[mlir][tblgen] Fix region and successor references in custom directives

Previously, references to regions and successors were incorrectly disallowed outside the top-level assembly form. This change enables the use of bound regions and successors as variables in custom directives.

Author: xlauko

mlir/test/mlir-tblgen/op-format-spec.td

@@ -49,6 +49,19 @@ def DirectiveCustomValidD : TestFormat_Op<[{
 def DirectiveCustomValidE : TestFormat_Op<[{
   custom<MyDirective>(prop-dict) attr-dict
 }]>, Arguments<(ins UnitAttr:$flag)>;
+def DirectiveCustomValidF : TestFormat_Op<[{
+  $operand custom<MyDirective>(ref($operand)) attr-dict
+}]>, Arguments<(ins Optional<I64>:$operand)>;
+def DirectiveCustomValidG : TestFormat_Op<[{
+  $body custom<MyDirective>(ref($body)) attr-dict
+}]> {
+  let regions = (region AnyRegion:$body);
+}
+def DirectiveCustomValidH : TestFormat_Op<[{
+  $successor custom<MyDirective>(ref($successor)) attr-dict
+}]> {
+  let successors = (successor AnySuccessor:$successor);
+}
 
 //===----------------------------------------------------------------------===//
 // functional-type

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

@@ -109,3 +109,24 @@ def OptionalGroupC : TestFormat_Op<[{
 def OptionalGroupD : TestFormat_Op<[{
   (custom<Custom>($a, $b)^)? attr-dict
 }], [AttrSizedOperandSegments]>, Arguments<(ins Optional<I64>:$a, Optional<I64>:$b)>;
+
+
+// CHECK-LABEL: RegionRef::parse
+// CHECK:   auto odsResult = parseCustom(parser, *bodyRegion);
+// CHECK-LABEL: RegionRef::print
+// CHECK:   printCustom(_odsPrinter, *this, getBody());
+def RegionRef : TestFormat_Op<[{
+  $body custom<Custom>(ref($body)) attr-dict
+}]> {
+  let regions = (region AnyRegion:$body);
+}
+
+// CHECK-LABEL: SuccessorRef::parse
+// CHECK:   auto odsResult = parseCustom(parser, successorSuccessor);
+// CHECK-LABEL: SuccessorRef::print
+// CHECK:   printCustom(_odsPrinter, *this, getSuccessor());
+def SuccessorRef : TestFormat_Op<[{
+  $successor custom<Custom>(ref($successor)) attr-dict
+}]> {
+  let successors = (successor AnySuccessor:$successor);
+}

mlir/tools/mlir-tblgen/OpFormatGen.cpp

@@ -3376,11 +3376,13 @@ OpFormatParser::parseVariableImpl(SMLoc loc, StringRef name, Context ctx) {
     if (ctx == TopLevelContext || ctx == CustomDirectiveContext) {
       if (hasAllRegions || !seenRegions.insert(region).second)
         return emitError(loc, "region '" + name + "' is already bound");
-    } else if (ctx == RefDirectiveContext && !seenRegions.count(region)) {
-      return emitError(loc, "region '" + name +
-                                "' must be bound before it is referenced");
+    } else if (ctx == RefDirectiveContext) {
+      if (!seenRegions.count(region))
+        return emitError(loc, "region '" + name +
+                                  "' must be bound before it is referenced");
     } else {
-      return emitError(loc, "regions can only be used at the top level");
+      return emitError(loc, "regions can only be used at the top level "
+                            "or in a ref directive");
     }
     return create<RegionVariable>(region);
   }
@@ -3396,11 +3398,13 @@ OpFormatParser::parseVariableImpl(SMLoc loc, StringRef name, Context ctx) {
     if (ctx == TopLevelContext || ctx == CustomDirectiveContext) {
       if (hasAllSuccessors || !seenSuccessors.insert(successor).second)
         return emitError(loc, "successor '" + name + "' is already bound");
-    } else if (ctx == RefDirectiveContext && !seenSuccessors.count(successor)) {
-      return emitError(loc, "successor '" + name +
-                                "' must be bound before it is referenced");
+    } else if (ctx == RefDirectiveContext) {
+      if (!seenSuccessors.count(successor))
+        return emitError(loc, "successor '" + name +
+                                  "' must be bound before it is referenced");
     } else {
-      return emitError(loc, "successors can only be used at the top level");
+      return emitError(loc, "successors can only be used at the top level "
+                            "or in a ref directive");
     }
 
     return create<SuccessorVariable>(successor);