[PASS] More reliable error message for lower warp (apache#1065)

src/pass/lower_warp_memory.cc

@@ -94,9 +94,13 @@ class WarpStoreCoeffFinder : private IRVisitor {
     CHECK_EQ(m.size(), 2U)
         << "LowerWarpMemory failed due to store index=" << index;
     int coeff;
-    CHECK(arith::GetConstInt(ir::Simplify(m[0]), &coeff) && coeff > 0)
+    Expr mcoeff = ir::Simplify(m[0]);
+
+    CHECK(arith::GetConstInt(mcoeff, &coeff) && coeff > 0)
         << "LowerWarpMemory failed due to store index=" << index
-        << ", require positive constant coefficient on warp index";
+        << ", require positive constant coefficient on warp index " << warp_index_
+        << " but get " << mcoeff;
+
     if (warp_coeff_ != 0) {
       CHECK_EQ(warp_coeff_, coeff)
           << "LowerWarpMemory failed due to two different store coefficient to warp index";
@@ -129,11 +133,6 @@ class WarpIndexFinder : private IRVisitor {
   }
 
  private:
-  void Visit(const NodeRef &node) final {
-    if (warp_index_.defined()) return;
-    IRVisitor::Visit(node);
-  }
-
   /// Visitor implementation
   void Visit_(const AttrStmt *op) final {
     if (op->attr_key == attr::thread_extent) {
@@ -145,7 +144,15 @@ class WarpIndexFinder : private IRVisitor {
             << "Expect threadIdx.x 's size to be equal to warp size("
             << warp_size_ << ")" << " to enable warp memory"
             << " but get " << op->value << " instead";
-        warp_index_ = iv;
+        if (warp_index_.defined()) {
+          CHECK(warp_index_.same_as(iv))
+              << "Find two instance of " << warp_index_->thread_tag
+              << " in the same kernel. "
+              << "Please create it using thread_axis once and reuse the axis "
+              << "across multiple binds in the same kernel";
+        } else {
+          warp_index_ = iv;
+        }
       }
     }
     IRVisitor::Visit_(op);