Fix edge cases in const_int_bound and fold_scale_axis

src/arith/const_int_bound.cc

@@ -519,8 +519,8 @@ class ConstIntBoundAnalyzer::Impl
    */
   static Entry MakeBound(int64_t min_value, int64_t max_value) {
     Entry e;
-    e.min_value = min_value;
-    e.max_value = max_value;
+    e.min_value = (min_value == kPosInf) ? min_value - 1 : min_value;
+    e.max_value = (max_value == kNegInf) ? max_value + 1 : max_value;
     return e;
   }
   /*!

src/relay/transforms/fold_scale_axis.cc

@@ -243,7 +243,18 @@ class ForwardPrep : private ExprVisitor {
     }
   }
   // Visitor pattern override.
-  void VisitExpr_(const LetNode* call) { LOG(FATAL) << "FoldScaleAxis only accept dataflow-form"; }
+  void VisitExpr_(const LetNode* op) {
+    ExprVisitor::VisitExpr_(op);
+    // do pass through condition
+    // by assigning NullValue<Message>
+    // it means fuse signal cannot pass
+    // through into these subexpressions.
+    auto flazy = [this, op]() {
+      this->Update(op->value, NullValue<Message>());
+      this->Update(op->body, NullValue<Message>());
+    };
+    flist_.push_back(flazy);
+  }
 
   void VisitExpr_(const FunctionNode* op) {
     ExprVisitor::VisitExpr_(op);

tests/python/relay/test_pass_fold_scale_axis.py

@@ -311,6 +311,44 @@ def check(shape, channels, blocking, in_scale):
     check((2, 11, 10, 2, 2), 4, (2, 2), in_scale)
 
 
+def test_fold_fwd_let_fail():
+    """testcase where we canont fold"""
+
+    def before(x, conv_weight, in_bias, in_scale, channels):
+        args = [x, conv_weight, in_bias]
+        x = relay.multiply(x, in_scale)
+        x = relay.nn.relu(x)
+        x = relay.add(x, in_bias)
+        x_var = relay.Var("x_var")
+        y1 = relay.nn.conv2d(
+            x_var,
+            conv_weight,
+            channels=channels,
+            kernel_size=(3, 3),
+            data_layout="NHWC",
+            kernel_layout="HWIO",
+            padding=(1, 1),
+        )
+        z = relay.add(y1, x)
+        let = relay.Let(x_var, x, z)
+        return relay.Function(args, let)
+
+    def check(shape, channels):
+        x = relay.var("x", shape=shape)
+        in_channels = shape[-1]
+        in_bias = relay.var("in_bias", shape=(in_channels,))
+        in_scale = relay.const(_get_positive_scale(size=(in_channels,)))
+        # test depthwise
+        assert in_channels == channels
+        weight = relay.var("weight")
+        y1 = before(x, weight, in_bias, in_scale, channels)
+        y1 = run_opt_pass(y1, transform.InferType())
+        y1_folded = run_opt_pass(y1, transform.ForwardFoldScaleAxis())
+        assert tvm.ir.structural_equal(y1, y1_folded)
+
+    check((2, 11, 10, 4), 4)
+
+
 def test_fold_fwd_negative_scale():
     """Testcase of folding negative scale"""
 

tests/python/unittest/test_arith_const_int_bound.py

@@ -76,6 +76,20 @@ def test_add_sub_bound():
     assert bd.min_value == bd.NEG_INF
     assert bd.max_value == 1
 
+    ## constants with negative or positive max(int64) occassionally show up
+    ## in models, this is to ensure we can handle those cases
+    analyzer.update(x, tvm.arith.ConstIntBound(bd.NEG_INF, bd.NEG_INF), override=True)
+    analyzer.update(y, tvm.arith.ConstIntBound(bd.NEG_INF, bd.POS_INF), override=True)
+    bd = analyzer.const_int_bound(x + y)
+    assert bd.min_value == bd.NEG_INF
+    assert bd.max_value == bd.POS_INF
+
+    analyzer.update(x, tvm.arith.ConstIntBound(bd.POS_INF, bd.POS_INF), override=True)
+    analyzer.update(y, tvm.arith.ConstIntBound(bd.NEG_INF, bd.POS_INF), override=True)
+    bd = analyzer.const_int_bound(x + y)
+    assert bd.min_value == bd.NEG_INF
+    assert bd.max_value == bd.POS_INF
+
 
 def test_mul_bound():
     analyzer = tvm.arith.Analyzer()