improve comments

python/tvm/relay/transform/fake_quantization_to_integer.py

@@ -205,7 +205,11 @@ def pad(expr, type_map):
     arg = expr.args[0]
     t = type_map[arg]
     pad_value = expr.args[1]
+    ## TF2ONNX will sometimes implement the pad_value as a constant without a quantize
+    ## To support that, the pass lets branches that terminate in a constant through
     if pad_value in type_map:
+        ## if the pad value is calcuated from a dequantize op, it should be in the type map
+        ## and we need to make sure it's affine type matches the arg
         pad_t = type_map[pad_value]
         if not tvm.ir.structural_equal(t, pad_t):
             pad_value = relay.qnn.op.requantize(
@@ -217,6 +221,7 @@ def pad(expr, type_map):
                 out_dtype=t.dtype,
             )
     else:
+        ## If the pad-value is a constant, we need to quantize it
         assert isinstance(pad_value, relay.expr.Constant)
         pad_value = relay.qnn.op.quantize(pad_value, t.scale, t.zero_point)
 

src/relay/transforms/fake_quantization_to_integer.cc

@@ -92,9 +92,14 @@ class SubgraphExtractor : public ExprVisitor {
   }
   const AffineTypeMap GetAffineTypes() { return affine_types_; }
   void VisitExpr(const Expr& expr) override {
+    // When looking for fake quantized subgraphs, we only support data-flow regions of the graph,
+    // i.e. call nodes/tuples/constants/etc. If we see anything else (like control flow) we
+    // abort the rewrite.
     if (expr.as<CallNode>() == nullptr && expr.as<OpNode>() == nullptr &&
         expr.as<TupleNode>() == nullptr && expr.as<TupleGetItemNode>() == nullptr &&
         expr.as<ConstantNode>() == nullptr) {
+      LOG(INFO) << "FakeQuantizationToInteger found a non-dataflow op inside"
+                << " a fake quantize region, aborting this rewrite";
       is_fake_quantized_ = false;
     } else {
       ExprVisitor::VisitExpr(expr);
@@ -172,7 +177,7 @@ class SubgraphMutator : public ExprMutator {
       }
       // Call the rewrite
       Array<ObjectRef> vals = fqfq[op](expr, affine_types_);
-      // Save teh outputs of the rewrite
+      // Save the outputs of the rewrite
       ICHECK(vals.size() == 2)
           << "got the wrong number of returned arguments from FTVMFakeQuantizationToInteger for "
           << AsText(op, false);