[mlir][pdl] OperationOp should not be side-effect free

[Mogball]

Summary

Unbound OperationOp in the matcher (i.e. one with no uses) is already disallowed by the verifier. However, an OperationOp in the rewriter is not side-effect free -- it's creating an op!

[Mogball]

Fix diff .-.

[rriddle]

We will likely need to make these dynamic based on the situation, but LGTM for now.

mlir/include/mlir/Dialect/PDL/IR/PDLOps.td

let builders = [
     }]>,
   ];
 }
 
 //===----------------------------------------------------------------------===//
 // pdl::OperationOp
 //===----------------------------------------------------------------------===//
 
-def PDL_OperationOp
-    : PDL_Op<"operation", [AttrSizedOperandSegments, NoSideEffect]> {
+def PDL_OperationOp : PDL_Op<"operation", [AttrSizedOperandSegments]> {
   let summary = "Define an operation within a pattern";
   let description = [{
     `pdl.operation` operations define operation nodes within a pattern. Within
     a match sequence, i.e. when directly nested within a `pdl.pattern`, these
     operations correspond to input operations, or those that already existing
     within the MLIR module. Inside of a `pdl.rewrite`, these operations
     correspond to operations that should be created as part of the replacement
     sequence.

mlir/test/Conversion/PDLToPDLInterp/pdl-to-pdl-interp-rewriter.mlir

pdl.pattern : benefit(1) {
     %type = pdl.type
     %root = pdl.operation "foo.op" -> (%type : !pdl.type)
     pdl.rewrite %root {
       %newType = pdl.apply_native_rewrite "functor"[true](%root : !pdl.operation) : !pdl.type
       %newOp = pdl.operation "foo.op" -> (%newType : !pdl.type)
     }
   }
 }
+
+// -----
+
+// CHECK-LABEL: module @unbound_rewrite_op
+module @unbound_rewrite_op {
+  // CHECK: module @rewriters
+  // CHECK:   func @pdl_generated_rewriter()
+  // CHECK:     %[[UNUSED:.*]] = pdl_interp.create_operation "bar.op"
+  // CHECK:     pdl_interp.finalize
+  pdl.pattern : benefit(1) {
+    %root = pdl.operation "foo.op"
+    pdl.rewrite %root {
+      %unused = pdl.operation "bar.op"
+    }
+  }
+}
+
+// -----

mlir/test/Dialect/PDL/canonicalize.mlir

+// RUN: mlir-opt -canonicalize %s | FileCheck %s
+
+pdl.pattern @operation_op : benefit(1) {
+  %root = pdl.operation "foo.op"
+  pdl.rewrite %root {
+    // CHECK: pdl.operation "bar.unused"
+    %unused_rewrite = pdl.operation "bar.unused"
+    pdl.erase %root
+  }
+}