[LLVM] convergence verifier should visit all instructions (#66200)

The entry and loop intrinsics for convergence control cannot be preceded
by convergent operations in their respective basic blocks. To check
that, the verifier needs to reset its state at the start of the block.
This was missed in the previous commit
fa6dd7a.

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

@@ -363,7 +363,7 @@ class Verifier : public InstVisitor<Verifier>, VerifierSupport {
   SmallVector<const DILocalVariable *, 16> DebugFnArgs;
 
   TBAAVerifier TBAAVerifyHelper;
-  ConvergenceVerifier CV;
+  ConvergenceVerifier ConvergenceVerifyHelper;
 
   SmallVector<IntrinsicInst *, 4> NoAliasScopeDecls;
 
@@ -408,15 +408,15 @@ class Verifier : public InstVisitor<Verifier>, VerifierSupport {
     auto FailureCB = [this](const Twine &Message) {
       this->CheckFailed(Message);
     };
-    CV.initialize(OS, FailureCB, F);
+    ConvergenceVerifyHelper.initialize(OS, FailureCB, F);
 
     Broken = false;
     // FIXME: We strip const here because the inst visitor strips const.
     visit(const_cast<Function &>(F));
     verifySiblingFuncletUnwinds();
 
-    if (CV.sawTokens())
-      CV.verify(DT);
+    if (ConvergenceVerifyHelper.sawTokens())
+      ConvergenceVerifyHelper.verify(DT);
 
     InstsInThisBlock.clear();
     DebugFnArgs.clear();
@@ -2867,6 +2867,7 @@ void Verifier::visitFunction(const Function &F) {
 //
 void Verifier::visitBasicBlock(BasicBlock &BB) {
   InstsInThisBlock.clear();
+  ConvergenceVerifyHelper.visit(BB);
 
   // Ensure that basic blocks have terminators!
   Check(BB.getTerminator(), "Basic Block does not have terminator!", &BB);
@@ -3568,7 +3569,7 @@ void Verifier::visitCallBase(CallBase &Call) {
   if (Call.isInlineAsm())
     verifyInlineAsmCall(Call);
 
-  CV.visit(Call);
+  ConvergenceVerifyHelper.visit(Call);
 
   visitInstruction(Call);
 }

llvm/test/Verifier/convergencectrl-invalid.ll

@@ -126,13 +126,18 @@ define void @entry_in_convergent(i32 %x, i32 %y) {
 }
 
 ; CHECK: Loop intrinsic cannot be preceded by a convergent operation in the same basic block.
-; CHECK:   %t60_tok3
+; CHECK-NEXT: %h1
+; CHECK-SAME: %t60_tok3
 define void @loop_at_start(i32 %x, i32 %y) convergent {
 A:
   %t60_tok3 = call token @llvm.experimental.convergence.entry()
   br label %B
 B:
   %z = add i32 %x, %y
+  ; This is not an error
+  %h2 = call token @llvm.experimental.convergence.loop() [ "convergencectrl"(token %t60_tok3) ]
+  br label %C
+C:
   call void @f()
   %h1 = call token @llvm.experimental.convergence.loop() [ "convergencectrl"(token %t60_tok3) ]
   ret void