Propagate semantic constants ahead of static rewrites.

This makes it such that semantic constant propagation happens
before any rewrites for e.g. static getitem are performed to
ensure that there are the most constants possible in the IR and
therefore the maximum opportunities for rewrites to spot them.

Fixes numba#5015

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))