[mlir][ODS] Fix `VariadicRegion` code generation for `NoTerminator` Ops

[vinograd47]

Summary

The issue was introduced in D98468.

The {0}Regions is an array of std::unique_ptr<Region> objects,
so it should be processed accordingly.

[mehdi_amini]

Is it possible to make it exercised in tree? Maybe in the TestDialect?

[mehdi_amini]

(if this unblocks you, feel free to land it and send me a test afterward)

[vinograd47]

Added a test for the issue

mlir/test/IR/region.mlir

 
 // -----
 
 // Region with single block and not terminator.
 // CHECK: unregistered_without_terminator
 "test.unregistered_without_terminator"() ( {
   ^bb0:  // no predecessors
 }) : () -> ()
+
+// -----
+
+// CHECK: test.single_no_terminator_op
+"test.single_no_terminator_op"() (
+  {
+    func @foo1() { return }
+    func @foo2() { return }
+  }
+) : () -> ()
+
+// CHECK: test.variadic_no_terminator_op
+"test.variadic_no_terminator_op"() (
+  {
+    func @foo1() { return }
+  },
+  {
+    func @foo2() { return }
+  }
+) : () -> ()

mlir/test/lib/Dialect/Test/TestOps.td

def TwoRegionOp : TEST_Op<"two_region_op", []> {
   let regions = (region AnyRegion, AnyRegion);
 }
 
 def SizedRegionOp : TEST_Op<"sized_region_op", []> {
   let regions = (region SizedRegion<2>:$my_region, SizedRegion<1>);
 }
 
 //===----------------------------------------------------------------------===//
+// NoTerminator Operation
+//===----------------------------------------------------------------------===//
+
+def SingleNoTerminatorOp : TEST_Op<"single_no_terminator_op", GraphRegionNoTerminator.traits> {
+  let regions = (region SizedRegion<1>:$my_region);
+
+  let assemblyFormat = "attr-dict `:` $my_region";
+}
+
+def VariadicNoTerminatorOp : TEST_Op<"variadic_no_terminator_op", GraphRegionNoTerminator.traits> {
+  let regions = (region VariadicRegion<SizedRegion<1>>:$my_regions);
+
+  let assemblyFormat = "attr-dict `:` $my_regions";
+}
+
+//===----------------------------------------------------------------------===//
 // Test Call Interfaces
 //===----------------------------------------------------------------------===//
 
 def ConversionCallOp : TEST_Op<"conversion_call_op",
     [CallOpInterface]> {
   let arguments = (ins Variadic<AnyType>:$inputs, SymbolRefAttr:$callee);
   let results = (outs Variadic<AnyType>);
 

mlir/tools/mlir-tblgen/OpFormatGen.cpp

for (auto &region : {0}Regions)
     ensureTerminator(*region, parser.getBuilder(), result.location);
 )";
 
 /// The code snippet used to ensure a list of regions have a block.
 ///
 /// {0}: The name of the region list.
 const char *regionListEnsureSingleBlockParserCode = R"(
   for (auto &region : {0}Regions)
-    if (region.empty()) *{0}Region.emplaceBlock();
+    if (region->empty()) region->emplaceBlock();
 )";
 
 /// The code snippet used to generate a parser call for an optional region.
 ///
 /// {0}: The name of the region.
 const char *optionalRegionParserCode = R"(
   {
      auto parseResult = parser.parseOptionalRegion(*{0}Region);