Index: include/clang/Basic/TargetOptions.h
===================================================================
--- include/clang/Basic/TargetOptions.h
+++ include/clang/Basic/TargetOptions.h
@@ -50,6 +50,10 @@
   std::vector<std::string> Features;
 
   std::vector<std::string> Reciprocals;
+
+  /// \brief Controls whether doubles and long longs should be aligned on two
+  // word boundaries.
+  bool AlignDouble;
 };
 
 }  // end namespace clang
Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1415,6 +1415,7 @@
 def mno_xsaves : Flag<["-"], "mno-xsaves">, Group<m_x86_Features_Group>;
 def mno_pku : Flag<["-"], "mno-pku">, 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)">;
 def mno_unaligned_access : Flag<["-"], "mno-unaligned-access">, Group<m_arm_Features_Group>,
Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -751,7 +751,7 @@
     if (Triple.getArch() == llvm::Triple::arm) {
       // Handled in ARM's setABI().
     } else if (Triple.getArch() == llvm::Triple::x86) {
-      this->resetDataLayout("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->resetDataLayout("e-m:e-p:32:32-i64:64-n8:16:32:64-S128");
     } else if (Triple.getArch() == llvm::Triple::mipsel) {
@@ -3767,7 +3767,15 @@
     LongDoubleWidth = 96;
     LongDoubleAlign = 32;
     SuitableAlign = 128;
-    resetDataLayout("e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128");
+
+    if (getTriple().isOSNaCl()) {
+      resetDataLayout("e-m:e-p:32:32-i64:64-n8:16:32-S128");
+    } else if (Opts.AlignDouble) {
+      resetDataLayout("e-m:e-p:32:32-i64:64-f80:32-n8:16:32-S128");
+    } else {
+      resetDataLayout("e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128");
+    }
+
     SizeType = UnsignedInt;
     PtrDiffType = SignedInt;
     IntPtrType = SignedInt;
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -2144,6 +2144,11 @@
     CmdArgs.push_back("soft");
     CmdArgs.push_back("-mstack-alignment=4");
   }
+
+  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
@@ -2091,6 +2091,9 @@
   Opts.LinkerVersion = Args.getLastArgValue(OPT_target_linker_version);
   Opts.Triple = llvm::Triple::normalize(Args.getLastArgValue(OPT_triple));
   Opts.Reciprocals = Args.getAllArgValues(OPT_mrecip_EQ);
+  auto LLVMArgs = Args.getAllArgValues(OPT_mllvm);
+  auto it = std::find(LLVMArgs.begin(), LLVMArgs.end(), "-malign-double");
+  Opts.AlignDouble = (it != LLVMArgs.end());
   // 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'