Code Generation Utilties

Contents

• Code Generation Utilties
  • Introduction
  • Structures

Introduction

Numba uses llvmpy for code generation. The numba/cgutils.py file provides utilities to simplify many common tasks.

Structures

The numba.cgutils.Structure class is used like the ctypes.Structure for manuipluting structures. The _fields class attribute declares a list of (name, type) pairs for each field of the structure.

For example, The complex number structures are defined as:

from numba import types, cgutils

class Complex64(cgutils.Structure):
    _fields = [('real', types.float32),
               ('imag', types.float32)]


class Complex128(cgutils.Structure):
    _fields = [('real', types.float64),
               ('imag', types.float64)]

The constructor of Structure requires the codegen context and llvm builder. Optionally, user can provide the value keyword argument to initialize the structure with a LLVM value of compatible type. Structures are allocated using llvm.Builder.alloca. (The alloca operation is automatically placed as the first block of the current function.) User can provide the ref keyword argument to specify a custom storage space. It should contain a LLVM pointer of compatible type. To get the pointer to the allocated space, use Structure._getpointer. To get a copy of the structure as a value, use Structure._getvalue. The two functions returns a LLVM value (instance of llvm.core.Value).

Each field is a load/store property of the Structure instance. Accessing the real field of Complex64, for example, looks like:

c = Complex64(context, builder)
c.real = llvm.core.Constant.real(lc.Type.float32, 1.23)
two_times_real = builder.add(c.real, c.real)