Example for calling functions via ctypes (Andrew Straw)

git-svn-id: http://llvm-py.googlecode.com/svn/trunk@80 8d1e9007-1d4e-0410-b67e-1979fd6579aa

test/call-jit-ctypes.py

@@ -0,0 +1,64 @@
+#!/usr/bin/env python
+
+from llvm.core import Module,Type,Builder,ModuleProvider
+from llvm.ee import ExecutionEngine
+import llvm.core
+import ctypes
+
+def test_jit_ctypes():
+
+    # This example demonstrates calling an LLVM defined function using
+    # ctypes. It illustrates the common C pattern of having an output
+    # variable in the argument list to the function. The function also
+    # returns an error code upon exit.
+
+    # setup llvm types
+    ty_errcode = Type.int()
+    ty_float = Type.float()
+    ty_ptr_float = Type.pointer(Type.float())
+    ty_func = Type.function(ty_errcode, [ty_float, ty_float, ty_ptr_float])
+
+    # setup ctypes types
+    ct_errcode = ctypes.c_int
+    ct_float = ctypes.c_float
+    ct_ptr_float = ctypes.POINTER(ct_float)
+    ct_argtypes = [ct_float, ct_float, ct_ptr_float]
+
+    # generate the function using LLVM
+    my_module = Module.new('my_module')
+
+    mult = my_module.add_function(ty_func, "mult")
+    mult.args[0].name = "a"
+    mult.args[1].name = "b"
+    mult.args[2].name = "out"
+    mult.args[2].add_attribute(llvm.core.ATTR_NO_CAPTURE) # add nocapture to output arg
+    mult.does_not_throw = True # add nounwind attribute to function
+
+    bb = mult.append_basic_block("entry")
+    builder = Builder.new(bb)
+    tmp = builder.mul( mult.args[0], mult.args[1] )
+    builder.store( tmp, mult.args[2] )
+    builder.ret(llvm.core.Constant.int(ty_errcode, 0))
+
+    if 0:
+        # print the created module
+        print my_module
+
+    # compile the function
+    mp = ModuleProvider.new(my_module)
+    ee = ExecutionEngine.new(mp)
+
+    # let ctypes know about the function
+    func_ptr_int = ee.get_pointer_to_function( mult )
+    FUNC_TYPE = ctypes.CFUNCTYPE(ct_errcode, *ct_argtypes)
+    py_mult = FUNC_TYPE(func_ptr_int)
+
+    # now run the function, calling via ctypes
+    output_value = ct_float(123456.0)
+    errcode = py_mult( 2.0, 3.0, ctypes.byref(output_value) )
+    if errcode != 0:
+        raise RuntimeError('unexpected error')
+    assert output_value.value == 6.0
+
+if __name__=='__main__':
+    test_jit_ctypes()