[GPU][TOPI] Fix cross thread reduction schedule (#414)

src/pass/lower_thread_allreduce.cc

@@ -261,6 +261,7 @@ class ThreadAllreduceBuilder final : public IRMutator {
     if (in_warp_seq.size() != 0) {
       Stmt warp_body = MergeSeq(in_warp_seq);
       seq.emplace_back(IfThenElse::make(in_warp_cond, warp_body));
+      seq.emplace_back(SyncThread("shared"));
     }
     return MergeSeq(seq);
   }

topi/python/topi/cuda/softmax.py

-# pylint: disable=invalid-name, unused-variable, trailing-whitespace 
+# pylint: disable=invalid-name, unused-variable, trailing-whitespace
 """Schedule for softmax operator"""
 import tvm
 
@@ -34,7 +34,7 @@ def schedule_softmax(outs):
     s[expsum].bind(s[expsum].op.axis[0], block_x)
     s[expsum].bind(s[expsum].op.reduce_axis[0], thread_x)
     s[EF].compute_at(s[expsum], s[expsum].op.reduce_axis[0])
-
+    s[expsum].set_store_predicate(thread_x.var.equal(0))
     tx, xi = s[softmax].split(softmax.op.axis[1], nparts=num_thread)
     s[softmax].bind(softmax.op.axis[0], block_x)
     s[softmax].bind(tx, thread_x)

tutorials/language/reduction.py

@@ -108,8 +108,10 @@ print(s[B].op.body)
 xo, xi = s[B].split(s[B].op.axis[0], factor=32)
 s[B].bind(xo, tvm.thread_axis("blockIdx.x"))
 s[B].bind(xi, tvm.thread_axis("threadIdx.y"))
-s[B].bind(s[B].op.reduce_axis[0], tvm.thread_axis("threadIdx.x"))
+tx = tvm.thread_axis("threadIdx.x")
+s[B].bind(s[B].op.reduce_axis[0], tx)
 s[BF].compute_at(s[B], s[B].op.reduce_axis[0])
+s[B].set_store_predicate(tx.var.equal(0))
 fcuda = tvm.build(s, [A, B], "cuda")
 print(fcuda.imported_modules[0].get_source())