builder: return the operation type from the create method

This closes the door to on-the-fly folding, but that's unlikely to apply
to dialect ops any time soon.

If it does, we could add a new createFold method.

Author: nhaehnle

example/ExampleMain.cpp

@@ -107,10 +107,10 @@ void createFunctionExample(Module &module, const Twine &name) {
   Value *y3 = b.create<xd::ExtractElementOp>(y1, b.getInt32(2));
   Value *y4 = b.CreateAdd(y2, y3);
   Value *y5 = b.create<xd::InsertElementOp>(q2, y4, x1);
-  Value *y6 = b.create<xd::InsertElementOp>(y5, y2, b.getInt32(5));
+  auto *y6 = b.create<xd::InsertElementOp>(y5, y2, b.getInt32(5));
   b.create<xd::WriteOp>(y6);
 
-  cast<xd::InsertElementOp>(y6)->setIndex(b.getInt32(1));
+  y6->setIndex(b.getInt32(1));
 
   Value *p1 = b.create<xd::ReadOp>(b.getPtrTy(0));
   Value *p2 = b.create<xd::StreamAddOp>(p1, b.getInt64(14), b.getInt8(0));

include/llvm-dialects/Dialect/Builder.h

@@ -41,8 +41,7 @@ class Builder : public llvm::IRBuilder<> {
   template <typename DialectT>
   DialectT& getDialect() const {return m_dialects.getDialect<DialectT>();}
 
-  template <typename Op, typename ...Args>
-  llvm::Instruction *create(Args&&... args) {
+  template <typename Op, typename... Args> Op *create(Args &&...args) {
     Op *op = Op::create(*this, std::forward<Args>(args)...);
     assert(runInstructionVerifier([op](llvm::raw_ostream &errs) {
       return op->verifier(errs);