[BUILD] Allow inject custom pass via phase (#408)

python/tvm/build_module.py

@@ -62,6 +62,7 @@ class BuildConfig(object):
         assert self._old_scope
         BuildConfig.current = self._old_scope
 
+
 BuildConfig.current = BuildConfig()
 
 def build_config(**kwargs):
@@ -102,7 +103,8 @@ def build_config(**kwargs):
         Whether split the loop containing double buffer so
         that the buffer fetching won't contain condition.
 
-    add_lower_pass: list of function(Stmt->Stmt), default=None
+    add_lower_pass: list of tuiple (phase, function(Stmt->Stmt)), default=None
+        phase contains an integer on which optimization pass we apply the pass.
         Additional lowering passes to be applied before make_api.
 
     Returns
@@ -193,11 +195,19 @@ def lower(sch,
     """
     binds, arg_list = get_binds(args, binds)
     cfg = BuildConfig.current
+    add_lower_pass = cfg.add_lower_pass if cfg.add_lower_pass else []
+    lower_phase0 = [x[1] for x in add_lower_pass if x[0] == 0]
+    lower_phase1 = [x[1] for x in add_lower_pass if x[0] == 1]
+    lower_phase2 = [x[1] for x in add_lower_pass if x[0] > 1]
     # normalize schedule first
     sch = sch.normalize()
+    # Phase 0
     bounds = schedule.InferBound(sch)
     stmt = schedule.ScheduleOps(sch, bounds)
     stmt = ir_pass.InjectPrefetch(stmt)
+    for f in lower_phase0:
+        stmt = f(stmt)
+    # Phase 1
     stmt = ir_pass.StorageFlatten(stmt, binds, 64)
     stmt = ir_pass.CanonicalSimplify(stmt)
     if not simple_mode:
@@ -211,13 +221,15 @@ def lower(sch,
         cfg.auto_unroll_max_step,
         cfg.auto_unroll_min_depth,
         cfg.unroll_explicit)
-    if cfg.add_lower_pass:
-        for f in cfg.add_lower_pass:
+    for f in lower_phase1:
         stmt = f(stmt)
+    # Phase 2
     stmt = ir_pass.Simplify(stmt)
     stmt = ir_pass.LowerStorageAccessInfo(stmt)
     stmt = ir_pass.RemoveNoOp(stmt)
     stmt = ir_pass.RewriteUnsafeSelect(stmt)
+    for f in lower_phase2:
+        stmt = f(stmt)
     if simple_mode:
         return stmt
     return ir_pass.MakeAPI(stmt, name, arg_list, 0, cfg.restricted_func)