Merge pull request numba#5024 from stuartarchibald/fix/5015

Propagate semantic constants ahead of static rewrites.

numba/compiler.py

@@ -441,9 +441,9 @@ def define_nopython_pipeline(state, name='nopython'):
 
         # pre typing
         if not state.flags.no_rewrites:
-            pm.add_pass(GenericRewrites, "nopython rewrites")
             pm.add_pass(RewriteSemanticConstants, "rewrite semantic constants")
             pm.add_pass(DeadBranchPrune, "dead branch pruning")
+            pm.add_pass(GenericRewrites, "nopython rewrites")
 
         pm.add_pass(InlineClosureLikes,
                     "inline calls to locally defined closures")

numba/tests/test_analysis.py

@@ -633,3 +633,14 @@ def impl(fa):
         FakeArrayType = types.NamedUniTuple(types.int64, 1, FakeArray)
         self.assert_prune(impl, (FakeArrayType,), [None], fa,
                           flags=enable_pyobj_flags)
+
+    def test_semantic_const_propagates_before_static_rewrites(self):
+        # see issue #5015, the ndim needs writing in as a const before
+        # the rewrite passes run to make e.g. getitems static where possible
+        @njit
+        def impl(a, b):
+            return a.shape[:b.ndim]
+
+        args = (np.zeros((5, 4, 3, 2)), np.zeros((1, 1)))
+
+        self.assertPreciseEqual(impl(*args), impl.py_func(*args))