[SafepointIRVerifier] NFC: Refactor code for identifying exclusive base type

Added a new Enum to identify if the base pointer is exclusively null or
exlusively some constant or not exclusively any constant.
Converted the base pointer identification method from recursive to
iterative form.

llvm-svn: 307340

llvm/lib/IR/SafepointIRVerifier.cpp

@@ -220,44 +220,75 @@ static void TransferBlock(const BasicBlock *BB,
         dbgs() << "\n";);
 }
 
-/// Return true if V is exclusively derived off a constant base, i.e. all
-/// operands of non-unary operators (phi/select) are derived off a constant
-/// base.
-static bool
-isExclusivelyConstantDerivedRecursive(const Value *V,
-                                      DenseSet<const Value *> &Visited) {
-  if (!Visited.insert(V).second)
-    return true;
+/// A given derived pointer can have multiple base pointers through phi/selects.
+/// This type indicates when the base pointer is exclusively constant
+/// (ExclusivelySomeConstant), and if that constant is proven to be exclusively
+/// null, we record that as ExclusivelyNull. In all other cases, the BaseType is
+/// NonConstant.
+enum BaseType {
+  NonConstant = 1, // Base pointers is not exclusively constant.
+  ExclusivelyNull,
+  ExclusivelySomeConstant // Base pointers for a given derived pointer is from a
+                          // set of constants, but they are not exclusively
+                          // null.
+};
 
-  if (isa<Constant>(V))
-    return true;
+/// Return the baseType for Val which states whether Val is exclusively
+/// derived from constant/null, or not exclusively derived from constant.
+/// Val is exclusively derived off a constant base when all operands of phi and
+/// selects are derived off a constant base.
+static enum BaseType getBaseType(const Value *Val) {
 
-  if (const auto *CI = dyn_cast<CastInst>(V))
-    return isExclusivelyConstantDerivedRecursive(CI->stripPointerCasts(),
-                                                 Visited);
+  SmallVector<const Value *, 32> Worklist;
+  DenseSet<const Value *> Visited;
+  bool isExclusivelyDerivedFromNull = true;
+  Worklist.push_back(Val);
+  // Strip through all the bitcasts and geps to get base pointer. Also check for
+  // the exclusive value when there can be multiple base pointers (through phis
+  // or selects).
+  while(!Worklist.empty()) {
+    const Value *V = Worklist.pop_back_val();
+    if (!Visited.insert(V).second)
+      continue;
 
-  if (const auto *GEP = dyn_cast<GetElementPtrInst>(V))
-    return isExclusivelyConstantDerivedRecursive(GEP->getPointerOperand(),
-                                                 Visited);
-
-  // All operands of the phi and select nodes should be derived off a constant
-  // base.
-  if (const auto *PN = dyn_cast<PHINode>(V)) {
-    return all_of(PN->incoming_values(), [&](const Value *InV) {
-      return isExclusivelyConstantDerivedRecursive(InV, Visited);
-    });
+    if (const auto *CI = dyn_cast<CastInst>(V)) {
+      Worklist.push_back(CI->stripPointerCasts());
+      continue;
+    }
+    if (const auto *GEP = dyn_cast<GetElementPtrInst>(V)) {
+      Worklist.push_back(GEP->getPointerOperand());
+      continue;
+    }
+    // Push all the incoming values of phi node into the worklist for
+    // processing.
+    if (const auto *PN = dyn_cast<PHINode>(V)) {
+      for (Value *InV: PN->incoming_values())
+        Worklist.push_back(InV);
+      continue;
+    }
+    if (const auto *SI = dyn_cast<SelectInst>(V)) {
+      // Push in the true and false values
+      Worklist.push_back(SI->getTrueValue());
+      Worklist.push_back(SI->getFalseValue());
+      continue;
+    }
+    if (isa<Constant>(V)) {
+      // We found at least one base pointer which is non-null, so this derived
+      // pointer is not exclusively derived from null.
+      if (V != Constant::getNullValue(V->getType()))
+        isExclusivelyDerivedFromNull = false;
+      // Continue processing the remaining values to make sure it's exclusively
+      // constant.
+      continue;
+    }
+    // At this point, we know that the base pointer is not exclusively
+    // constant.
+    return BaseType::NonConstant;
   }
-
-  if (const auto *SI = dyn_cast<SelectInst>(V))
-    return isExclusivelyConstantDerivedRecursive(SI->getTrueValue(), Visited) &&
-           isExclusivelyConstantDerivedRecursive(SI->getFalseValue(), Visited);
-
-  return false;
-}
-
-static bool isExclusivelyConstantDerived(const Value *V) {
-  DenseSet<const Value*> Visited;
-  return isExclusivelyConstantDerivedRecursive(V, Visited);
+  // Now, we know that the base pointer is exclusively constant, but we need to
+  // differentiate between exclusive null constant and non-null constant.
+  return isExclusivelyDerivedFromNull ? BaseType::ExclusivelyNull
+                                      : BaseType::ExclusivelySomeConstant;
 }
 
 static void Verify(const Function &F, const DominatorTree &DT) {
@@ -323,6 +354,10 @@ static void Verify(const Function &F, const DominatorTree &DT) {
     AnyInvalidUses = true;
   };
 
+  auto isNotExclusivelyConstantDerived = [](const Value *V) {
+    return getBaseType(V) == BaseType::NonConstant;
+  };
+
   for (const BasicBlock &BB : F) {
     // We destructively modify AvailableIn as we traverse the block instruction
     // by instruction.
@@ -334,14 +369,14 @@ static void Verify(const Function &F, const DominatorTree &DT) {
             const BasicBlock *InBB = PN->getIncomingBlock(i);
             const Value *InValue = PN->getIncomingValue(i);
 
-            if (!isExclusivelyConstantDerived(InValue) &&
+            if (isNotExclusivelyConstantDerived(InValue) &&
                 !BlockMap[InBB]->AvailableOut.count(InValue))
               ReportInvalidUse(*InValue, *PN);
           }
       } else {
         for (const Value *V : I.operands())
           if (containsGCPtrType(V->getType()) &&
-              !isExclusivelyConstantDerived(V) && !AvailableSet.count(V))
+              isNotExclusivelyConstantDerived(V) && !AvailableSet.count(V))
             ReportInvalidUse(*V, I);
       }