Initial sharding support

-shards [N] -- do a simple sharding based on topological ordering of
DAG.

driver/driver.cc

@@ -147,7 +147,8 @@ static llvm::cl::opt<int> IpuNum(
     "ipu-num",
     llvm::cl::desc("Num of ipus, should consistent with subgraph num"),
     llvm::cl::init(1), llvm::cl::cat(HaloOptCat));
-
+static llvm::cl::opt<int> Shards("shards", llvm::cl::desc("Num of shards"),
+                                 llvm::cl::init(-1), llvm::cl::cat(HaloOptCat));
 static llvm::cl::opt<int> BatchesPerStep(
     "batches-per-step", llvm::cl::desc("Specify batches num for each step"),
     llvm::cl::init(1), llvm::cl::cat(HaloOptCat));
@@ -358,6 +359,7 @@ int main(int argc, char** argv) {
   cg_opts.enable_ipu_device = EnableIpuDevice;
   cg_opts.use_ipu_model = UseIpuModel;
   cg_opts.ipu_num = IpuNum;
+  cg_opts.num_shards = Shards;
   cg_opts.batches_per_step = BatchesPerStep;
   cg_opts.api = Api;
   cg_opts.disable_broadcasting = DisableBroadcasting;

include/halo/halo.h

@@ -91,6 +91,7 @@ struct CXXCodeGenOpts {
   bool emit_shared_lib = false;
   const char* linked_odla_lib = nullptr;
   bool save_temps = false;
+  int num_shards = -1;
 };
 
 #define HALO_MODEL_INFO_MAX_OUTPUT_NR 64

include/halo/lib/pass/pass_manager.h

@@ -110,6 +110,7 @@ class HL_API_EXPORT PassManager final {
 
   Pass* AddRISCVLLVMIRCodeGenPass(ConstantDataStorage constant_data_storage,
                                   const std::string& rt_lib_name);
+  Pass* AddShardingPass(int num_shards);
   Pass* AddSplittingPass();
   Pass* AddTFExtensionLegalizerPass();
   Pass* AddTFLiteExtensionLegalizerPass();

include/halo/lib/transforms/sharding.h

@@ -0,0 +1,38 @@
+//===- sharding.h ---------------------------------------------------------===//
+//
+// Copyright (C) 2019-2020 Alibaba Group Holding Limited.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// =============================================================================
+
+#ifndef HALO_LIB_TRANSFORMS_SHARDING_H_
+#define HALO_LIB_TRANSFORMS_SHARDING_H_
+
+#include "halo/lib/pass/pass.h"
+
+namespace halo {
+
+/// This pass splitting a function into sub functions.
+class Sharding final : public FunctionPass {
+ public:
+  Sharding(int shards) : FunctionPass("Sharding"), shards_(shards) {}
+
+  bool RunOnFunction(Function* func) override;
+
+ private:
+  int shards_;
+};
+
+} // end namespace halo.
+
+#endif // HALO_LIB_TRANSFORMS_SHARDING_H_

include/halo/utils/passes_helper.h

@@ -162,6 +162,7 @@ static void PopulateOptPasses(PassManager* pm, const std::string& target,
   if (opts.enable_type_cast) {
     pm->AddTypeCastPass();
   }
+  pm->AddShardingPass(opts.num_shards);
 }
 } // namespace halo
 

lib/pass/pass_manager.cc

@@ -39,6 +39,7 @@
 #include "halo/lib/transforms/onnxextension_legalizer.h"
 #include "halo/lib/transforms/output_rewriter.h"
 #include "halo/lib/transforms/reorder_channel.h"
+#include "halo/lib/transforms/sharding.h"
 #include "halo/lib/transforms/splitting.h"
 #include "halo/lib/transforms/tfextension_legalizer.h"
 #include "halo/lib/transforms/tfliteextension_legalizer.h"
@@ -382,6 +383,10 @@ Pass* PassManager::AddRISCVLLVMIRCodeGenPass(
   return AddPass<RISCVLLVMIRCodeGen>(constant_data_storage);
 }
 
+Pass* PassManager::AddShardingPass(int num_shards) {
+  return AddPass<Sharding>(num_shards);
+}
+
 Pass* PassManager::AddSplittingPass() { return AddPass<Splitting>(); }
 
 Pass* PassManager::AddTFExtensionLegalizerPass() {

lib/transforms/CMakeLists.txt

@@ -30,6 +30,7 @@ set(SRCS
   onnxextension_legalizer.cc
   output_rewriter.cc
   reorder_channel.cc
+  sharding.cc
   splitting.cc
   tfextension_legalizer.cc
   tfliteextension_legalizer.cc

lib/transforms/sharding.cc

@@ -0,0 +1,133 @@
+//===- sharding.cc --------------------------------------------------------===//
+//
+// Copyright (C) 2019-2021 Alibaba Group Holding Limited.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// =============================================================================
+
+#include "halo/lib/transforms/sharding.h"
+
+#include <unordered_map>
+#include <unordered_set>
+
+#include "halo/lib/ir/ir_builder.h"
+
+namespace halo {
+
+static unsigned CountNonConstOps(const Function& func) {
+  unsigned ret = func.Args().size();
+  for (auto& bb : func) {
+    for (auto& ir : *bb) {
+      ret += IsA<Constant>(*ir) ? 0 : 1;
+    }
+  }
+  return ret;
+}
+
+// Simple sharding scheme: try to get equal shards of op.
+static std::unordered_map<IRObject*, int> GetSimpleSharding(
+    const Function& func, unsigned num_shards) {
+  std::unordered_map<IRObject*, int> shardings;
+  auto num_ops = CountNonConstOps(func);
+  const unsigned threshold = (num_shards == 0)
+                                 ? std::numeric_limits<unsigned>::max()
+                                 : (num_ops + num_shards - 1) / num_shards;
+  unsigned curr_shard = 0;
+  unsigned allocated = 0;
+  auto is_avail = [&shardings](const IRObject* n) {
+    for (auto& op : n->GetOperands()) {
+      if (!IsA<Constant>(op) && shardings.count(op.GetOwner()) == 0) {
+        return false;
+      }
+    }
+    return true;
+  };
+
+  // BFS visit.
+  std::unordered_set<IRObject*> workset;
+  for (auto& arg : func.Args()) {
+    workset.insert(arg.get());
+  }
+  for (auto& bb : func) {
+    for (auto& ir : *bb) {
+      if (!IsA<Constant>(ir.get()) && is_avail(ir.get())) {
+        workset.insert(ir.get());
+      }
+    }
+  }
+
+  while (!workset.empty()) {
+    std::unordered_set<IRObject*> next;
+    HLCHECK(curr_shard < num_shards);
+    for (auto& node : workset) {
+      HLCHECK(shardings.count(node) == 0);
+      shardings[node] = curr_shard;
+      if (!IsA<Constant>(node)) {
+        ++allocated;
+      }
+      for (auto& op : node->GetOperands()) {
+        if (shardings.count(op.GetOwner()) == 0 && IsA<Constant>(op)) {
+          shardings[op.GetOwner()] = curr_shard;
+        }
+      }
+    }
+    // check successors
+    for (auto& node : workset) {
+      for (auto& uses : node->GetResultsUses()) {
+        for (auto& user : uses) {
+          auto n = user.GetUse();
+          if (is_avail(n) && shardings.count(n) == 0) {
+            next.insert(n);
+          }
+        }
+      }
+    }
+    if (allocated >= threshold) {
+      ++curr_shard;
+      allocated = 0;
+      for (auto& n : next) {
+        std::cout << " ---- cut:" << n->GetName() << std::endl;
+      }
+    }
+    workset.swap(next);
+  }
+
+  for (auto& bb : func) {
+    for (auto& ir : *bb) {
+      auto inst = ir.get();
+      HLCHECK(shardings.count(inst) != 0);
+      if (shardings.count(inst) == 0) {
+        std::cerr << "[sharding] unallocated: " << inst->GetName() << "\n";
+        shardings[inst] = num_shards - 1;
+      }
+    }
+  }
+  return shardings;
+}
+
+static void ApplySharding(const std::unordered_map<IRObject*, int>& shardings) {
+  for (const auto& kv : shardings) {
+    std::cout << kv.second << ":" << kv.first->GetName() << ":" << std::endl;
+  }
+}
+
+bool Sharding::RunOnFunction(Function* func) {
+  if (shards_ <= 0) {
+    return false;
+  }
+  auto sharding_scheme = GetSimpleSharding(*func, shards_);
+  ApplySharding(sharding_scheme);
+  return false;
+}
+
+} // end namespace halo