Skip the op replacement if the returned results are empty

[liufengdb]

add the erase op

[antiagainst]

Could you add a test for this? :)

mlir/tools/mlir-tblgen/RewriterGen.cpp

 //===- RewriterGen.cpp - MLIR pattern rewriter generator ------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
for (int i = replStartIndex; i < numResultPatterns; ++i) {
       // TODO(b/147096809): Revisit the need for materializing a vector.
       os << symbolInfoMap.getAllRangeUse(
           val,
           "    for (auto v : SmallVector<Value, 4>{ {0} }) {{ "
           "tblgen_repl_values.push_back(v); }",
           "\n");
     }
     os.indent(4) << "\n";
-    os.indent(4) << "rewriter.replaceOp(op0, tblgen_repl_values);\n";
+    // Skip the op replacement if the result pattern doesn't return results.
+    os.indent(4) << "if (tblgen_repl_values.empty())\n";
+    os.indent(4) << "  rewriter.replaceOp(op0, tblgen_repl_values);\n";
   }
 
   LLVM_DEBUG(llvm::dbgs() << "--- done emitting rewrite logic ---\n");
 }
 
 std::string PatternEmitter::getUniqueSymbol(const Operator *op) {
   return std::string(
       formatv("tblgen_{0}_{1}", op->getCppClassName(), nextValueId++));