"Allow memory accesses to be unaligned (AArch32/AArch64 only)">;
Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -723,7 +723,7 @@
     if (Triple.getArch() == llvm::Triple::arm) {
       // Handled in ARM's setABI().
     } else if (Triple.getArch() == llvm::Triple::x86) {
-      this->DataLayoutString = "e-m:e-p:32:32-i64:64-n8:16:32-S128";
+      // Handled in X86_32's setDataLayoutString.
     } else if (Triple.getArch() == llvm::Triple::x86_64) {
       this->DataLayoutString = "e-m:e-p:32:32-i64:64-n8:16:32:64-S128";
     } else if (Triple.getArch() == llvm::Triple::mipsel) {
@@ -3569,13 +3569,21 @@
 
 // X86-32 generic target
 class X86_32TargetInfo : public X86TargetInfo {
+  virtual void setDataLayoutString() {
+    if (getTriple().isOSNaCl())
+      DataLayoutString = "e-m:e-p:32:32-i64:64-n8:16:32-S128";
+    else if (HasAlignedDouble)
+      DataLayoutString = "e-m:e-p:32:32-i64:64-f80:32-n8:16:32-S128";
+    else
+      DataLayoutString = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128";
+  }
+  bool HasAlignedDouble;
 public:
   X86_32TargetInfo(const llvm::Triple &Triple) : X86TargetInfo(Triple) {
     DoubleAlign = LongLongAlign = 32;
     LongDoubleWidth = 96;
     LongDoubleAlign = 32;
     SuitableAlign = 128;
-    DataLayoutString = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128";
     SizeType = UnsignedInt;
     PtrDiffType = SignedInt;
     IntPtrType = SignedInt;
@@ -3620,6 +3628,16 @@
 
     return X86TargetInfo::validateOperandSize(Constraint, Size);
   }
+
+  bool handleLLVMArgs(std::vector<std::string> &Args) override {
+    HasAlignedDouble = false;
+    auto it = std::find(Args.begin(), Args.end(), "-malign-double");
+    if (it != Args.end()) {
+      HasAlignedDouble = true;
+    }
+    setDataLayoutString();
+    return true;
+  }
 };
 
 class NetBSDI386TargetInfo : public NetBSDTargetInfo<X86_32TargetInfo> {
@@ -3659,6 +3677,9 @@
 };
 
 class DarwinI386TargetInfo : public DarwinTargetInfo<X86_32TargetInfo> {
+  void setDataLayoutString() override {
+    DataLayoutString = "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128";
+  }
 public:
   DarwinI386TargetInfo(const llvm::Triple &Triple)
       : DarwinTargetInfo<X86_32TargetInfo>(Triple) {
@@ -3667,7 +3688,6 @@
     SuitableAlign = 128;
     SizeType = UnsignedLong;
     IntPtrType = SignedLong;
-    DataLayoutString = "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128";
     HasAlignMac68kSupport = true;
   }
 
@@ -3685,17 +3705,19 @@
 
 // x86-32 Windows target
 class WindowsX86_32TargetInfo : public WindowsTargetInfo<X86_32TargetInfo> {
-public:
-  WindowsX86_32TargetInfo(const llvm::Triple &Triple)
-      : WindowsTargetInfo<X86_32TargetInfo>(Triple) {
-    WCharType = UnsignedShort;
-    DoubleAlign = LongLongAlign = 64;
+  void setDataLayoutString() override {
     bool IsWinCOFF =
         getTriple().isOSWindows() && getTriple().isOSBinFormatCOFF();
     DataLayoutString = IsWinCOFF
                            ? "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
                            : "e-m:e-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32";
   }
+public:
+  WindowsX86_32TargetInfo(const llvm::Triple &Triple)
+      : WindowsTargetInfo<X86_32TargetInfo>(Triple) {
+    WCharType = UnsignedShort;
+    DoubleAlign = LongLongAlign = 64;
+  }
   void getTargetDefines(const LangOptions &Opts,
                         MacroBuilder &Builder) const override {
     WindowsTargetInfo<X86_32TargetInfo>::getTargetDefines(Opts, Builder);
@@ -3770,13 +3792,15 @@
 
 // x86-32 Cygwin target
 class CygwinX86_32TargetInfo : public X86_32TargetInfo {
+  void setDataLayoutString() override {
+    DataLayoutString = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32";
+  }
 public:
   CygwinX86_32TargetInfo(const llvm::Triple &Triple)
       : X86_32TargetInfo(Triple) {
     TLSSupported = false;
     WCharType = UnsignedShort;
     DoubleAlign = LongLongAlign = 64;
-    DataLayoutString = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32";
   }
   void getTargetDefines(const LangOptions &Opts,
                         MacroBuilder &Builder) const override {
@@ -7778,5 +7802,8 @@
   if (!Target->handleTargetFeatures(Opts->Features, Diags))
     return nullptr;
 
+  if (!Target->handleLLVMArgs(Opts->LLVMArgs))
+    return nullptr;
+
   return Target.release();
 }
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -1911,6 +1911,11 @@
           << A->getOption().getName() << Value;
     }
   }
+
+  if (Args.getLastArg(options::OPT_malign_double)) {
+    CmdArgs.push_back("-mllvm");
+    CmdArgs.push_back("-malign-double");
+  }
 }
 
 void Clang::AddHexagonTargetArgs(const ArgList &Args,
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -1867,6 +1867,7 @@
   Opts.LinkerVersion = Args.getLastArgValue(OPT_target_linker_version);
   Opts.Triple = llvm::Triple::normalize(Args.getLastArgValue(OPT_triple));
   Opts.Reciprocals = Args.getAllArgValues(OPT_mrecip_EQ);
+  Opts.LLVMArgs = Args.getAllArgValues(OPT_mllvm);
   // Use the default target triple if unspecified.
   if (Opts.Triple.empty())
     Opts.Triple = llvm::sys::getDefaultTargetTriple();
Index: test/Driver/malign-double.c
===================================================================
--- /dev/null
+++ test/Driver/malign-double.c
@@ -0,0 +1,22 @@
+// RUN: %clang -v -c -malign-double %s -target i686-unknown-linux 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-I686 %s
+
+// CHECK-I686: -cc1
+// CHECK-I686: -mllvm -malign-double
+// CHECK-I686-NOT: backend data layout {{'[^']+'}} does not match expected target description {{'[^']+'}}
+
+// RUN: %clang -v -c -malign-double %s -target x86_64-unknown-linux 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-X86_64 %s
+
+// CHECK-X86_64: -cc1
+// CHECK-X86_64: -mllvm -malign-double
+
+// RUN: not %clang -v -c -mno-align-double %s -target i686-unknown-linux 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-I686 %s
+
+// CHECK-NO-I686: unknown argument: '-mno-align-double'
+
+// RUN: not %clang -v -c -mno-align-double %s -target x86_64-unknown-linux 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-X86_64 %s
+
+// CHECK-NO-X86_64: unknown argument: '-mno-align-double'