Mullapudi2016-GPU schedule default to false

Add an autoscheduler option `mullapudi2016.experimental_gpu_schedule`
which defaults to `false`, such that the autoscheduler will always
generate CPU schedules by default.

This is to preserve the original behavior of the Mullapudi2016 scheduler,
as well as to pass all CI test-benchmark on Buildbot requiring passing
the tests for "CUDA" or "Metal" targets. Especially, for algorithm
pipelines that poorly fits the assumption of the Mullapudi2016 model
(i.e. the cascaded stentil operations).

src/autoschedulers/mullapudi2016/AutoSchedule.cpp

@@ -23,6 +23,9 @@ using std::vector;
 namespace {
 
 struct ArchParams {
+    /** Enable experimental-GPU schedule feature. */
+    bool experimental_gpu_schedule{false};
+
     /** Maximum level of parallelism avalaible. */
     int parallelism{};
 
@@ -2858,7 +2861,7 @@ std::optional<pair<VarOrRVar, VarOrRVar>> Partitioner::vectorize_stage(const Gro
     // Set the vector length as the maximum of the natural vector size of all
     // values produced by the function.
     const auto vec_len = [&]() -> int {
-        if (t.has_gpu_feature()) {
+        if (t.has_gpu_feature() && arch_params.experimental_gpu_schedule) {
             /** Section 5.4 of the Mullapudi2016 article: We configure the
              * auto-scheduler to target the GPU by set- ting the ...,
              * VECTOR_WIDTH to 32.
@@ -2895,7 +2898,7 @@ std::optional<pair<VarOrRVar, VarOrRVar>> Partitioner::vectorize_stage(const Gro
 
         VarOrRVar vec_var(vec_dim_name, is_rvar);
         auto [inner, outer, accepted] = [&]() -> std::tuple<VarOrRVar, VarOrRVar, bool> {
-            if (t.has_gpu_feature()) {
+            if (t.has_gpu_feature() && arch_params.experimental_gpu_schedule) {
                 VarOrRVar inner{vec_var.name() + "_vi", vec_var.is_rvar}, outer{vec_var.name() + "_vo", vec_var.is_rvar};
                 const bool accepted = gpu_tiling.can_vectorize(vec_var, outer, inner, vec_len);
                 return {inner, outer, accepted};
@@ -3052,7 +3055,7 @@ void Partitioner::reorder_dims(Stage f_handle, int stage_num, Definition def,
     }
 
     if (dims != ordering) {
-        if (t.has_gpu_feature()) {
+        if (t.has_gpu_feature() && arch_params.experimental_gpu_schedule) {
             gpu_tiling.canReorder(ordering);
         } else {
             f_handle.reorder(ordering);
@@ -3205,7 +3208,7 @@ void Partitioner::generate_group_cpu_schedule(
         }
 
         if (dims != ordering) {
-            if (t.has_gpu_feature()) {
+            if (t.has_gpu_feature() && arch_params.experimental_gpu_schedule) {
                 gpu_tiling.canReorder(ordering);
             } else {
                 f_handle.reorder(ordering);
@@ -3219,7 +3222,7 @@ void Partitioner::generate_group_cpu_schedule(
         auto vectorized_split = vectorize_stage(g, f_handle, g.output.stage_num, def, g_out, true, t,
                                                 rvars, stg_estimates, sched, gpu_tiling);
 
-        if (t.has_gpu_feature() && vectorized_split) {
+        if (t.has_gpu_feature() && vectorized_split && arch_params.experimental_gpu_schedule) {
             auto [v_i, v_o] = *vectorized_split;
             inner_dims.emplace_back(v_i);
             outer_dims.emplace_back(v_o);
@@ -3265,7 +3268,7 @@ void Partitioner::generate_group_cpu_schedule(
             if ((iter != stg_estimates.end()) && iter->second.defined()) {
                 if (!seq_var.empty()) {
                     VarOrRVar seq(seq_var, (rvars.find(seq_var) != rvars.end()));
-                    if (t.has_gpu_feature()) {
+                    if (t.has_gpu_feature() && arch_params.experimental_gpu_schedule) {
                         gpu_tiling.canReorder({seq, v});
                     } else {
                         f_handle.reorder(seq, v);
@@ -3274,7 +3277,7 @@ void Partitioner::generate_group_cpu_schedule(
                                             {seq_var, var});
                     }
                 }
-                if (t.has_gpu_feature()) {
+                if (t.has_gpu_feature() && arch_params.experimental_gpu_schedule) {
                     auto parallelized_split = gpu_tiling.can_parallelize(v, iter->second);
                     if (parallelized_split) {
                         auto split_vars = *parallelized_split;
@@ -3297,7 +3300,7 @@ void Partitioner::generate_group_cpu_schedule(
         debug(1) << "Insufficient parallelism for " << f_handle.name() << "\n";
     }
 
-    if (t.has_gpu_feature()) {
+    if (t.has_gpu_feature() && arch_params.experimental_gpu_schedule) {
         gpu_tiling.apply(sched);
     }
 
@@ -3378,7 +3381,7 @@ void Partitioner::generate_group_cpu_schedule(
         vectorize_stage(g, mem_handle, mem.stage_num, mem_def, mem.func, false,
                         t, mem_rvars, mem_estimates, sched, gpu_tiling2);
 
-        if (t.has_gpu_feature()) {
+        if (t.has_gpu_feature() && arch_params.experimental_gpu_schedule) {
             gpu_tiling2.apply(sched);
         }
     }
@@ -3917,6 +3920,7 @@ struct Mullapudi2016 {
         ArchParams arch_params{target.has_gpu_feature()};
         {
             ParamParser parser(params_in.extra);
+            parser.parse("experimental_gpu_schedule", &arch_params.experimental_gpu_schedule);
             parser.parse("parallelism", &arch_params.parallelism);
             parser.parse("last_level_cache_size", &arch_params.last_level_cache_size);
             parser.parse("balance", &arch_params.balance);