Subzero: Use a "deterministic" random shuffle for register allocation.

src/IceRNG.h

 //===- subzero/src/IceRNG.h - Random number generator -----------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares a random number generator.
@@ skipping 35 matching lines @@
 public:
   uint64_t operator()(uint64_t Max) { return RNG.next(Max); }
   bool getTrueWithProbability(float Probability);
   explicit RandomNumberGeneratorWrapper(RandomNumberGenerator &RNG)
       : RNG(RNG) {}
 
 private:
   RandomNumberGenerator &RNG;
 };
 
+// RandomShuffle is an implementation of std::random_shuffle() that
+// doesn't change across stdlib implementations.  Adapted from a
+// sample implementation at cppreference.com.
+template <class RandomIt, class RandomFunc>
+void RandomShuffle(RandomIt First, RandomIt Last, RandomFunc &&RNG) {
+  for (auto i = Last - First - 1; i > 0; --i)
+    std::swap(First[i], First[RNG(i + 1)]);
+}
+
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICERNG_H