visit each basic block once to reset the first convergent op

Author: ssahasra

llvm/include/llvm/ADT/GenericConvergenceVerifier.h

@@ -40,6 +40,7 @@ template <typename ContextT> class GenericConvergenceVerifier {
   }
 
   void clear();
+  void visit(const BlockT &BB);
   void visit(const InstructionT &I);
   void verify(const DominatorTreeT &DT);
 

llvm/include/llvm/IR/GenericConvergenceVerifierImpl.h

@@ -67,17 +67,17 @@ template <class ContextT> void GenericConvergenceVerifier<ContextT>::clear() {
   ConvergenceKind = NoConvergence;
 }
 
+template <class ContextT>
+void GenericConvergenceVerifier<ContextT>::visit(const BlockT &BB) {
+  SeenFirstConvOp = false;
+}
+
 template <class ContextT>
 void GenericConvergenceVerifier<ContextT>::visit(const InstructionT &I) {
   auto ID = ContextT::getIntrinsicID(I);
   auto *TokenDef = findAndCheckConvergenceTokenUsed(I);
   bool IsCtrlIntrinsic = true;
 
-  // If this is the first instruction in the block, then we have not seen a
-  // convergent op yet.
-  if (!I.getPrevNode())
-    SeenFirstConvOp = false;
-
   switch (ID) {
   case Intrinsic::experimental_convergence_entry:
     Check(isInsideConvergentFunction(I),

llvm/lib/IR/Verifier.cpp

@@ -2875,6 +2875,7 @@ void Verifier::visitFunction(const Function &F) {
 //
 void Verifier::visitBasicBlock(BasicBlock &BB) {
   InstsInThisBlock.clear();
+  CV.visit(BB);
 
   // Ensure that basic blocks have terminators!
   Check(BB.getTerminator(), "Basic Block does not have terminator!", &BB);
@@ -3576,6 +3577,8 @@ void Verifier::visitCallBase(CallBase &Call) {
   if (Call.isInlineAsm())
     verifyInlineAsmCall(Call);
 
+  CV.visit(Call);
+
   visitInstruction(Call);
 }
 
@@ -4803,8 +4806,6 @@ void Verifier::visitInstruction(Instruction &I) {
   BasicBlock *BB = I.getParent();
   Check(BB, "Instruction not embedded in basic block!", &I);
 
-  CV.visit(I);
-
   if (!isa<PHINode>(I)) {   // Check that non-phi nodes are not self referential
     for (User *U : I.users()) {
       Check(U != (User *)&I || !DT.isReachableFromEntry(BB),