Patch for lowering (#98)

This patch introduces global initialization of lower_extensions
with one functions and replaces with a list of functions.

This change first made in commit 947b407 by @reazulhoque.

Author: PokhodenkoSA

numba/core/lowering.py

@@ -274,6 +274,13 @@ def debug_print(self, msg):
 class Lower(BaseLower):
     GeneratorLower = generators.GeneratorLower
 
+    def __init__(self, context, library, fndesc, func_ir, metadata=None):
+        BaseLower.__init__(self, context, library, fndesc, func_ir, metadata)
+        from numba.parfors.parfor_lowering import _lower_parfor_parallel
+        from numba.parfors import parfor
+        if parfor.Parfor not in lower_extensions:
+            lower_extensions[parfor.Parfor] = [_lower_parfor_parallel]
+
     def pre_block(self, block):
         from numba.core.unsafe import eh
 
@@ -440,7 +447,7 @@ def lower_inst(self, inst):
         else:
             for _class, func in lower_extensions.items():
                 if isinstance(inst, _class):
-                    func(self, inst)
+                    func[-1](self, inst)
                     return
             raise NotImplementedError(type(inst))
 

numba/parfors/parfor_lowering.py

@@ -480,7 +480,7 @@ def _lower_parfor_parallel(lowerer, parfor):
         print("_lower_parfor_parallel done")
 
 # A work-around to prevent circular imports
-lowering.lower_extensions[parfor.Parfor] = _lower_parfor_parallel
+#lowering.lower_extensions[parfor.Parfor] = _lower_parfor_parallel
 
 
 def _create_shape_signature(