add example for using vector instructions

example/vector_instr.py

@@ -0,0 +1,151 @@
+'''
+This example shows:
+1) how to use vector instructions
+2) how to take advantage of LLVM loop vectorization to transform scalar     
+   operations to vector operations
+'''
+
+from __future__ import print_function
+import llvm.core as lc
+import llvm.ee as le
+import llvm.passes as lp
+from ctypes import CFUNCTYPE, POINTER, c_int, c_float
+
+def build_manual_vector():
+    mod = lc.Module.new('manual.vector')
+    intty = lc.Type.int(32)
+    vecty = lc.Type.vector(lc.Type.float(), 4)
+    aryty = lc.Type.pointer(lc.Type.float())
+    fnty = lc.Type.function(lc.Type.void(), [aryty, aryty, aryty, intty])
+    fn = mod.add_function(fnty, name='vector_add')
+    bbentry = fn.append_basic_block('entry')
+    bbloopcond = fn.append_basic_block('loop.cond')
+    bbloopbody = fn.append_basic_block('loop.body')
+    bbexit = fn.append_basic_block('exit')
+    builder = lc.Builder.new(bbentry)
+
+    # populate function body
+    in1, in2, out, size = fn.args
+    ZERO = lc.Constant.null(intty)
+    loopi_ptr = builder.alloca(intty)
+    builder.store(ZERO, loopi_ptr)
+
+    builder.branch(bbloopcond)
+    builder.position_at_end(bbloopcond)
+
+    loopi = builder.load(loopi_ptr)
+    loopcond = builder.icmp(lc.ICMP_ULT, loopi, size)
+
+    builder.cbranch(loopcond, bbloopbody, bbexit)
+    builder.position_at_end(bbloopbody)
+
+    vecaryty = lc.Type.pointer(vecty)
+    in1asvec = builder.bitcast(builder.gep(in1, [loopi]), vecaryty)
+    in2asvec = builder.bitcast(builder.gep(in2, [loopi]), vecaryty)
+    outasvec = builder.bitcast(builder.gep(out, [loopi]), vecaryty)
+
+    vec1 = builder.load(in1asvec)
+    vec2 = builder.load(in2asvec)
+
+    vecout = builder.fadd(vec1, vec2)
+
+    builder.store(vecout, outasvec)
+
+    next = builder.add(loopi, lc.Constant.int(intty, 4))
+    builder.store(next, loopi_ptr)
+
+    builder.branch(bbloopcond)
+    builder.position_at_end(bbexit)
+
+    builder.ret_void()
+
+    return mod, fn
+
+
+def build_auto_vector():
+    mod = lc.Module.new('auto.vector')
+    intty = lc.Type.int(32)
+    aryty = lc.Type.pointer(lc.Type.float())
+    fnty = lc.Type.function(lc.Type.void(), [aryty, aryty, aryty, intty])
+    fn = mod.add_function(fnty, name='vector_add')
+    bbentry = fn.append_basic_block('entry')
+    bbloopcond = fn.append_basic_block('loop.cond')
+    bbloopbody = fn.append_basic_block('loop.body')
+    bbexit = fn.append_basic_block('exit')
+    builder = lc.Builder.new(bbentry)
+
+    # populate function body
+    in1, in2, out, size = fn.args
+    in1.add_attribute(lc.ATTR_NO_ALIAS)
+    in2.add_attribute(lc.ATTR_NO_ALIAS)
+    out.add_attribute(lc.ATTR_NO_ALIAS)
+    ZERO = lc.Constant.null(intty)
+    loopi_ptr = builder.alloca(intty)
+    builder.store(ZERO, loopi_ptr)
+
+    builder.branch(bbloopcond)
+    builder.position_at_end(bbloopcond)
+
+    loopi = builder.load(loopi_ptr)
+    loopcond = builder.icmp(lc.ICMP_ULT, loopi, size)
+
+    builder.cbranch(loopcond, bbloopbody, bbexit)
+    builder.position_at_end(bbloopbody)
+
+    in1elem = builder.load(builder.gep(in1, [loopi]))
+    in2elem = builder.load(builder.gep(in2, [loopi]))
+
+    outelem = builder.fadd(in1elem, in2elem)
+
+    builder.store(outelem, builder.gep(out, [loopi]))
+
+    next = builder.add(loopi, lc.Constant.int(intty, 1))
+    builder.store(next, loopi_ptr)
+
+    builder.branch(bbloopcond)
+    builder.position_at_end(bbexit)
+
+    builder.ret_void()
+
+    return mod, fn
+
+def example(title, module_builder, opt):
+    print(title.center(80, '='))
+    mod, fn = module_builder()
+
+    eb = le.EngineBuilder.new(mod).opt(3)
+    if opt:
+        print('opt')
+        tm = eb.select_target()
+        pms = lp.build_pass_managers(mod=mod, tm=tm, opt=3, loop_vectorize=True,
+                                     fpm=False)
+        pms.pm.run(mod)
+
+    print(mod)
+    print(mod.to_native_assembly())
+
+    engine = eb.create()
+    ptr = engine.get_pointer_to_function(fn)
+
+    callable = CFUNCTYPE(None, POINTER(c_float), POINTER(c_float),
+                         POINTER(c_float), c_int)(ptr)
+
+    N = 20
+    in1 = (c_float * N)(*range(N))
+    in2 = (c_float * N)(*range(N))
+    out = (c_float * N)()
+
+    print('in1: ', list(in1))
+    print('in1: ', list(in2))
+
+    callable(in1, in2, out, N)
+
+    print('out', list(out))
+
+
+def main():
+    example('manual vector function', build_manual_vector, False)
+    example('auto vector function', build_auto_vector, True)
+
+if __name__ == '__main__':
+    main()