diff --git a/clang/Basic/TargetInfo.cpp b/clang/Basic/TargetInfo.cpp
index b4eb4fbb16ab..21925fd33e92 100644
--- a/clang/Basic/TargetInfo.cpp
+++ b/clang/Basic/TargetInfo.cpp
@@ -13,9 +13,13 @@
 
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/Diagnostic.h"
+#include <map>
 using namespace llvm;
 using namespace clang;
 
+void TargetInfoImpl::ANCHOR() {} // out-of-line virtual method for class.
+
+
 /// DiagnoseNonPortability - When a use of a non-portable target feature is
 /// used, this method emits the diagnostic and marks the translation unit as
 /// non-portable.
@@ -24,6 +28,112 @@ void TargetInfo::DiagnoseNonPortability(SourceLocation Loc, unsigned DiagKind) {
   if (Diag) Diag->Report(Loc, DiagKind);
 }
 
+/// GetTargetDefineMap - Get the set of target #defines in an associative
+/// collection for easy lookup.
+static void GetTargetDefineMap(const TargetInfoImpl *Target,
+                               std::map<std::string, std::string> &Map) {
+  std::vector<std::string> PrimaryDefines;
+  Target->getTargetDefines(PrimaryDefines);
+
+  while (!PrimaryDefines.empty()) {
+    const char *Str = PrimaryDefines.back().c_str();
+    if (const char *Equal = strchr(Str, '=')) {
+      // Split at the '='.
+      Map.insert(std::make_pair(std::string(Str, Equal),
+                                std::string(Equal+1,
+                                            Str+PrimaryDefines.back().size())));
+    } else {
+      // Remember "macroname=1".
+      Map.insert(std::make_pair(PrimaryDefines.back(), std::string("1")));
+    }
+    PrimaryDefines.pop_back();
+  }
+}
+
+/// getTargetDefines - Appends the target-specific #define values for this
+/// target set to the specified buffer.
+void TargetInfo::getTargetDefines(std::vector<char> &Buffer) {
+  // This is tricky in the face of secondary targets.  Specifically, 
+  // target-specific #defines that are present and identical across all
+  // secondary targets are turned into #defines, #defines that are present in
+  // the primary target but are missing or different in the secondary targets
+  // are turned into #define_target, and #defines that are not defined in the
+  // primary, but are defined in a secondary are turned into
+  // #define_other_target.  This allows the preprocessor to correctly track uses
+  // of target-specific macros.
+  
+  // Get the set of primary #defines.
+  std::map<std::string, std::string> PrimaryDefines;
+  GetTargetDefineMap(PrimaryTarget, PrimaryDefines);
+  
+  // Get the sets of secondary #defines.
+  std::vector<std::map<std::string, std::string> > SecondaryDefines;
+  SecondaryDefines.resize(SecondaryTargets.size());
+  for (unsigned i = 0, e = SecondaryTargets.size(); i != e; ++i)
+    GetTargetDefineMap(SecondaryTargets[i], SecondaryDefines[i]);
+
+  // Loop over all defines in the primary target, processing them until we run
+  // out.
+  while (!PrimaryDefines.empty()) {
+    std::string DefineName  = PrimaryDefines.begin()->first;
+    std::string DefineValue = PrimaryDefines.begin()->second;
+    PrimaryDefines.erase(PrimaryDefines.begin());
+    
+    // Check to see whether all secondary targets have this #define and whether
+    // it is to the same value.  Remember if not, but remove the #define from
+    // their collection in any case if they have it.
+    bool isPortable = true;
+    
+    for (unsigned i = 0, e = SecondaryDefines.size(); i != e; ++i) {
+      std::map<std::string, std::string>::iterator I = 
+        SecondaryDefines[i].find(DefineName);
+      if (I == SecondaryDefines[i].end()) {
+        // Secondary target doesn't have this #define.
+        isPortable = false;
+      } else {
+        // Secondary target has this define, remember if it disagrees.
+        if (isPortable)
+          isPortable = I->second == DefineValue;
+        // Remove it from the secondary target unconditionally.
+        SecondaryDefines[i].erase(I);
+      }
+    }
+    
+    // If this define is non-portable, turn it into #define_target, otherwise
+    // just use #define.
+    const char *Command = isPortable ? "#define " : "#define_target ";
+    Buffer.insert(Buffer.end(), Command, Command+strlen(Command));
+
+    // Insert "defname defvalue\n".
+    Buffer.insert(Buffer.end(), DefineName.begin(), DefineName.end());
+    Buffer.push_back(' ');
+    Buffer.insert(Buffer.end(), DefineValue.begin(), DefineValue.end());
+    Buffer.push_back('\n');
+  }
+  
+  // Now that all of the primary target's defines have been handled and removed
+  // from the secondary target's define sets, go through the remaining secondary
+  // target's #defines and taint them.
+  for (unsigned i = 0, e = SecondaryDefines.size(); i != e; ++i) {
+    std::map<std::string, std::string> &Defs = SecondaryDefines[i];
+    while (!Defs.empty()) {
+      const std::string &DefName = Defs.begin()->first;
+      
+      // Insert "#define_other_target defname".
+      const char *Command = "#define_other_target ";
+      Buffer.insert(Buffer.end(), Command, Command+strlen(Command));
+      Buffer.insert(Buffer.end(), DefName.begin(), DefName.end());
+      Buffer.push_back('\n');
+      
+      // If any other secondary targets have this same define, remove it from
+      // them to avoid duplicate #define_other_target directives.
+      for (unsigned j = i+1; j != e; ++j)
+        SecondaryDefines[j].erase(DefName);
+      
+      Defs.erase(Defs.begin());
+    }
+  }
+}
 
 /// ComputeWCharWidth - Determine the width of the wchar_t type for the primary
 /// target, diagnosing whether this is non-portable across the secondary
diff --git a/clang/include/clang/Basic/TargetInfo.h b/clang/include/clang/Basic/TargetInfo.h
index 7b6177fd26b1..26ccfcbd8d35 100644
--- a/clang/include/clang/Basic/TargetInfo.h
+++ b/clang/include/clang/Basic/TargetInfo.h
@@ -16,6 +16,7 @@
 
 #include "clang/Basic/SourceLocation.h"
 #include <vector>
+#include <string>
 
 namespace llvm {
 namespace clang {
@@ -85,6 +86,10 @@ public:
   
   ///===---- Target property query methods --------------------------------===//
   
+  /// getTargetDefines - Appends the target-specific #define values for this
+  /// target set to the specified buffer.
+  void getTargetDefines(std::vector<char> &DefineBuffer);
+  
   /// getWCharWidth - Return the size of wchar_t in bytes.
   ///
   unsigned getWCharWidth(SourceLocation Loc) {
@@ -108,11 +113,19 @@ protected:
   unsigned WCharWidth;    /// sizeof(wchar_t) in bytes.  Default value is 4.
 public:
   TargetInfoImpl() : WCharWidth(4) {}
+  virtual ~TargetInfoImpl() {}
   
+  /// getTargetDefines - Return a list of the target-specific #define values set
+  /// when compiling to this target.  Each string should be of the form "X",
+  /// which results in '#define X 1' or "X=Y" which results in "#define X Y"
+  virtual void getTargetDefines(std::vector<std::string> &Defines) const = 0;
+
   /// getWCharWidth - Return the size of wchar_t in bytes.
   ///
   unsigned getWCharWidth() const { return WCharWidth; }
   
+private:
+  virtual void ANCHOR(); // out-of-line virtual method for class.
 };
 
 }  // end namespace clang