ODS: provide a flag to skip generation of default build methods

Some operations need to override the default behavior of builders, in
particular region-holding operations such as affine.for or tf.graph want to
inject default terminators into the region upon construction, which default
builders won't do.  Provide a flag that disables the generation of default
builders so that the custom builders could use the same function signatures.
This is an intentionally low-level and heavy-weight feature that requires the
entire builder to be implemented, and it should be used sparingly.  Injecting
code into the end of a default builder would depend on the naming scheme of the
default builder arguments that is not visible in the ODS.  Checking that the
signature of a custom builder conflicts with that of a default builder to
prevent emission would require teaching ODG to differentiate between types and
(optional) argument names in the generated C++ code.  If this flag ends up
being used a lot, we should consider adding traits that inject specific code
into the default builder.

PiperOrigin-RevId: 256640069

mlir/include/mlir/IR/OpBase.td

@@ -1082,8 +1082,9 @@ class Op<Dialect dialect, string mnemonic, list<OpTrait> props = []> {
   // Define the hooks used for building, parsing, printing, verification.
 
   // Custom builder.
-  // In addtion to the custom builder provided here, two default builders
-  // are generated, with the following signatures:
+  // In addition to the custom builder provided here, and unless
+  // skipDefaultBuilders is set, two default builders are generated, with the
+  // following signatures:
   //
   // ```c++
   // static void build(Builder *, OperationState *tblgen_state,
@@ -1101,6 +1102,10 @@ class Op<Dialect dialect, string mnemonic, list<OpTrait> props = []> {
   // ```
   list<OpBuilder> builders = ?;
 
+  // Avoid generating default build functions.  Custom builders must be
+  // provided.
+  bit skipDefaultBuilders = 0;
+
   // Custom parser.
   code parser = ?;
 

mlir/include/mlir/TableGen/Operator.h

@@ -74,6 +74,9 @@ public:
   // Returns true if this op has variadic operands or results.
   bool isVariadic() const;
 
+  // Returns true if default builders should not be generated.
+  bool skipDefaultBuilders() const;
+
   // Op result iterators.
   value_iterator result_begin();
   value_iterator result_end();

mlir/lib/TableGen/Operator.cpp

@@ -93,6 +93,10 @@ bool tblgen::Operator::isVariadic() const {
   return getNumVariadicOperands() != 0 || getNumVariadicResults() != 0;
 }
 
+bool tblgen::Operator::skipDefaultBuilders() const {
+  return def.getValueAsBit("skipDefaultBuilders");
+}
+
 auto tblgen::Operator::result_begin() -> value_iterator {
   return results.begin();
 }

mlir/test/mlir-tblgen/op-decl.td

@@ -99,6 +99,19 @@ def NS_DOp : NS_Op<"op_with_two_operands", []> {
 // CHECK-LABEL: NS::DOp declarations
 // CHECK: OpTrait::NOperands<2>::Impl
 
+// Check that default builders can be suppressed.
+// ---
+
+def NS_SkipDefaultBuildersOp : NS_Op<"skip_default_builders", []> {
+  let skipDefaultBuilders = 1;
+  let builders = [OpBuilder<"Value *val">];
+}
+
+// CHECK-LABEL: NS::SkipDefaultBuildersOp declarations
+// CHECK:     class SkipDefaultBuildersOp
+// CHECK-NOT:   static void build(Builder
+// CHECK:       static void build(Value
+
 // Check leading underscore in op name
 // ---
 

mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp

@@ -884,6 +884,13 @@ void OpEmitter::genBuilder() {
           method.body() << body;
       }
     }
+    if (op.skipDefaultBuilders()) {
+      if (!listInit || listInit->empty())
+        PrintFatalError(
+            op.getLoc(),
+            "default builders are skipped and no custom builders provided");
+      return;
+    }
   }
 
   int numResults = op.getNumResults();