[mlir] Assume terminators in nested regions are always legal in FuncBufferizePass

[Hardcode84]

Summary

Previously, any terminator without ReturnLike and BranchOpInterface traits (e.g. scf.condition) were causing pass to fail.

[silvas]

Thanks!

mlir/lib/Dialect/StandardOps/Transforms/FuncConversions.cpp

if (!op->mightHaveTrait<OpTrait::IsTerminator>())
     return true;
 
   // If it is not the last operation in the block, also ignore it. We do
   // this to handle unknown operations, as well.
   Block *block = op->getBlock();
   if (!block || &block->back() != op)
     return true;
 
+  // We don't want to handle terminators in nested regions, assume they are
+  // always legal.
+  if (!isa_and_nonnull<FuncOp>(op->getParentOp()))
+    return true;
+
   return false;
 }

mlir/test/Dialect/Standard/func-bufferize.mlir

func @unable_to_update_terminator(%arg0: tensor<f32>) -> tensor<f32> {
     %0 = constant true
     cond_br %0, ^bb1(%arg0: tensor<f32>), ^bb2(%arg0: tensor<f32>)
   ^bb1(%bbarg0: tensor<f32>):
     // expected-error @+1 {{failed to legalize operation 'test.terminator'}}
     "test.terminator"() : () -> ()
   ^bb2(%bbarg1: tensor<f32>):
     return %bbarg1 : tensor<f32>
 }
+
+// -----
+
+// There was a bug in func-bufferize pass which caused terminators without
+// ReturnLike and BranchOpInterface traits (e.g. scf.condition) to always
+// fail to legalize even if bufferization doesn't needed.
+// Check the pass succedeed.
+// CHECK: bufferize_while
+// CHECK: scf.while
+// CHECK: scf.condition
+func @bufferize_while(%arg0: i64, %arg1: i64) -> i64 {
+  %c2_i64 = constant 2 : i64
+  %0:2 = scf.while (%arg2 = %arg0) : (i64) -> (i64, i64) {
+    %1 = cmpi slt, %arg2, %arg1 : i64
+    scf.condition(%1) %arg2, %arg2 : i64, i64
+  } do {
+  ^bb0(%arg2: i64, %arg3: i64):
+    %1 = muli %arg3, %c2_i64 : i64
+    scf.yield %1 : i64
+  }
+  return %0#1 : i64
+}