add ptq data-free method (#1026)

* add ptq data-free method

paddleslim/auto_compression/utils/fake_ptq.py

+import paddle
+from paddle.fluid.framework import IrGraph
+from paddle.fluid import core
+from paddle.fluid.contrib.slim.quantization import QuantizationTransformPass, AddQuantDequantPass, QuantizationFreezePass
+
+
+def post_quant_fake(executor,
+                    model_dir,
+                    model_filename=None,
+                    params_filename=None,
+                    save_model_path=None,
+                    quantizable_op_type=["conv2d", "depthwise_conv2d", "mul"],
+                    is_full_quantize=False,
+                    activation_bits=8,
+                    weight_bits=8):
+    """
+    Utilizing post training quantization methon to quantize the FP32 model,
+    and it not uses calibrate data and the fake model cannot be used in practice.
+    Usage:
+        paddle.enable_static()
+        place = paddle.CPUPlace()
+        exe = paddle.static.Executor(place)
+        post_quant_fake(executor=exe, 
+            model_dir='./inference_model/MobileNet/',
+            model_filename='model',
+            params_filename='params',
+            save_model_path='fake_quant')
+    """
+    activation_quantize_type = 'range_abs_max'
+    weight_quantize_type = 'channel_wise_abs_max'
+    _dynamic_quantize_op_type = ['lstm']
+    _weight_supported_quantizable_op_type = QuantizationTransformPass._supported_quantizable_op_type
+    _act_supported_quantizable_op_type = AddQuantDequantPass._supported_quantizable_op_type
+    _support_quantize_op_type = list(
+        set(_weight_supported_quantizable_op_type +
+            _act_supported_quantizable_op_type + _dynamic_quantize_op_type))
+    _place = executor.place
+    _scope = paddle.static.global_scope()
+    if is_full_quantize:
+        _quantizable_op_type = _support_quantize_op_type
+    else:
+        _quantizable_op_type = quantizable_op_type
+        for op_type in _quantizable_op_type:
+            assert op_type in _support_quantize_op_type, \
+                op_type + " is not supported for quantization."
+
+    _program, _feed_list, _fetch_list = paddle.fluid.io.load_inference_model(
+        model_dir,
+        executor,
+        model_filename=model_filename,
+        params_filename=params_filename)
+
+    graph = IrGraph(core.Graph(_program.desc), for_test=True)
+
+    # use QuantizationTransformPass to insert fake_quant/fake_dequantize op
+    major_quantizable_op_types = []
+    for op_type in _weight_supported_quantizable_op_type:
+        if op_type in _quantizable_op_type:
+            major_quantizable_op_types.append(op_type)
+    transform_pass = QuantizationTransformPass(
+        scope=_scope,
+        place=_place,
+        weight_bits=weight_bits,
+        activation_bits=activation_bits,
+        activation_quantize_type=activation_quantize_type,
+        weight_quantize_type=weight_quantize_type,
+        quantizable_op_type=major_quantizable_op_types)
+
+    for sub_graph in graph.all_sub_graphs():
+        # Insert fake_quant/fake_dequantize op must in test graph, so
+        # set per graph's _for_test is True.
+        sub_graph._for_test = True
+        transform_pass.apply(sub_graph)
+
+    # use AddQuantDequantPass to insert fake_quant_dequant op
+    minor_quantizable_op_types = []
+    for op_type in _act_supported_quantizable_op_type:
+        if op_type in _quantizable_op_type:
+            minor_quantizable_op_types.append(op_type)
+    add_quant_dequant_pass = AddQuantDequantPass(
+        scope=_scope,
+        place=_place,
+        quantizable_op_type=minor_quantizable_op_types)
+
+    for sub_graph in graph.all_sub_graphs():
+        sub_graph._for_test = True
+        add_quant_dequant_pass.apply(sub_graph)
+
+    # apply QuantizationFreezePass, and obtain the final quant model
+    freeze_pass = QuantizationFreezePass(
+        scope=_scope,
+        place=_place,
+        weight_bits=weight_bits,
+        activation_bits=activation_bits,
+        weight_quantize_type=weight_quantize_type,
+        quantizable_op_type=major_quantizable_op_types)
+
+    for sub_graph in graph.all_sub_graphs():
+        sub_graph._for_test = True
+        freeze_pass.apply(sub_graph)
+
+    _program = graph.to_program()
+
+    paddle.fluid.io.save_inference_model(
+        dirname=save_model_path,
+        model_filename=model_filename,
+        params_filename=params_filename,
+        feeded_var_names=_feed_list,
+        target_vars=_fetch_list,
+        executor=executor,
+        main_program=_program)
+    print("The quantized model is saved in: " + save_model_path)