# Buggy code
def _strip_phi_nodes(self, func_ir):
    """Strip Phi nodes from ``func_ir``

    For each phi node, put incoming value to their respective incoming
    basic-block at possibly the latest position (i.e. after the latest
    assignment to the corresponding variable).
    """
    exporters = defaultdict(list)
    phis = set()
    # Find all variables that needs to be exported
    for label, block in func_ir.blocks.items():
        for assign in block.find_insts(ir.Assign):
            if isinstance(assign.value, ir.Expr):
                if assign.value.op == "phi":
                    phis.add(assign)
                    phi = assign.value
                    for ib, iv in zip(phi.incoming_blocks, phi.incoming_values):
                        exporters[ib].append((assign.target, iv))

    # Rewrite the blocks with the new exporting assignments
    newblocks = {}
    for label, block in func_ir.blocks.items():
        newblk = copy(block)
        newblocks[label] = newblk

        # strip phis
        newblk.body = [stmt for stmt in block.body if stmt not in phis]

        # insert exporters
        for target, rhs in exporters[label]:
            if rhs is not ir.UNDEFINED:
                assign = ir.Assign(target=target, value=rhs, loc=target.loc)
                # Insert at the earliest possible location; i.e. after the
                # last assignment to rhs
                assignments = [
                    stmt for stmt in newblk.find_insts(ir.Assign) if stmt.target == rhs
                ]
                if assignments:
                    last_assignment = assignments[-1]
                    newblk.insert_after(assign, last_assignment)
                else:
                    newblk.prepend(assign)

    func_ir.blocks = newblocks
    return func_ir


# 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 _strip_phi_nodes(self, func_ir):
    """Strip Phi nodes from ``func_ir``

    For each phi node, put incoming value to their respective incoming
    basic-block at possibly the latest position (i.e. after the latest
    assignment to the corresponding variable).
    """
    exporters = defaultdict(list)
    phis = set()
    # Find all variables that needs to be exported
    for label, block in func_ir.blocks.items():
        for assign in block.find_insts(ir.Assign):
            if isinstance(assign.value, ir.Expr):
                if assign.value.op == "phi":
                    phis.add(assign)
                    phi = assign.value
                    for ib, iv in zip(phi.incoming_blocks, phi.incoming_values):
                        exporters[ib].append((assign.target, iv))

    # Rewrite the blocks with the new exporting assignments
    newblocks = {}
    for label, block in func_ir.blocks.items():
        newblk = copy(block)
        newblocks[label] = newblk

        # strip phis
        newblk.body = [stmt for stmt in block.body if stmt not in phis]

        # insert exporters
        for target, rhs in exporters[label]:
            # If RHS is undefined
            if rhs is ir.UNDEFINED:
                # Put in a NULL initializer
                rhs = ir.Expr.null(loc=target.loc)

            assign = ir.Assign(target=target, value=rhs, loc=target.loc)
            # Insert at the earliest possible location; i.e. after the
            # last assignment to rhs
            assignments = [
                stmt for stmt in newblk.find_insts(ir.Assign) if stmt.target == rhs
            ]
            if assignments:
                last_assignment = assignments[-1]
                newblk.insert_after(assign, last_assignment)
            else:
                newblk.prepend(assign)

    func_ir.blocks = newblocks
    return func_ir