Use separate random number generator for each randomization pass

src/IceRNG.cpp

Index: src/IceRNG.cpp
diff --git a/src/IceRNG.cpp b/src/IceRNG.cpp
index a6b9adf5b93bfb2b867ebc4ce3e84b33ec7a5e07..28efb8ffa14f432ce18d398f725afaa2a6199adb 100644
--- a/src/IceRNG.cpp
+++ b/src/IceRNG.cpp
@@ -31,6 +31,16 @@ constexpr unsigned MAX = 2147483647;
 RandomNumberGenerator::RandomNumberGenerator(uint64_t Seed, llvm::StringRef)
     : State(Seed) {}
 
+RandomNumberGenerator::RandomNumberGenerator(
+    uint64_t Seed, RandomizationPassesEnum RandomizationPassID, uint64_t Salt) {
+  constexpr unsigned NumBitsGlobalSeed = CHAR_BIT * sizeof(State);
+  constexpr unsigned NumBitsPassID = 4;
+  constexpr unsigned NumBitsSalt = 12;
+  static_assert(RPE_num < (1 << NumBitsPassID), "NumBitsPassID too small");
+  State = Seed ^ ((uint64_t)RandomizationPassID
+                  << (NumBitsGlobalSeed - NumBitsPassID)) ^
+          (Salt << (NumBitsGlobalSeed - NumBitsPassID - NumBitsSalt));
+}
 uint64_t RandomNumberGenerator::next(uint64_t Max) {
   // Lewis, Goodman, and Miller (1969)
   State = (16807 * State) % MAX;