Index: include/clang/Basic/TargetOptions.h
===================================================================
--- include/clang/Basic/TargetOptions.h
+++ include/clang/Basic/TargetOptions.h
@@ -54,6 +54,10 @@
   std::vector<std::string> Features;
 
   std::vector<std::string> Reciprocals;
+
+  /// \brief Controls whether doubles and long longs should be aligned on two
+  /// word boundaries (x86 only).
+  bool AlignDouble;
 };
 
 }  // end namespace clang
Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1320,6 +1320,8 @@
 def mieee_fp : Flag<["-"], "mieee-fp">, Group<clang_ignored_m_Group>;
 def minline_all_stringops : Flag<["-"], "minline-all-stringops">, Group<clang_ignored_m_Group>;
 def mno_inline_all_stringops : Flag<["-"], "mno-inline-all-stringops">, Group<clang_ignored_m_Group>;
+def malign_double : Flag<["-"], "malign-double">, Group<m_Group>, Flags<[CC1Option]>,
+  HelpText<"Align doubles to two words in structs (x86 only)">;
 def mfloat_abi_EQ : Joined<["-"], "mfloat-abi=">, Group<m_Group>;
 def mfpmath_EQ : Joined<["-"], "mfpmath=">, Group<m_Group>;
 def mfpu_EQ : Joined<["-"], "mfpu=">, Group<m_Group>;
Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -3825,9 +3825,14 @@
 public:
   X86_32TargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : X86TargetInfo(Triple, Opts) {
-    DoubleAlign = LongLongAlign = 32;
+    if (Opts.AlignDouble) {
+      DoubleAlign = LongLongAlign = 64;
+      LongDoubleAlign = 64;
+    } else {
+      DoubleAlign = LongLongAlign = 32;
+      LongDoubleAlign = 32;
+    }
     LongDoubleWidth = 96;
-    LongDoubleAlign = 32;
     SuitableAlign = 128;
     resetDataLayout("e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128");
     SizeType = UnsignedInt;
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -2091,6 +2091,8 @@
   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.AlignDouble = Args.hasArg(OPT_malign_double);
+
   // Use the default target triple if unspecified.
   if (Opts.Triple.empty())
     Opts.Triple = llvm::sys::getDefaultTargetTriple();
Index: test/CodeGen/malign-double.cpp
===================================================================
--- /dev/null
+++ test/CodeGen/malign-double.cpp
@@ -0,0 +1,115 @@
+// RUN: %clang_cc1 -malign-double -triple i386-unknown-linux -emit-llvm %s -o - \
+// RUN:   | FileCheck --check-prefix=CHECK-ON --check-prefix=CHECK %s
+
+// RUN: %clang_cc1 -triple i386-unknown-linux -emit-llvm %s -o - \
+// RUN:   | FileCheck --check-prefix=CHECK-OFF --check-prefix=CHECK %s
+
+/* Structs S1, S2, S3, S4, and union U5 are taken from Intel, "IA-64
+   Software Conventions and Runtime Architecture Guide", version of
+   August 1999, Section 4.2, Figures 4-1 through 4-5.
+   A Union containing a double was also thrown in for good measure. */
+
+struct S1 {
+  char c;
+};
+
+unsigned S1_align = __alignof(struct S1);
+unsigned S1_size = sizeof(struct S1);
+// CHECK: @S1_align = global i32 1, align 4
+// CHECK: @S1_size = global i32 1, align 4
+
+unsigned S1_c_offset = (unsigned) &((struct S1*) 0)->c;
+// CHECK: @S1_c_offset = global i32 0, align 4
+
+struct S2{
+  char c;
+  char d;
+  short s;
+  int n;
+};
+
+unsigned S2_align = __alignof(struct S2);
+unsigned S2_size = sizeof(struct S2);
+// CHECK: @S2_align = global i32 4, align 4
+// CHECK: @S2_size = global i32 8, align 4
+
+unsigned S2_c_offset = (unsigned) &((struct S2*) 0)->c;
+unsigned S2_d_offset = (unsigned) &((struct S2*) 0)->d;
+unsigned S2_s_offset = (unsigned) &((struct S2*) 0)->s;
+unsigned S2_n_offset = (unsigned) &((struct S2*) 0)->n;
+// CHECK: @S2_c_offset = global i32 0, align 4
+// CHECK: @S2_d_offset = global i32 1, align 4
+// CHECK: @S2_s_offset = global i32 2, align 4
+// CHECK: @S2_n_offset = global i32 4, align 4
+
+struct S3 {
+  char c;
+  short s;
+};
+
+unsigned S3_align = __alignof(struct S3);
+unsigned S3_size = sizeof(struct S3);
+// CHECK: @S3_align = global i32 2, align 4
+// CHECK: @S3_size = global i32 4, align 4
+
+unsigned S3_c_offset = (unsigned) &((struct S3*) 0)->c;
+unsigned S3_s_offset = (unsigned) &((struct S3*) 0)->s;
+// CHECK: @S3_c_offset = global i32 0, align 4
+// CHECK: @S3_s_offset = global i32 2, align 4
+
+struct S4 {
+  char c;
+  double d;
+  short s;
+};
+
+unsigned S4_align = __alignof(struct S4);
+unsigned S4_size = sizeof(struct S4);
+// CHECK-ON: @S4_align = global i32 8, align 4
+// CHECK-ON: @S4_size = global i32 24, align 4
+// CHECK-OFF: @S4_align = global i32 4, align 4
+// CHECK-OFF: @S4_size = global i32 16, align 4
+
+unsigned S4_c_offset = (unsigned) &((struct S4*) 0)->c;
+unsigned S4_d_offset = (unsigned) &((struct S4*) 0)->d;
+unsigned S4_s_offset = (unsigned) &((struct S4*) 0)->s;
+// CHECK: @S4_c_offset = global i32 0, align 4
+// CHECK-ON: @S4_d_offset = global i32 8, align 4
+// CHECK-ON: @S4_s_offset = global i32 16, align 4
+// CHECK-OFF: @S4_d_offset = global i32 4, align 4
+// CHECK-OFF: @S4_s_offset = global i32 12, align 4
+
+union S5 {
+  char c;
+  short s;
+  int j;
+};
+
+unsigned S5_align = __alignof(union S5);
+unsigned S5_size = sizeof(union S5);
+// CHECK: @S5_align = global i32 4, align 4
+// CHECK: @S5_size = global i32 4, align 4
+
+unsigned S5_c_offset = (unsigned) &((union S5*) 0)->c;
+unsigned S5_s_offset = (unsigned) &((union S5*) 0)->s;
+unsigned S5_j_offset = (unsigned) &((union S5*) 0)->j;
+// CHECK: @S5_c_offset = global i32 0, align 4
+// CHECK: @S5_s_offset = global i32 0, align 4
+// CHECK: @S5_j_offset = global i32 0, align 4
+
+union S6 {
+  char c;
+  double d;
+};
+
+unsigned S6_align = __alignof(union S6);
+unsigned S6_size = sizeof(union S6);
+// CHECK-ON: @S6_align = global i32 8, align 4
+// CHECK-ON: @S6_size = global i32 8, align 4
+// CHECK-OFF: @S6_align = global i32 4, align 4
+// CHECK-OFF: @S6_size = global i32 8, align 4
+
+unsigned S6_c_offset = (unsigned) &((union S6*) 0)->c;
+unsigned S6_d_offset = (unsigned) &((union S6*) 0)->d;
+// CHECK: @S6_c_offset = global i32 0, align 4
+// CHECK: @S6_d_offset = global i32 0, align 4