[OpenMP] Fix carefully track SPMDCompatibilityTracker

[jdoerfert]

Summary

We did not properly use SPMDCompatibilityTracker in various places.
This patch makes sure we look at the validity properly and also fix
the state if we can.

[tianshilei1992]

LGTM.

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

void initialize(Attributor &A) override {
 
     Attributor::SimplifictionCallbackTy IsSPMDModeSimplifyCB =
         [&](const IRPosition &IRP, const AbstractAttribute *AA,
             bool &UsedAssumedInformation) -> Optional<Value *> {
       // IRP represents the "SPMDCompatibilityTracker" argument of an
       // __kmpc_target_init or
       // __kmpc_target_deinit call. We will answer this one with the internal
       // state.
-      if (!isValidState())
+      if (!SPMDCompatibilityTracker.isValidState())
         return nullptr;
       if (!SPMDCompatibilityTracker.isAtFixpoint()) {
         if (AA)
           A.recordDependence(*this, *AA, DepClassTy::OPTIONAL);
         UsedAssumedInformation = true;
       } else {
         UsedAssumedInformation = false;
       }
auto CheckRWInst = [&](Instruction &I) {
           return true;
       }
       // For now we give up on everything but stores.
       SPMDCompatibilityTracker.insert(&I);
       return true;
     };
 
     bool UsedAssumedInformationInCheckRWInst = false;
+    if (!SPMDCompatibilityTracker.isAtFixpoint())
       if (!A.checkForAllReadWriteInstructions(
               CheckRWInst, *this, UsedAssumedInformationInCheckRWInst))
         SPMDCompatibilityTracker.indicatePessimisticFixpoint();
 
     // Callback to check a call instruction.
+    bool AllSPMDStatesWereFixed = true;
     auto CheckCallInst = [&](Instruction &I) {
       auto &CB = cast<CallBase>(I);
       auto &CBAA = A.getAAFor<AAKernelInfo>(
           *this, IRPosition::callsite_function(CB), DepClassTy::OPTIONAL);
-      if (CBAA.getState().isValidState())
-        getState() ^= CBAA.getState();
+      AllSPMDStatesWereFixed &= CBAA.SPMDCompatibilityTracker.isAtFixpoint();
       return true;
     };
 
     bool UsedAssumedInformationInCheckCallInst = false;
     if (!A.checkForAllCallLikeInstructions(
             CheckCallInst, *this, UsedAssumedInformationInCheckCallInst))
       return indicatePessimisticFixpoint();
 
+    // If we haven't used any assumed information for the SPMD state we can fix
+    // it.
+    if (!UsedAssumedInformationInCheckRWInst &&
+        !UsedAssumedInformationInCheckCallInst && AllSPMDStatesWereFixed)
+      SPMDCompatibilityTracker.indicateOptimisticFixpoint();
+
     return StateBefore == getState() ? ChangeStatus::UNCHANGED
                                      : ChangeStatus::CHANGED;
   }
 };
 
 /// The call site kernel info abstract attribute, basically, what can we say
 /// about a call site with regards to the KernelInfoState. For now this simply
 /// forwards the information from the callee.