Remove InstCombineAtomicRMW.cpp piece for now.

Remove AtomicExpandPass.cpp idempotency optimisation change.

Author: anjenner

llvm/lib/CodeGen/AtomicExpandPass.cpp

@@ -1564,8 +1564,6 @@ bool AtomicExpandImpl::isIdempotentRMW(AtomicRMWInst *RMWI) {
   case AtomicRMWInst::Sub:
   case AtomicRMWInst::Or:
   case AtomicRMWInst::Xor:
-  case AtomicRMWInst::USubCond:
-  case AtomicRMWInst::USubSat:
     return C->isZero();
   case AtomicRMWInst::And:
     return C->isMinusOne();

llvm/lib/Transforms/InstCombine/InstCombineAtomicRMW.cpp

@@ -41,8 +41,6 @@ bool isIdempotentRMW(AtomicRMWInst& RMWI) {
     case AtomicRMWInst::Sub:
     case AtomicRMWInst::Or:
     case AtomicRMWInst::Xor:
-    case AtomicRMWInst::USubCond:
-    case AtomicRMWInst::USubSat:
       return C->isZero();
     case AtomicRMWInst::And:
       return C->isMinusOne();