[mlir] VectorToSCF bug in setAllocAtFunctionEntry fixed.

[limo1996]

Summary

The function makes too strong assumption regarding parent FuncOp
which gets broken when FuncOp is first lowered to llvm function.
In this fix we generalize the assumption to allocation scope and
add assertion to produce user friendly message in case our assumption
is broken.

mlir/lib/Conversion/VectorToSCF/VectorToSCF.cpp

Value NDTransferOpHelper<ConcreteOp>::emitInBoundsCondition(
   return inBoundsCondition;
 }
 
 // TODO: Parallelism and threadlocal considerations.
 static Value setAllocAtFunctionEntry(MemRefType memRefMinorVectorType,
                                      Operation *op) {
   auto &b = ScopedContext::getBuilderRef();
   OpBuilder::InsertionGuard guard(b);
-  b.setInsertionPointToStart(&op->getParentOfType<FuncOp>().front());
+  Operation *scope =
+      op->getParentWithTrait<OpTrait::AutomaticAllocationScope>();
+  assert(scope && "Expected op to be inside automatic allocation scope");
+  b.setInsertionPointToStart(&scope->getRegion(0).front());
   Value res =
       std_alloca(memRefMinorVectorType, ValueRange{}, b.getI64IntegerAttr(128));
   return res;
 }
 
 template <>
 LogicalResult NDTransferOpHelper<TransferReadOp>::doReplace() {
   Value alloc, result;