Use separate random number generator for each randomization pass

src/IceTargetLoweringX8664Traits.h

Index: src/IceTargetLoweringX8664Traits.h
diff --git a/src/IceTargetLoweringX8664Traits.h b/src/IceTargetLoweringX8664Traits.h
index 4a1200415bc55cc2cb47782289e9212960facdc7..c2a9729dc4e05b6a51693969d1ebbd0f0256ef70 100644
--- a/src/IceTargetLoweringX8664Traits.h
+++ b/src/IceTargetLoweringX8664Traits.h
@@ -406,13 +406,18 @@ template <> struct MachineTraits<TargetX8664> {
     REGX8664_TABLE
 #undef X
 
-    RandomNumberGeneratorWrapper RNG(Ctx->getRNG());
+    // Create a random number generator for regalloc randomization.
+    // Use function's sequence as the salt.
+    RandomNumberGenerator RNG(Ctx->getFlags().getRandomSeed(),
+                              RS_RegAllocRandomization,
+                              Func->getSequenceNumber());
+    RandomNumberGeneratorWrapper RNGW(RNG);
 
     // Shuffle the resulting equivalence classes.
     for (auto I : EquivalenceClasses) {
       const RegisterList &List = I.second;
       RegisterList Shuffled(List);
-      RandomShuffle(Shuffled.begin(), Shuffled.end(), RNG);
+      RandomShuffle(Shuffled.begin(), Shuffled.end(), RNGW);
       for (size_t SI = 0, SE = Shuffled.size(); SI < SE; ++SI) {
         Permutation[List[SI]] = Shuffled[SI];
         ++NumShuffled;