3 files changed, 18 insertions, 0 deletions
diff --git a/lib/AST/RecordLayoutBuilder.cpp b/lib/AST/RecordLayoutBuilder.cpp
index 97355dc04e..8e71588768 100644
--- a/lib/AST/RecordLayoutBuilder.cpp
+++ b/lib/AST/RecordLayoutBuilder.cpp
@@ -1211,6 +1211,11 @@ void RecordLayoutBuilder::InitializeLayout(const Decl *D) {
   
   IsMsStruct = D->hasAttr<MsStructAttr>();
 
+  // Honor the default struct packing maximum alignment flag.
+  if (unsigned DefaultMaxFieldAlignment = Context.getLangOptions().PackStruct) {
+    MaxFieldAlignment = CharUnits::fromQuantity(DefaultMaxFieldAlignment);
+  }
+
   // mac68k alignment supersedes maximum field alignment and attribute aligned,
   // and forces all structures to have 2-byte alignment. The IBM docs on it
   // allude to additional (more complicated) semantics, especially with regard
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index e193c0f505..1dcb8bc91d 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -2062,11 +2062,23 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                    false))
     CmdArgs.push_back("-fpascal-strings");
 
+  // Honor -fpack-struct= and -fpack-struct, if given. Note that
+  // -fno-pack-struct doesn't apply to -fpack-struct=.
+  if (Arg *A = Args.getLastArg(options::OPT_fpack_struct_EQ)) {
+    CmdArgs.push_back("-fpack-struct");
+    CmdArgs.push_back(A->getValue(Args));
+  } else if (Args.hasFlag(options::OPT_fpack_struct,
+                          options::OPT_fno_pack_struct, false)) {
+    CmdArgs.push_back("-fpack-struct");
+    CmdArgs.push_back("1");
+  }
+
   if (Args.hasArg(options::OPT_mkernel) ||
       Args.hasArg(options::OPT_fapple_kext)) {
     if (!Args.hasArg(options::OPT_fcommon))
       CmdArgs.push_back("-fno-common");
   }
+
   // -fcommon is default, only pass non-default.
   else if (!Args.hasFlag(options::OPT_fcommon, options::OPT_fno_common))
     CmdArgs.push_back("-fno-common");
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 5252ebadac..4fb3ee62f0 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -1728,6 +1728,7 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
     Args.hasArg(OPT_fobjc_default_synthesize_properties);
   Opts.CatchUndefined = Args.hasArg(OPT_fcatch_undefined_behavior);
   Opts.EmitAllDecls = Args.hasArg(OPT_femit_all_decls);
+  Opts.PackStruct = Args.getLastArgIntValue(OPT_fpack_struct, 0, Diags);
   Opts.PICLevel = Args.getLastArgIntValue(OPT_pic_level, 0, Diags);
   Opts.Static = Args.hasArg(OPT_static_define);
   Opts.DumpRecordLayouts = Args.hasArg(OPT_fdump_record_layouts);