[mlir] Add an assertion on creating an Operation with null result types

Null types are commonly used as an error marker. Catch them in the constructor
of Operation if they are present in the result type list, as otherwise this
could lead to further surprising behavior when querying op result types.

Fix AsyncToLLVM and StandardToLLVM that were using null types when constructing
operations.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D91770

mlir/lib/Conversion/AsyncToLLVM/AsyncToLLVM.cpp

@@ -223,7 +223,7 @@ static void addResumeFunction(ModuleOp module) {
   auto *block = resumeOp.addEntryBlock();
   OpBuilder blockBuilder = OpBuilder::atBlockEnd(block);
 
-  blockBuilder.create<LLVM::CallOp>(loc, Type(),
+  blockBuilder.create<LLVM::CallOp>(loc, TypeRange(),
                                     blockBuilder.getSymbolRefAttr(kCoroResume),
                                     resumeOp.getArgument(0));
 
@@ -343,7 +343,8 @@ static CoroMachinery setupCoroMachinery(FuncOp func) {
       ValueRange({coroId.getResult(0), coroHdl.getResult(0)}));
 
   // Free the memory.
-  builder.create<LLVM::CallOp>(loc, Type(), builder.getSymbolRefAttr(kFree),
+  builder.create<LLVM::CallOp>(loc, TypeRange(),
+                               builder.getSymbolRefAttr(kFree),
                                ValueRange(coroMem.getResult(0)));
   // Branch into the suspend block.
   builder.create<BranchOp>(loc, suspendBlock);
@@ -503,7 +504,7 @@ outlineExecuteOp(SymbolTable &symbolTable, ExecuteOp execute) {
 
   // Call async runtime API to execute a coroutine in the managed thread.
   SmallVector<Value, 2> executeArgs = {coro.coroHandle, resumePtr.res()};
-  builder.create<CallOp>(loc, Type(), kExecute, executeArgs);
+  builder.create<CallOp>(loc, TypeRange(), kExecute, executeArgs);
 
   // Split the entry block before the terminator.
   Block *resume = addSuspensionPoint(coro, coroSave.getResult(0),
@@ -524,7 +525,7 @@ outlineExecuteOp(SymbolTable &symbolTable, ExecuteOp execute) {
   // to async runtime to emplace the result token.
   for (Operation &op : execute.body().getOps()) {
     if (isa<async::YieldOp>(op)) {
-      builder.create<CallOp>(loc, kEmplaceToken, Type(), coro.asyncToken);
+      builder.create<CallOp>(loc, kEmplaceToken, TypeRange(), coro.asyncToken);
       continue;
     }
     builder.clone(op, valueMapping);
@@ -671,7 +672,7 @@ public:
     // Inside regular function we convert await operation to the blocking
     // async API await function call.
     if (!isInCoroutine)
-      rewriter.create<CallOp>(loc, Type(), blockingAwaitFuncName,
+      rewriter.create<CallOp>(loc, TypeRange(), blockingAwaitFuncName,
                               ValueRange(op->getOperand(0)));
 
     // Inside the coroutine we convert await operation into coroutine suspension
@@ -696,7 +697,7 @@ public:
       // the async await argument becomes ready.
       SmallVector<Value, 3> awaitAndExecuteArgs = {
           await.getOperand(), coro.coroHandle, resumePtr.res()};
-      builder.create<CallOp>(loc, Type(), coroAwaitFuncName,
+      builder.create<CallOp>(loc, TypeRange(), coroAwaitFuncName,
                              awaitAndExecuteArgs);
 
       // Split the entry block before the await operation.

mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp

@@ -2290,7 +2290,7 @@ struct CallOpInterfaceLowering : public ConvertOpToLLVMPattern<CallOpType> {
     auto callOp = cast<CallOpType>(op);
 
     // Pack the result types into a struct.
-    Type packedResult;
+    Type packedResult = nullptr;
     unsigned numResults = callOp.getNumResults();
     auto resultTypes = llvm::to_vector<4>(callOp.getResultTypes());
 
@@ -2302,8 +2302,9 @@ struct CallOpInterfaceLowering : public ConvertOpToLLVMPattern<CallOpType> {
 
     auto promoted = this->typeConverter.promoteOperands(
         op->getLoc(), /*opOperands=*/op->getOperands(), operands, rewriter);
-    auto newOp = rewriter.create<LLVM::CallOp>(op->getLoc(), packedResult,
-                                               promoted, op->getAttrs());
+    auto newOp = rewriter.create<LLVM::CallOp>(
+        op->getLoc(), packedResult ? TypeRange(packedResult) : TypeRange(),
+        promoted, op->getAttrs());
 
     SmallVector<Value, 4> results;
     if (numResults < 2) {

mlir/lib/IR/Operation.cpp

@@ -167,6 +167,8 @@ Operation::Operation(Location location, OperationName name,
     : location(location), numSuccs(numSuccessors), numRegions(numRegions),
       hasOperandStorage(hasOperandStorage), hasSingleResult(false), name(name),
       attrs(attributes) {
+  assert(llvm::all_of(resultTypes, [](Type t) { return t; }) &&
+         "unexpected null result type");
   if (!resultTypes.empty()) {
     // If there is a single result it is stored in-place, otherwise use a tuple.
     hasSingleResult = resultTypes.size() == 1;

mlir/lib/IR/TypeRange.cpp

@@ -14,7 +14,10 @@ using namespace mlir;
 // TypeRange
 
 TypeRange::TypeRange(ArrayRef<Type> types)
-    : TypeRange(types.data(), types.size()) {}
+    : TypeRange(types.data(), types.size()) {
+  assert(llvm::all_of(types, [](Type t) { return t; }) &&
+         "attempting to construct a TypeRange with null types");
+}
 TypeRange::TypeRange(OperandRange values)
     : TypeRange(values.begin().getBase(), values.size()) {}
 TypeRange::TypeRange(ResultRange values)

mlir/test/Conversion/StandardToLLVM/standard-to-llvm.mlir

@@ -203,3 +203,13 @@ func @get_gv3_memref() {
   return
 }
 
+// This should not trigger an assertion by creating an LLVM::CallOp with a
+// nullptr result type.
+
+// CHECK-LABEL: @call_zero_result_func
+func @call_zero_result_func() {
+  // CHECK: call @zero_result_func
+  call @zero_result_func() : () -> ()
+  return
+}
+func private @zero_result_func()