diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index c953150..d4fe26e 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -373,6 +373,13 @@
       break;
     }
     break;
+  case Type::FixedWidthInt:
+    // FIXME: This isn't precisely correct; the width/alignment should depend
+    // on the available types for the target
+    Width = cast<FixedWidthIntType>(T)->getWidth();
+    Width = std::max(llvm::NextPowerOf2(Width - 1), 8ULL);
+    Align = Width;
+    break;
   case Type::ASQual:
     // FIXME: Pointers into different addr spaces could have different sizes and
     // alignment requirements: getPointerInfo should take an AddrSpace.
@@ -769,6 +776,14 @@
   return QualType(New, 0);
 }
 
+QualType ASTContext::getFixedWidthIntType(unsigned Width, bool Signed) {
+  llvm::DenseMap<unsigned, FixedWidthIntType*> &Map = Signed ?
+     SignedFixedWidthIntTypes : UnsignedFixedWidthIntTypes;
+  FixedWidthIntType *&Entry = Map[Width];
+  if (!Entry)
+    Entry = new FixedWidthIntType(Width, Signed);
+  return QualType(Entry, 0);
+}
 
 /// getPointerType - Return the uniqued reference to the type for a pointer to
 /// the specified type.
@@ -1599,32 +1614,39 @@
 /// getIntegerRank - Return an integer conversion rank (C99 6.3.1.1p1). This
 /// routine will assert if passed a built-in type that isn't an integer or enum,
 /// or if it is not canonicalized.
-static unsigned getIntegerRank(Type *T) {
+unsigned ASTContext::getIntegerRank(Type *T) {
   assert(T->isCanonical() && "T should be canonicalized");
-  if (isa<EnumType>(T))
-    return 4;
-  
+  if (EnumType* ET = dyn_cast<EnumType>(T))
+    T = ET->getDecl()->getIntegerType().getTypePtr();
+
+  // There are two things which impact the integer rank: the width, and
+  // the ordering of builtins.  The builtin ordering is encoded in the
+  // bottom three bits; the width is encoded in the bits above that.
+  if (FixedWidthIntType* FWIT = dyn_cast<FixedWidthIntType>(T)) {
+    return FWIT->getWidth() << 3;
+  }
+
   switch (cast<BuiltinType>(T)->getKind()) {
   default: assert(0 && "getIntegerRank(): not a built-in integer");
   case BuiltinType::Bool:
-    return 1;
+    return 1 + (getIntWidth(BoolTy) << 3);
   case BuiltinType::Char_S:
   case BuiltinType::Char_U:
   case BuiltinType::SChar:
   case BuiltinType::UChar:
-    return 2;
+    return 2 + (getIntWidth(CharTy) << 3);
   case BuiltinType::Short:
   case BuiltinType::UShort:
-    return 3;
+    return 3 + (getIntWidth(ShortTy) << 3);
   case BuiltinType::Int:
   case BuiltinType::UInt:
-    return 4;
+    return 4 + (getIntWidth(IntTy) << 3);
   case BuiltinType::Long:
   case BuiltinType::ULong:
-    return 5;
+    return 5 + (getIntWidth(LongTy) << 3);
   case BuiltinType::LongLong:
   case BuiltinType::ULongLong:
-    return 6;
+    return 6 + (getIntWidth(LongLongTy) << 3);
   }
 }
 
@@ -2718,7 +2740,10 @@
 unsigned ASTContext::getIntWidth(QualType T) {
   if (T == BoolTy)
     return 1;
-  // At the moment, only bool has padding bits
+  if (FixedWidthIntType* FWIT = dyn_cast<FixedWidthIntType>(T)) {
+    return FWIT->getWidth();
+  }
+  // For builtin types, just use the standard type sizing method
   return (unsigned)getTypeSize(T);
 }
 
diff --git a/lib/AST/Type.cpp b/lib/AST/Type.cpp
index 24cf853..ad5026b 100644
--- a/lib/AST/Type.cpp
+++ b/lib/AST/Type.cpp
@@ -510,6 +510,8 @@
     // FIXME: In C++, enum types are never integer types.
     if (TT->getDecl()->isEnum() && TT->getDecl()->isDefinition())
       return true;
+  if (isa<FixedWidthIntType>(CanonicalType))
+    return true;
   if (const VectorType *VT = dyn_cast<VectorType>(CanonicalType))
     return VT->getElementType()->isIntegerType();
   if (const ASQualType *ASQT = dyn_cast<ASQualType>(CanonicalType))
@@ -525,6 +527,8 @@
     if (TT->getDecl()->isEnum() && TT->getDecl()->isDefinition())
       return true;  // Complete enum types are integral.
                     // FIXME: In C++, enum types are never integral.
+  if (isa<FixedWidthIntType>(CanonicalType))
+    return true;
   if (const ASQualType *ASQT = dyn_cast<ASQualType>(CanonicalType))
     return ASQT->getBaseType()->isIntegralType();
   return false;
@@ -578,6 +582,10 @@
   if (const EnumType *ET = dyn_cast<EnumType>(CanonicalType))
     return ET->getDecl()->getIntegerType()->isSignedIntegerType();
   
+  if (const FixedWidthIntType *FWIT =
+          dyn_cast<FixedWidthIntType>(CanonicalType))
+    return FWIT->isSigned();
+  
   if (const VectorType *VT = dyn_cast<VectorType>(CanonicalType))
     return VT->getElementType()->isSignedIntegerType();
   if (const ASQualType *ASQT = dyn_cast<ASQualType>(CanonicalType))
@@ -598,6 +606,10 @@
   if (const EnumType *ET = dyn_cast<EnumType>(CanonicalType))
     return ET->getDecl()->getIntegerType()->isUnsignedIntegerType();
 
+  if (const FixedWidthIntType *FWIT =
+          dyn_cast<FixedWidthIntType>(CanonicalType))
+    return !FWIT->isSigned();
+
   if (const VectorType *VT = dyn_cast<VectorType>(CanonicalType))
     return VT->getElementType()->isUnsignedIntegerType();
   if (const ASQualType *ASQT = dyn_cast<ASQualType>(CanonicalType))
@@ -635,6 +647,8 @@
            BT->getKind() <= BuiltinType::LongDouble;
   if (const TagType *TT = dyn_cast<TagType>(CanonicalType))
     return TT->getDecl()->isEnum() && TT->getDecl()->isDefinition();
+  if (isa<FixedWidthIntType>(CanonicalType))
+    return true;
   if (const VectorType *VT = dyn_cast<VectorType>(CanonicalType))
     return VT->getElementType()->isRealType();
   if (const ASQualType *ASQT = dyn_cast<ASQualType>(CanonicalType))
@@ -650,6 +664,8 @@
     // GCC allows forward declaration of enum types (forbid by C99 6.7.2.3p2).
     // If a body isn't seen by the time we get here, return false.
     return ET->getDecl()->isDefinition();
+  if (isa<FixedWidthIntType>(CanonicalType))
+    return true;
   if (const ASQualType *ASQT = dyn_cast<ASQualType>(CanonicalType))
     return ASQT->getBaseType()->isArithmeticType();
   return isa<ComplexType>(CanonicalType) || isa<VectorType>(CanonicalType);
@@ -667,6 +683,8 @@
   }
   if (const ASQualType *ASQT = dyn_cast<ASQualType>(CanonicalType))
     return ASQT->getBaseType()->isScalarType();
+  if (isa<FixedWidthIntType>(CanonicalType))
+    return true;
   return isa<PointerType>(CanonicalType) ||
          isa<BlockPointerType>(CanonicalType) ||
          isa<MemberPointerType>(CanonicalType) ||
@@ -1014,6 +1032,21 @@
   }
 }
 
+void FixedWidthIntType::getAsStringInternal(std::string &S) const {
+  // FIXME: Once we get bitwidth attribute, write as
+  // "int __attribute__((bitwidth(x)))".
+  std::string prefix = "__clang_fixedwidth";
+  prefix += llvm::utostr_32(Width);
+  prefix += (char)(Signed ? 'S' : 'U');
+  if (S.empty()) {
+    S = prefix;
+  } else {
+    // Prefix the basic type, e.g. 'int X'.
+    S = prefix + S;
+  }
+}
+
+
 void ComplexType::getAsStringInternal(std::string &S) const {
   ElementType->getAsStringInternal(S);
   S = "_Complex " + S;
diff --git a/lib/CodeGen/CodeGenTypes.cpp b/lib/CodeGen/CodeGenTypes.cpp
index 37b7c5f..5c4b2a5 100644
--- a/lib/CodeGen/CodeGenTypes.cpp
+++ b/lib/CodeGen/CodeGenTypes.cpp
@@ -216,6 +216,8 @@
     }
     break;
   }
+  case Type::FixedWidthInt:
+    return llvm::IntegerType::get(cast<FixedWidthIntType>(T)->getWidth());
   case Type::Complex: {
     const llvm::Type *EltTy = 
       ConvertTypeRecursive(cast<ComplexType>(Ty).getElementType());
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index c27df2b..c08634c 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -1238,7 +1238,12 @@
     return;
   }
   
-  // FIXME: Need proper fixed-width types
+  // FIXME: Sync this with InitializePredefinedMacros; we need to match
+  // int8_t and friends, at least with glibc.
+  // FIXME: Make sure 32/64-bit integers don't get defined to types of
+  // the wrong width on unusual platforms.
+  // FIXME: Make sure floating-point mappings are accurate
+  // FIXME: Support XF and TF types
   QualType NewTy;
   switch (DestWidth) {
   case 0:
@@ -1277,6 +1282,12 @@
     else
       NewTy = S.Context.UnsignedLongLongTy;
     break;
+  case 128:
+    if (!IntegerMode) {
+      S.Diag(Attr.getLoc(), diag::err_unsupported_machine_mode) << Name;
+      return;
+    }
+    NewTy = S.Context.getFixedWidthIntType(128, OldTy->isSignedIntegerType());
   }
 
   if (!OldTy->getAsBuiltinType())