Fix sync map

torch/csrc/jit/codegen/cuda/lower2device.cpp

@@ -303,6 +303,9 @@ void GpuLower::lower(Fusion* fusion, DataType index_type) {
   // Depends on thread_pred_map_, validates parallelization collects which
   // tensor views need WAR or RAW syncs
   sync_map_.build(fusion_);
+  if (isDebugDumpEnabled(DebugDumpOption::SyncMap)) {
+    std::cout << sync_map_.toString() << std::endl;
+  }
 
   partialSplitMap().build(fusion_);
 

torch/csrc/jit/codegen/cuda/lower_sync_information.cpp

@@ -483,7 +483,7 @@ void SyncMap::build(Fusion* fusion) {
       } // end for consumers
 
       if (raw_dims.any()) {
-        needs_raw_sync_[producer] = raw_dims;
+        needs_raw_sync_[producer] |= raw_dims;
       }
 
     } // end producer
@@ -492,10 +492,14 @@ void SyncMap::build(Fusion* fusion) {
 
 std::string SyncMap::toString() const {
   std::stringstream ss;
-  ss << "TVs requiring RAW:" << std::endl;
+  ss << "SyncMap:";
+  bool is_first = true;
   for (auto entry : needs_raw_sync_) {
-    ss << "  " << entry.first->toString() << " :: " << entry.second.toString()
-       << std::endl;
+    if (!is_first) {
+      ss << ",";
+    }
+    ss << " " << entry.first->toString() << " -> " << entry.second.toString();
+    is_first = false;
   }
   return ss.str();
 }

torch/csrc/jit/codegen/cuda/test/test_gpu2.cpp

@@ -5040,6 +5040,40 @@ TEST_F(NVFuserTest, FusionValidateParallelize6_CUDA) {
   ASSERT_ANY_THROW(fusion.printKernel());
 }
 
+// Repro of #2046
+TEST_F(NVFuserTest, FusionValidateParallelize7_CUDA) {
+  Fusion fusion;
+  FusionGuard fg(&fusion);
+
+  auto tv0 = makeSymbolicTensor(2);
+  fusion.addInput(tv0);
+
+  auto tv1 = set(tv0);
+  auto tv2 = set(tv1);
+  auto tv3 = set(tv1);
+  fusion.addOutput(tv2);
+  fusion.addOutput(tv3);
+
+  tv1->setMemoryType(MemoryType::Global);
+
+  tv1->axis(0)->parallelize(ParallelType::BIDx);
+  tv1->axis(1)->parallelize(ParallelType::TIDx);
+
+  tv2->axis(1)->parallelize(ParallelType::TIDy);
+  tv3->axis(0)->parallelize(ParallelType::BIDx);
+
+  // tv2 uses tv1 but is not parallelized with BIDx, so a grid sync is
+  // required. It should be placed as a top-level expression.
+
+  GpuLower gpulw(&fusion);
+  TORCH_CHECK(
+      std::any_of(
+          gpulw.kernel()->topLevelExprs().begin(),
+          gpulw.kernel()->topLevelExprs().end(),
+          [](Expr* expr) { return expr->isA<kir::GridSync>(); }),
+      "Grid sync not found");
+}
+
 TEST_F(NVFuserTest, FusionDAGMerging_CUDA) {
   Fusion fusion;
   FusionGuard fg(&fusion);

torch/csrc/jit/codegen/cuda/utils.cpp

@@ -43,7 +43,8 @@ auto parseDebugDumpOptions() {
       {DebugDumpOption::TransformPropagator, false},
       {DebugDumpOption::Cubin, false},
       {DebugDumpOption::Ptx, false},
-      {DebugDumpOption::BankConflictInfo, false}};
+      {DebugDumpOption::BankConflictInfo, false},
+      {DebugDumpOption::SyncMap, false}};
 
   if (const char* dump_options = std::getenv("PYTORCH_NVFUSER_DUMP")) {
     c10::string_view options_view(dump_options);
@@ -106,6 +107,8 @@ auto parseDebugDumpOptions() {
         options_map[DebugDumpOption::Ptx] = true;
       } else if (token == "bank_conflict") {
         options_map[DebugDumpOption::BankConflictInfo] = true;
+      } else if (token == "sync_map") {
+        options_map[DebugDumpOption::SyncMap] = true;
       } else {
         TORCH_CHECK(
             false,
@@ -118,7 +121,7 @@ auto parseDebugDumpOptions() {
             "\tdraw_segmented_fusion, scheduler_params, parallel_dimensions,\n",
             "\tbuffer_reuse_verbose, ptxas_verbose, halo, segmenter_logging,\n",
             "\tperf_debug_verbose, python_definition, python_frontend_debug,\n",
-            "\ttransform_propagator, cubin, ptx, bank_conflict\n");
+            "\ttransform_propagator, cubin, ptx, bank_conflict, sync_map\n");
       }
       options_view = (end_pos != c10::string_view::npos)
           ? options_view.substr(end_pos + 1)

torch/csrc/jit/codegen/cuda/utils.h

@@ -59,7 +59,8 @@ enum class DebugDumpOption {
                        //! path and replay result
   Cubin, //! Dump compiled CUBIN
   Ptx, //! Dump compiled PTX
-  BankConflictInfo //! Dump bank confliction info
+  BankConflictInfo, //! Dump bank confliction info
+  SyncMap //! RAW dependency info
 };
 
 TORCH_CUDA_CU_API bool isDebugDumpEnabled(DebugDumpOption option);