CompletionModelCodegen.py

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"""Code generator for Code Completion Model Inference.
 
Tool runs on the Decision Forest model defined in {model} directory.
It generates two files: {output_dir}/{filename}.h and {output_dir}/{filename}.cpp
The generated files defines the Example class named {cpp_class} having all the features as class members.
The generated runtime provides an `Evaluate` function which can be used to score a code completion candidate.
"""
 
import argparse
import json
import struct
 
 
class CppClass:
    """Holds class name and names of the enclosing namespaces."""
 
    def __init__(self, cpp_class):
        ns_and_class = cpp_class.split("::")
        self.ns = [ns for ns in ns_and_class[0:-1] if len(ns) > 0]
        self.name = ns_and_class[-1]
        if len(self.name) == 0:
            raise ValueError("Empty class name.")
 
    def ns_begin(self):
        """Returns snippet for opening namespace declarations."""
        open_ns = ["namespace %s {" % ns for ns in self.ns]
        return "\n".join(open_ns)
 
    def ns_end(self):
        """Returns snippet for closing namespace declarations."""
        close_ns = ["} // namespace %s" % ns for ns in reversed(self.ns)]
        return "\n".join(close_ns)
 
 
def header_guard(filename):
    """Returns the header guard for the generated header."""
    return "GENERATED_DECISION_FOREST_MODEL_%s_H" % filename.upper()
 
 
def boost_node(n, label, next_label):
    """Returns code snippet for a leaf/boost node."""
    return "%s: return %sf;" % (label, n["score"])
 
 
def if_greater_node(n, label, next_label):
    """Returns code snippet for a if_greater node.
    Jumps to true_label if the Example feature (NUMBER) is greater than the threshold.
    Comparing integers is much faster than comparing floats. Assuming floating points
    are represented as IEEE 754, it order-encodes the floats to integers before comparing them.
    Control falls through if condition is evaluated to false."""
    threshold = n["threshold"]
    return "%s: if (E.get%s() >= %s /*%s*/) goto %s;" % (
        label,
        n["feature"],
        order_encode(threshold),
        threshold,
        next_label,
    )
 
 
def if_member_node(n, label, next_label):
    """Returns code snippet for a if_member node.
    Jumps to true_label if the Example feature (ENUM) is present in the set of enum values
    described in the node.
    Control falls through if condition is evaluated to false."""
    members = "|".join(
        ["BIT(%s_type::%s)" % (n["feature"], member) for member in n["set"]]
    )
    return "%s: if (E.get%s() & (%s)) goto %s;" % (
        label,
        n["feature"],
        members,
        next_label,
    )
 
 
def node(n, label, next_label):
    """Returns code snippet for the node."""
    return {
        "boost": boost_node,
        "if_greater": if_greater_node,
        "if_member": if_member_node,
    }[n["operation"]](n, label, next_label)
 
 
def tree(t, tree_num, node_num):
    """Returns code for inferencing a Decision Tree.
    Also returns the size of the decision tree.
 
    A tree starts with its label `t{tree#}`.
    A node of the tree starts with label `t{tree#}_n{node#}`.
 
    The tree contains two types of node: Conditional node and Leaf node.
    -   Conditional node evaluates a condition. If true, it jumps to the true node/child.
        Code is generated using pre-order traversal of the tree considering
        false node as the first child. Therefore the false node is always the
        immediately next label.
    -   Leaf node adds the value to the score and jumps to the next tree.
    """
    label = "t%d_n%d" % (tree_num, node_num)
    code = []
 
    if t["operation"] == "boost":
        code.append(node(t, label=label, next_label="t%d" % (tree_num + 1)))
        return code, 1
 
    false_code, false_size = tree(t["else"], tree_num=tree_num, node_num=node_num + 1)
 
    true_node_num = node_num + false_size + 1
    true_label = "t%d_n%d" % (tree_num, true_node_num)
 
    true_code, true_size = tree(t["then"], tree_num=tree_num, node_num=true_node_num)
 
    code.append(node(t, label=label, next_label=true_label))
 
    return code + false_code + true_code, 1 + false_size + true_size
 
 
def gen_header_code(features_json, cpp_class, filename):
    """Returns code for header declaring the inference runtime.
 
    Declares the Example class named {cpp_class} inside relevant namespaces.
    The Example class contains all the features as class members. This
    class can be used to represent a code completion candidate.
    Provides `float Evaluate()` function which can be used to score the Example.
    """
    setters = []
    getters = []
    for f in features_json:
        feature = f["name"]
 
        if f["kind"] == "NUMBER":
            # Floats are order-encoded to integers for faster comparison.
            setters.append(
                "void set%s(float V) { %s = OrderEncode(V); }" % (feature, feature)
            )
        elif f["kind"] == "ENUM":
            setters.append(
                "void set%s(unsigned V) { %s = 1LL << V; }" % (feature, feature)
            )
        else:
            raise ValueError("Unhandled feature type.", f["kind"])
 
    # Class members represent all the features of the Example.
    class_members = [
        "uint%d_t %s = 0;" % (64 if f["kind"] == "ENUM" else 32, f["name"])
        for f in features_json
    ]
    getters = [
        "LLVM_ATTRIBUTE_ALWAYS_INLINE uint%d_t get%s() const { return %s; }"
        % (64 if f["kind"] == "ENUM" else 32, f["name"], f["name"])
        for f in features_json
    ]
    nline = "\n  "
    guard = header_guard(filename)
    return """#ifndef %s
#define %s
#include <cstdint>
#include "llvm/Support/Compiler.h"
 
%s
class %s {
public:
  // Setters.
  %s
 
  // Getters.
  %s
 
private:
  %s
 
  // Produces an integer that sorts in the same order as F.
  // That is: a < b <==> orderEncode(a) < orderEncode(b).
  static uint32_t OrderEncode(float F);
};
 
float Evaluate(const %s&);
%s
#endif // %s
""" % (
        guard,
        guard,
        cpp_class.ns_begin(),
        cpp_class.name,
        nline.join(setters),
        nline.join(getters),
        nline.join(class_members),
        cpp_class.name,
        cpp_class.ns_end(),
        guard,
    )
 
 
def order_encode(v):
    i = struct.unpack("<I", struct.pack("<f", v))[0]
    TopBit = 1 << 31
    # IEEE 754 floats compare like sign-magnitude integers.
    if i & TopBit:  # Negative float
        return (1 << 32) - i  # low half of integers, order reversed.
    return TopBit + i  # top half of integers
 
 
def evaluate_func(forest_json, cpp_class):
    """Generates evaluation functions for each tree and combines them in
    `float Evaluate(const {Example}&)` function. This function can be
    used to score an Example."""
 
    code = ""
 
    # Generate evaluation function of each tree.
    code += "namespace {\n"
    tree_num = 0
    for tree_json in forest_json:
        code += "LLVM_ATTRIBUTE_NOINLINE float EvaluateTree%d(const %s& E) {\n" % (
            tree_num,
            cpp_class.name,
        )
        code += (
            "  " + "\n  ".join(tree(tree_json, tree_num=tree_num, node_num=0)[0]) + "\n"
        )
        code += "}\n\n"
        tree_num += 1
    code += "} // namespace\n\n"
 
    # Combine the scores of all trees in the final function.
    # MSAN will timeout if these functions are inlined.
    code += "float Evaluate(const %s& E) {\n" % cpp_class.name
    code += "  float Score = 0;\n"
    for tree_num in range(len(forest_json)):
        code += "  Score += EvaluateTree%d(E);\n" % tree_num
    code += "  return Score;\n"
    code += "}\n"
 
    return code
 
 
def gen_cpp_code(forest_json, features_json, filename, cpp_class):
    """Generates code for the .cpp file."""
    # Headers
    # Required by OrderEncode(float F).
    angled_include = ["#include <%s>" % h for h in ["cstring", "limits"]]
 
    # Include generated header.
    qouted_headers = {filename + ".h", "llvm/ADT/bit.h"}
    # Headers required by ENUM features used by the model.
    qouted_headers |= {f["header"] for f in features_json if f["kind"] == "ENUM"}
    quoted_include = ['#include "%s"' % h for h in sorted(qouted_headers)]
 
    # using-decl for ENUM features.
    using_decls = "\n".join(
        "using %s_type = %s;" % (feature["name"], feature["type"])
        for feature in features_json
        if feature["kind"] == "ENUM"
    )
    nl = "\n"
    return """%s
 
%s
 
#define BIT(X) (1LL << X)
 
%s
 
%s
 
uint32_t %s::OrderEncode(float F) {
  static_assert(std::numeric_limits<float>::is_iec559, "");
  constexpr uint32_t TopBit = ~(~uint32_t{0} >> 1);
 
  // Get the bits of the float. Endianness is the same as for integers.
  uint32_t U = llvm::bit_cast<uint32_t>(F);
  std::memcpy(&U, &F, sizeof(U));
  // IEEE 754 floats compare like sign-magnitude integers.
  if (U & TopBit)    // Negative float.
    return 0 - U;    // Map onto the low half of integers, order reversed.
  return U + TopBit; // Positive floats map onto the high half of integers.
}
 
%s
%s
""" % (
        nl.join(angled_include),
        nl.join(quoted_include),
        cpp_class.ns_begin(),
        using_decls,
        cpp_class.name,
        evaluate_func(forest_json, cpp_class),
        cpp_class.ns_end(),
    )
 
 
def main():
    parser = argparse.ArgumentParser("DecisionForestCodegen")
    parser.add_argument("--filename", help="output file name.")
    parser.add_argument("--output_dir", help="output directory.")
    parser.add_argument("--model", help="path to model directory.")
    parser.add_argument(
        "--cpp_class",
        help="The name of the class (which may be a namespace-qualified) created in generated header.",
    )
    ns = parser.parse_args()
 
    output_dir = ns.output_dir
    filename = ns.filename
    header_file = "%s/%s.h" % (output_dir, filename)
    cpp_file = "%s/%s.cpp" % (output_dir, filename)
    cpp_class = CppClass(cpp_class=ns.cpp_class)
 
    model_file = "%s/forest.json" % ns.model
    features_file = "%s/features.json" % ns.model
 
    with open(features_file) as f:
        features_json = json.load(f)
 
    with open(model_file) as m:
        forest_json = json.load(m)
 
    with open(cpp_file, "w+t") as output_cc:
        output_cc.write(
            gen_cpp_code(
                forest_json=forest_json,
                features_json=features_json,
                filename=filename,
                cpp_class=cpp_class,
            )
        )
 
    with open(header_file, "w+t") as output_h:
        output_h.write(
            gen_header_code(
                features_json=features_json, cpp_class=cpp_class, filename=filename
            )
        )
 
 
if __name__ == "__main__":
    main()