simooo21/vb6-to-cs-training-pipeline

VB6 → C# Code Translation LLM

A complete training pipeline to fine-tune a code LLM for translating VB6 to C# using SFT + GRPO for maximum quality.

Architecture

Qwen2.5-Coder-7B-Instruct
      ↓
   SFT (360 examples, 3 epochs)
      ↓
  simooo21/vb6-to-cs-qwen2.5-coder-7b-sft
      ↓
   GRPO (reward: syntax + format + length, 2 epochs)
      ↓
  simooo21/vb6-to-cs-qwen2.5-coder-7b-grpo

Dataset

• Source: simooo21/vb6-to-csharp-translation
• Size: 360 train, 40 validation
• Format: Conversational messages ([{"role": "user"}, {"role": "assistant"}])
• Coverage: 41 VB6 → C# translation patterns across 40 categories:

Category	Examples	Key Mappings
variables	Dim → type declaration	Dim x As Integer → int x;
control_flow	If/Select Case → if/switch	Select Case → switch
loops	For/Do/For Each → for/while/foreach	For Each → foreach
functions	Sub/Function → methods	ByRef → ref, Optional → default params
arrays	1-based → 0-based arrays	Dim arr(1 To 5) → int[] arr = new int[5]
strings	VB6 string funcs → C# methods	UCase/Trim/Len → ToUpper/Trim/Length
file_io	Open/Close → StreamReader/Writer	FreeFile → using statement
error_handling	On Error → try/catch	On Error GoTo → try { } catch
gui_events	Event subs → event handlers	cmd_Click() → cmd_Click(object, EventArgs)
gui_controls	VB6 controls → WinForms	ComboBox.AddItem → Items.Add
form_designer	.frm code → C# InitializeComponent	VB6 form layout → C# programmatic UI
database	ADO → SqlClient	ADODB.Connection → SqlConnection
api_calls	Declare → DllImport	Declare Function → [DllImport]
classes	VB6 class → C# class	Property Get/Let → C# properties
structs	Type → struct	Public Type → public struct
collections	Collection → Dictionary	Scripting.Dictionary → Dictionary<K,V>
regex	Like → Regex	Like "[A-Z]###" → Regex.IsMatch
enums	VB6 Enum → C# enum	Direct mapping with values
events	RaiseEvent → event invocation	RaiseEvent → ?.Invoke
interfaces	Implements → : interface	Implements INotifyPropertyChanged → : INotifyPropertyChanged
modules	Module-level → static class	Public Const → public const
dialogs	MsgBox/InputBox → MessageBox	vbModal → ShowDialog()
async	DoEvents → async/await	DoEvents → Application.DoEvents() / await
datetime	Date functions → DateTime	Now/DateAdd/DateDiff → DateTime.Now/AddDays
math	Rnd → Random	Rnd → Random.Next
formatting	Format → ToString	FormatCurrency → .ToString("C2")
conversions	CStr/CInt → Convert	CStr/CInt/CDate → Convert.ToString/Int32/DateTime
type_checks	IsNumeric → TryParse	IsNumeric → int.TryParse
operators	IIf → ternary	IIf(condition, a, b) → condition ? a : b
networking	Winsock → TcpClient	Winsock → TcpClient/NetworkStream
com_interop	CreateObject → Activator	CreateObject("Word.Application") → Activator.CreateInstance
printing	Printer → PrintDocument	Printer.Print → e.Graphics.DrawString
graphics	LoadPicture → Image.FromFile	Direct mapping
system	SendKeys → SendKeys.SendWait	Direct mapping
application	App.Path → Assembly	App.Path → Application.ExecutablePath
entry_point	Sub Main → static void Main	With [STAThread] attribute
null_checks	IsNull/Nothing → null/DBNull	Is Nothing → == null
access_modifiers	Friend → internal	Friend → internal

Training Recipes

Phase 1: SFT (Supervised Fine-Tuning)

Base model: Qwen/Qwen2.5-Coder-7B-Instruct

python train_sft.py

Hyperparameters (from OpenCodeInstruct):

Parameter	Value	Rationale
lr	5e-6	Low LR for stable convergence on small dataset
epochs	3	Full coverage of 360 examples
batch	1 × 8 accum	Effective batch 8 per GPU
seq_len	1024	All examples fit (max 570 tokens)
warmup	50 steps	Smooth start
scheduler	cosine (default)	Proven for code tasks

Phase 2: GRPO (Reinforcement Learning)

Base model: simooo21/vb6-to-cs-qwen2.5-coder-7b-sft

python train_grpo.py

Hyperparameters (from DRIVE / DeepSeekMath):

Parameter	Value	Rationale
lr	1e-6	Very low for RL stability
epochs	2	Don't overfit on small data
num_generations	8	Group size per prompt
max_completion	2048	Long enough for code
rewards	syntax + format + length	Multi-objective optimization

Reward Functions

1. syntax_reward (0-1): Checks C# syntax patterns

   • Access modifiers (+0.2)
   • Balanced braces (+0.2)
   • Semicolons (+0.1)
   • Type declarations (+0.2)
   • Using/namespace (+0.1)
   • Class/struct (+0.1)
   • Balanced brackets (+0.1)

2. format_reward (0-1): Checks for ```csharp code blocks

3. length_reward (0-1): Rewards reasonable code length (3-100 lines)

Hardware Requirements

• SFT: 1× A10G (24GB) or better. ~2-3 hours.
• GRPO: 1× A10G or A100. ~3-4 hours.
• For multi-GPU: use accelerate launch

Evaluation

python evaluate_model.py --model simooo21/vb6-to-cs-qwen2.5-coder-7b-grpo

Reports:

• Exact match rate
• Code block extraction rate
• Mean syntax score (0-1)
• Mean Levenshtein distance
• Per-category breakdown

Why SFT + GRPO?

Per the literature review:

1. SFT alone gets you far with high-quality data (OpenCodeInstruct showed 5M samples beats small-model RL)
2. GRPO with verifiable rewards is the new SOTA for code generation (DRIVE: +58.3% on Codeforces)
3. Two-stage pipeline is proven: SFT first for imitation learning, then RL for exploration and reward optimization
4. Multi-objective rewards (syntax + format + length) prevent reward hacking and produce balanced outputs

References

1. OpenCodeInstruct (2025) - lr=5e-6, 3 epochs, batch=2048 for SFT. Paper
2. DRIVE (2025) - Two-stage GRPO with verifiable rewards. Paper
3. DeepSeekMath (2024) - GRPO algorithm foundation. Paper
4. StepCoder (2024) - Compiler feedback for code RL. Paper
5. Lost in Translation (2023) - Cross-language code translation challenges. Paper