Subzero. Buildable, non-functional TargetLoweringX8664.

src/IceTargetLoweringX86Base.h

Index: src/IceTargetLoweringX86Base.h
diff --git a/src/IceTargetLoweringX86Base.h b/src/IceTargetLoweringX86Base.h
index 58de7217571b44e0d0898e176380e9962326a54b..f88e8da68a146d1b2abc7e6edc7607914702ffbd 100644
--- a/src/IceTargetLoweringX86Base.h
+++ b/src/IceTargetLoweringX86Base.h
@@ -339,11 +339,25 @@ protected:
   void _divss(Variable *Dest, Operand *Src0) {
     Context.insert(Traits::Insts::Divss::create(Func, Dest, Src0));
   }
-  void _fld(Operand *Src0) {
-    Context.insert(Traits::Insts::Fld::create(Func, Src0));
-  }
-  void _fstp(Variable *Dest) {
-    Context.insert(Traits::Insts::Fstp::create(Func, Dest));
+  template <typename T = Traits>
+  typename std::enable_if<T::UsesX87, void>::type _fld(Operand *Src0) {
+    Context.insert(Traits::Insts::template Fld<>::create(Func, Src0));
+  }
+  // TODO(jpp): when implementing the X8664 calling convention, make sure x8664
+  // does not invoke this method, and remove it.
+  template <typename T = Traits>
+  typename std::enable_if<!T::UsesX87, void>::type _fld(Operand *) {
+    llvm::report_fatal_error("fld is not available in x86-64");
+  }
+  template <typename T = Traits>
+  typename std::enable_if<T::UsesX87, void>::type _fstp(Variable *Dest) {
+    Context.insert(Traits::Insts::template Fstp<>::create(Func, Dest));
+  }
+  // TODO(jpp): when implementing the X8664 calling convention, make sure x8664
+  // does not invoke this method, and remove it.
+  template <typename T = Traits>
+  typename std::enable_if<!T::UsesX87, void>::type _fstp(Variable *) {
+    llvm::report_fatal_error("fstp is not available in x86-64");
   }
   void _idiv(Variable *Dest, Operand *Src0, Operand *Src1) {
     Context.insert(Traits::Insts::Idiv::create(Func, Dest, Src0, Src1));