Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -1505,6 +1505,12 @@
   if (unsupportedTypeConversion(*this, LHSType, RHSType))
     return QualType();
 
+  // Comparison between the fixed point and floating point is unspecified.
+  // Reference N1169 4.1.4 (Type conversion, usual arithmetic conversions).
+  if ((LHSType->isFixedPointType() && RHSType->isRealFloatingType()) ||
+      (LHSType->isRealFloatingType() && RHSType->isFixedPointType()))
+    return QualType();
+
   // Handle complex types first (C99 6.3.1.8p1).
   if (LHSType->isComplexType() || RHSType->isComplexType())
     return handleComplexFloatConversion(*this, LHS, RHS, LHSType, RHSType,