Subzero. ARM32. Improve constant lowering.

src/IceUtils.h

 //===- subzero/src/IceUtils.h - Utility functions ---------------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
 /// This file declares some utility functions.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEUTILS_H
 #define SUBZERO_SRC_ICEUTILS_H
 
 #include <climits>
+#include <cmath> // std::signbit()
 
 namespace Ice {
 
 /// Similar to bit_cast, but allows copying from types of unrelated sizes. This
 /// method was introduced to enable the strict aliasing optimizations of GCC
 /// 4.4. Basically, GCC mindlessly relies on obscure details in the C++ standard
 /// that make reinterpret_cast virtually useless.
 template <class D, class S> inline D bit_copy(const S &source) {
   D destination;
   // This use of memcpy is safe: source and destination cannot overlap.
@@ skipping 81 matching lines @@
       return value;
     return (value << shift) | (value >> (32 - shift));
   }
 
   /// Rotate the value bit pattern to the right by shift bits.
   static inline uint32_t rotateRight32(uint32_t value, uint32_t shift) {
     if (shift == 0)
       return value;
     return (value >> shift) | (value << (32 - shift));
   }
+
+  /// Returns true if Val is +0.0. It requires T to be a floating point type.
+  template <typename T> static bool isPositiveZero(T Val) {
+    static_assert(std::is_floating_point<T>::value,
+                  "Input type must be floating point");
+    return Val == 0 && !std::signbit(Val);
+  }
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEUTILS_H