Remove useless check for ThreadModel==Single in ARMISelLowering. NFC.

ThreadModel::Single is already handled already by ARMPassConfig adding
LowerAtomicPass to the pass list, which lowers all atomics to non-atomic
ops and deletes fences.

So by the time we get to ISel, there's no atomic fences left, so they
don't need special handling.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265178 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/ARMISelLowering.cpp

@@ -843,14 +843,10 @@ ARMTargetLowering::ARMTargetLowering(const TargetMachine &TM,
     setOperationAction(ISD::DYNAMIC_STACKALLOC, MVT::i32, Expand);
 
   // ARMv6 Thumb1 (except for CPUs that support dmb / dsb) and earlier use
-  // the default expansion. If we are targeting a single threaded system,
-  // then set them all for expand so we can lower them later into their
-  // non-atomic form.
+  // the default expansion.
   InsertFencesForAtomic = false;
-  if (TM.Options.ThreadModel == ThreadModel::Single)
-    setOperationAction(ISD::ATOMIC_FENCE,   MVT::Other, Expand);
-  else if (Subtarget->hasAnyDataBarrier() && (!Subtarget->isThumb() ||
-                                              Subtarget->hasV8MBaselineOps())) {
+  if (Subtarget->hasAnyDataBarrier() &&
+      (!Subtarget->isThumb() || Subtarget->hasV8MBaselineOps())) {
     // ATOMIC_FENCE needs custom lowering; the others should have been expanded
     // to ldrex/strex loops already.
     setOperationAction(ISD::ATOMIC_FENCE,     MVT::Other, Custom);