# Buggy code
def lower_expr(self, expr):
    if expr.op == "binop":
        return self.lower_binop(expr, expr.fn, inplace=False)
    elif expr.op == "inplace_binop":
        return self.lower_binop(expr, expr.fn, inplace=True)
    elif expr.op == "unary":
        value = self.loadvar(expr.value.name)
        if expr.fn == operator.neg:
            res = self.pyapi.number_negative(value)
        elif expr.fn == operator.pos:
            res = self.pyapi.number_positive(value)
        elif expr.fn == operator.not_:
            res = self.pyapi.object_not(value)
            self.check_int_status(res)

            longval = self.builder.zext(res, self.pyapi.long)
            res = self.pyapi.bool_from_long(longval)
        elif expr.fn == operator.invert:
            res = self.pyapi.number_invert(value)
        else:
            raise NotImplementedError(expr)
        self.check_error(res)
        return res
    elif expr.op == "call":
        argvals = [self.loadvar(a.name) for a in expr.args]
        fn = self.loadvar(expr.func.name)
        args = self.pyapi.tuple_pack(argvals)
        if expr.vararg:
            # Expand *args
            new_args = self.pyapi.number_add(args, self.loadvar(expr.vararg.name))
            self.decref(args)
            args = new_args
        if not expr.kws:
            # No named arguments
            ret = self.pyapi.call(fn, args, None)
        else:
            # Named arguments
            keyvalues = [(k, self.loadvar(v.name)) for k, v in expr.kws]
            kws = self.pyapi.dict_pack(keyvalues)
            ret = self.pyapi.call(fn, args, kws)
            self.decref(kws)
        self.decref(args)
        self.check_error(ret)
        return ret
    elif expr.op == "getattr":
        obj = self.loadvar(expr.value.name)
        res = self.pyapi.object_getattr(obj, self._freeze_string(expr.attr))
        self.check_error(res)
        return res
    elif expr.op == "build_tuple":
        items = [self.loadvar(it.name) for it in expr.items]
        res = self.pyapi.tuple_pack(items)
        self.check_error(res)
        return res
    elif expr.op == "build_list":
        items = [self.loadvar(it.name) for it in expr.items]
        res = self.pyapi.list_pack(items)
        self.check_error(res)
        return res
    elif expr.op == "build_map":
        res = self.pyapi.dict_new(expr.size)
        self.check_error(res)
        for k, v in expr.items:
            key = self.loadvar(k.name)
            value = self.loadvar(v.name)
            ok = self.pyapi.dict_setitem(res, key, value)
            self.check_int_status(ok)
        return res
    elif expr.op == "build_set":
        items = [self.loadvar(it.name) for it in expr.items]
        res = self.pyapi.set_new()
        self.check_error(res)
        for it in items:
            ok = self.pyapi.set_add(res, it)
            self.check_int_status(ok)
        return res
    elif expr.op == "getiter":
        obj = self.loadvar(expr.value.name)
        res = self.pyapi.object_getiter(obj)
        self.check_error(res)
        return res
    elif expr.op == "iternext":
        iterobj = self.loadvar(expr.value.name)
        item = self.pyapi.iter_next(iterobj)
        is_valid = cgutils.is_not_null(self.builder, item)
        pair = self.pyapi.tuple_new(2)
        with self.builder.if_else(is_valid) as (then, otherwise):
            with then:
                self.pyapi.tuple_setitem(pair, 0, item)
            with otherwise:
                self.check_occurred()
                # Make the tuple valid by inserting None as dummy
                # iteration "result" (it will be ignored).
                self.pyapi.tuple_setitem(pair, 0, self.pyapi.make_none())
        self.pyapi.tuple_setitem(pair, 1, self.pyapi.bool_from_bool(is_valid))
        return pair
    elif expr.op == "pair_first":
        pair = self.loadvar(expr.value.name)
        first = self.pyapi.tuple_getitem(pair, 0)
        self.incref(first)
        return first
    elif expr.op == "pair_second":
        pair = self.loadvar(expr.value.name)
        second = self.pyapi.tuple_getitem(pair, 1)
        self.incref(second)
        return second
    elif expr.op == "exhaust_iter":
        iterobj = self.loadvar(expr.value.name)
        tup = self.pyapi.sequence_tuple(iterobj)
        self.check_error(tup)
        # Check tuple size is as expected
        tup_size = self.pyapi.tuple_size(tup)
        expected_size = self.context.get_constant(types.intp, expr.count)
        has_wrong_size = self.builder.icmp(lc.ICMP_NE, tup_size, expected_size)
        with cgutils.if_unlikely(self.builder, has_wrong_size):
            self.return_exception(ValueError)
        return tup
    elif expr.op == "getitem":
        value = self.loadvar(expr.value.name)
        index = self.loadvar(expr.index.name)
        res = self.pyapi.object_getitem(value, index)
        self.check_error(res)
        return res
    elif expr.op == "static_getitem":
        value = self.loadvar(expr.value.name)
        index = self.context.get_constant(types.intp, expr.index)
        indexobj = self.pyapi.long_from_ssize_t(index)
        self.check_error(indexobj)
        res = self.pyapi.object_getitem(value, indexobj)
        self.decref(indexobj)
        self.check_error(res)
        return res
    elif expr.op == "getslice":
        target = self.loadvar(expr.target.name)
        start = self.loadvar(expr.start.name)
        stop = self.loadvar(expr.stop.name)

        slicefn = self.get_builtin_obj("slice")
        sliceobj = self.pyapi.call_function_objargs(slicefn, (start, stop))
        self.decref(slicefn)
        self.check_error(sliceobj)

        res = self.pyapi.object_getitem(target, sliceobj)
        self.check_error(res)

        return res

    elif expr.op == "cast":
        val = self.loadvar(expr.value.name)
        self.incref(val)
        return val
    elif expr.op == "phi":
        raise LoweringError("PHI not stripped")

    else:
        raise NotImplementedError(expr)


# Traceback (KeyError)
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/errors.py in new_error_context(fmt_, *args, **kwargs)
768     try:
--> 769         yield
770     except NumbaError as e:

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/lowering.py in lower_block(self, block)
266                                    loc=self.loc, errcls_=defaulterrcls):
--> 267                 self.lower_inst(inst)
268         self.post_block(block)

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/lowering.py in lower_inst(self, inst)
363             ty = self.typeof(inst.target.name)
--> 364             val = self.lower_assign(ty, inst)
365             self.storevar(val, inst.target.name)

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/lowering.py in lower_assign(self, ty, inst)
540         elif isinstance(value, ir.Var):
--> 541             val = self.loadvar(value.name)
542             oty = self.typeof(value.name)

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/lowering.py in loadvar(self, name)
1280         """
-> 1281         ptr = self.getvar(name)
1282         return self.builder.load(ptr)

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/lowering.py in getvar(self, name)
1274         """
-> 1275         return self.varmap[name]
1276

KeyError: 'cum_v.2'

During handling of the above exception, another exception occurred:

LoweringError                             Traceback (most recent call last)
<ipython-input-19-fa852184280b> in <module>
31     return probs
32
---> 33 foo(pol_data, decr_vecs)

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/dispatcher.py in _compile_for_args(self, *args, **kws)
418                     e.patch_message('\n'.join((str(e).rstrip(), help_msg)))
419             # ignore the FULL_TRACEBACKS config, this needs reporting!
--> 420             raise e
421
422     def inspect_llvm(self, signature=None):

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/dispatcher.py in _compile_for_args(self, *args, **kws)
351                 argtypes.append(self.typeof_pyval(a))
352         try:
--> 353             return self.compile(tuple(argtypes))
354         except errors.ForceLiteralArg as e:
355             # Received request for compiler re-entry with the list of arguments

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler_lock.py in _acquire_compile_lock(*args, **kwargs)
30         def _acquire_compile_lock(*args, **kwargs):
31             with self:
---> 32                 return func(*args, **kwargs)
33         return _acquire_compile_lock
34

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/dispatcher.py in compile(self, sig)
792             self._cache_misses[sig] += 1
793             try:
--> 794                 cres = self._compiler.compile(args, return_type)
795             except errors.ForceLiteralArg as e:
796                 def folded(args, kws):

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/dispatcher.py in compile(self, args, return_type)
75
76     def compile(self, args, return_type):
---> 77         status, retval = self._compile_cached(args, return_type)
78         if status:
79             return retval

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/dispatcher.py in _compile_cached(self, args, return_type)
89
90         try:
---> 91             retval = self._compile_core(args, return_type)
92         except errors.TypingError as e:
93             self._failed_cache[key] = e

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/dispatcher.py in _compile_core(self, args, return_type)
102
103         impl = self._get_implementation(args, {})
--> 104         cres = compiler.compile_extra(self.targetdescr.typing_context,
105                                       self.targetdescr.target_context,
106                                       impl,

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler.py in compile_extra(typingctx, targetctx, func, args, return_type, flags, locals, library, pipeline_class)
566     pipeline = pipeline_class(typingctx, targetctx, library,
567                               args, return_type, flags, locals)
--> 568     return pipeline.compile_extra(func)
569
570

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler.py in compile_extra(self, func)
337         self.state.lifted = ()
338         self.state.lifted_from = None
--> 339         return self._compile_bytecode()
340
341     def compile_ir(self, func_ir, lifted=(), lifted_from=None):

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler.py in _compile_bytecode(self)
399         """
400         assert self.state.func_ir is None
--> 401         return self._compile_core()
402
403     def _compile_ir(self):

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler.py in _compile_core(self)
379                 self.state.status.fail_reason = e
380                 if is_final_pipeline:
--> 381                     raise e
382         else:
383             raise CompilerError("All available pipelines exhausted")

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler.py in _compile_core(self)
370             res = None
371             try:
--> 372                 pm.run(self.state)
373                 if self.state.cr is not None:
374                     break

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler_machinery.py in run(self, state)
339                     (self.pipeline_name, pass_desc)
340                 patched_exception = self._patch_error(msg, e)
--> 341                 raise patched_exception
342
343     def dependency_analysis(self):

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler_machinery.py in run(self, state)
330                 pass_inst = _pass_registry.get(pss).pass_inst
331                 if isinstance(pass_inst, CompilerPass):
--> 332                     self._runPass(idx, pass_inst, state)
333                 else:
334                     raise BaseException("Legacy pass in use")

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler_lock.py in _acquire_compile_lock(*args, **kwargs)
30         def _acquire_compile_lock(*args, **kwargs):
31             with self:
---> 32                 return func(*args, **kwargs)
33         return _acquire_compile_lock
34

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler_machinery.py in _runPass(self, index, pss, internal_state)
289             mutated |= check(pss.run_initialization, internal_state)
290         with SimpleTimer() as pass_time:
--> 291             mutated |= check(pss.run_pass, internal_state)
292         with SimpleTimer() as finalize_time:
293             mutated |= check(pss.run_finalizer, internal_state)

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/compiler_machinery.py in check(func, compiler_state)
262
263         def check(func, compiler_state):
--> 264             mangled = func(compiler_state)
265             if mangled not in (True, False):
266                 msg = ("CompilerPass implementations should return True/False. "

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/typed_passes.py in run_pass(self, state)
440
441         # TODO: Pull this out into the pipeline
--> 442         NativeLowering().run_pass(state)
443         lowered = state['cr']
444         signature = typing.signature(state.return_type, *state.args)

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/typed_passes.py in run_pass(self, state)
368                 lower = lowering.Lower(targetctx, library, fndesc, interp,
369                                        metadata=metadata)
--> 370                 lower.lower()
371                 if not flags.no_cpython_wrapper:
372                     lower.create_cpython_wrapper(flags.release_gil)

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/lowering.py in lower(self)
177         if self.generator_info is None:
178             self.genlower = None
--> 179             self.lower_normal_function(self.fndesc)
180         else:
181             self.genlower = self.GeneratorLower(self)

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/lowering.py in lower_normal_function(self, fndesc)
225         # Init argument values
226         self.extract_function_arguments()
--> 227         entry_block_tail = self.lower_function_body()
228
229         # Close tail of entry block

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/lowering.py in lower_function_body(self)
251             bb = self.blkmap[offset]
252             self.builder.position_at_end(bb)
--> 253             self.lower_block(block)
254         self.post_lower()
255         return entry_block_tail

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/lowering.py in lower_block(self, block)
265             with new_error_context('lowering "{inst}" at {loc}', inst=inst,
266                                    loc=self.loc, errcls_=defaulterrcls):
--> 267                 self.lower_inst(inst)
268         self.post_block(block)
269

~/anaconda3/envs/latest_versions38/lib/python3.8/contextlib.py in __exit__(self, type, value, traceback)
129                 value = type()
130             try:
--> 131                 self.gen.throw(type, value, traceback)
132             except StopIteration as exc:
133                 # Suppress StopIteration *unless* it's the same exception that

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/errors.py in new_error_context(fmt_, *args, **kwargs)
774         newerr = errcls(e).add_context(_format_msg(fmt_, args, kwargs))
775         tb = sys.exc_info()[2] if numba.core.config.FULL_TRACEBACKS else None
--> 776         reraise(type(newerr), newerr, tb)
777
778

~/anaconda3/envs/latest_versions38/lib/python3.8/site-packages/numba/core/utils.py in reraise(tp, value, tb)
78     if value.__traceback__ is not tb:
79         raise value.with_traceback(tb)
---> 80     raise value
81
82

LoweringError: Failed in nopython mode pipeline (step: nopython mode backend)
'cum_v.2'

File "<ipython-input-19-fa852184280b>", line 30:
def foo(pol_data, decr_vecs):
<source elided>
else:
cum_v = np.kron(cum_v, v)
^

[1] During: lowering "cum_v.4 = cum_v.2" at <ipython-input-19-fa852184280b> (30)

# Fixed code
def lower_expr(self, expr):
    if expr.op == "binop":
        return self.lower_binop(expr, expr.fn, inplace=False)
    elif expr.op == "inplace_binop":
        return self.lower_binop(expr, expr.fn, inplace=True)
    elif expr.op == "unary":
        value = self.loadvar(expr.value.name)
        if expr.fn == operator.neg:
            res = self.pyapi.number_negative(value)
        elif expr.fn == operator.pos:
            res = self.pyapi.number_positive(value)
        elif expr.fn == operator.not_:
            res = self.pyapi.object_not(value)
            self.check_int_status(res)

            longval = self.builder.zext(res, self.pyapi.long)
            res = self.pyapi.bool_from_long(longval)
        elif expr.fn == operator.invert:
            res = self.pyapi.number_invert(value)
        else:
            raise NotImplementedError(expr)
        self.check_error(res)
        return res
    elif expr.op == "call":
        argvals = [self.loadvar(a.name) for a in expr.args]
        fn = self.loadvar(expr.func.name)
        args = self.pyapi.tuple_pack(argvals)
        if expr.vararg:
            # Expand *args
            new_args = self.pyapi.number_add(args, self.loadvar(expr.vararg.name))
            self.decref(args)
            args = new_args
        if not expr.kws:
            # No named arguments
            ret = self.pyapi.call(fn, args, None)
        else:
            # Named arguments
            keyvalues = [(k, self.loadvar(v.name)) for k, v in expr.kws]
            kws = self.pyapi.dict_pack(keyvalues)
            ret = self.pyapi.call(fn, args, kws)
            self.decref(kws)
        self.decref(args)
        self.check_error(ret)
        return ret
    elif expr.op == "getattr":
        obj = self.loadvar(expr.value.name)
        res = self.pyapi.object_getattr(obj, self._freeze_string(expr.attr))
        self.check_error(res)
        return res
    elif expr.op == "build_tuple":
        items = [self.loadvar(it.name) for it in expr.items]
        res = self.pyapi.tuple_pack(items)
        self.check_error(res)
        return res
    elif expr.op == "build_list":
        items = [self.loadvar(it.name) for it in expr.items]
        res = self.pyapi.list_pack(items)
        self.check_error(res)
        return res
    elif expr.op == "build_map":
        res = self.pyapi.dict_new(expr.size)
        self.check_error(res)
        for k, v in expr.items:
            key = self.loadvar(k.name)
            value = self.loadvar(v.name)
            ok = self.pyapi.dict_setitem(res, key, value)
            self.check_int_status(ok)
        return res
    elif expr.op == "build_set":
        items = [self.loadvar(it.name) for it in expr.items]
        res = self.pyapi.set_new()
        self.check_error(res)
        for it in items:
            ok = self.pyapi.set_add(res, it)
            self.check_int_status(ok)
        return res
    elif expr.op == "getiter":
        obj = self.loadvar(expr.value.name)
        res = self.pyapi.object_getiter(obj)
        self.check_error(res)
        return res
    elif expr.op == "iternext":
        iterobj = self.loadvar(expr.value.name)
        item = self.pyapi.iter_next(iterobj)
        is_valid = cgutils.is_not_null(self.builder, item)
        pair = self.pyapi.tuple_new(2)
        with self.builder.if_else(is_valid) as (then, otherwise):
            with then:
                self.pyapi.tuple_setitem(pair, 0, item)
            with otherwise:
                self.check_occurred()
                # Make the tuple valid by inserting None as dummy
                # iteration "result" (it will be ignored).
                self.pyapi.tuple_setitem(pair, 0, self.pyapi.make_none())
        self.pyapi.tuple_setitem(pair, 1, self.pyapi.bool_from_bool(is_valid))
        return pair
    elif expr.op == "pair_first":
        pair = self.loadvar(expr.value.name)
        first = self.pyapi.tuple_getitem(pair, 0)
        self.incref(first)
        return first
    elif expr.op == "pair_second":
        pair = self.loadvar(expr.value.name)
        second = self.pyapi.tuple_getitem(pair, 1)
        self.incref(second)
        return second
    elif expr.op == "exhaust_iter":
        iterobj = self.loadvar(expr.value.name)
        tup = self.pyapi.sequence_tuple(iterobj)
        self.check_error(tup)
        # Check tuple size is as expected
        tup_size = self.pyapi.tuple_size(tup)
        expected_size = self.context.get_constant(types.intp, expr.count)
        has_wrong_size = self.builder.icmp(lc.ICMP_NE, tup_size, expected_size)
        with cgutils.if_unlikely(self.builder, has_wrong_size):
            self.return_exception(ValueError)
        return tup
    elif expr.op == "getitem":
        value = self.loadvar(expr.value.name)
        index = self.loadvar(expr.index.name)
        res = self.pyapi.object_getitem(value, index)
        self.check_error(res)
        return res
    elif expr.op == "static_getitem":
        value = self.loadvar(expr.value.name)
        index = self.context.get_constant(types.intp, expr.index)
        indexobj = self.pyapi.long_from_ssize_t(index)
        self.check_error(indexobj)
        res = self.pyapi.object_getitem(value, indexobj)
        self.decref(indexobj)
        self.check_error(res)
        return res
    elif expr.op == "getslice":
        target = self.loadvar(expr.target.name)
        start = self.loadvar(expr.start.name)
        stop = self.loadvar(expr.stop.name)

        slicefn = self.get_builtin_obj("slice")
        sliceobj = self.pyapi.call_function_objargs(slicefn, (start, stop))
        self.decref(slicefn)
        self.check_error(sliceobj)

        res = self.pyapi.object_getitem(target, sliceobj)
        self.check_error(res)

        return res

    elif expr.op == "cast":
        val = self.loadvar(expr.value.name)
        self.incref(val)
        return val
    elif expr.op == "phi":
        raise LoweringError("PHI not stripped")

    elif expr.op == "null":
        # Make null value
        return cgutils.get_null_value(self.pyapi.pyobj)

    else:
        raise NotImplementedError(expr)