[Bugfix][ONNX] Skip constant If node generated by PyTorch (#17383)

* [Bugfix][VTA] Fix FSIM compile error on macOS.

VTA FSIM could not be built on macOS, for it leverages malloc.h and
memalign, yet both have been deprecated and are not provided by
macOS. This issue was captured in #13173.

This commit stops including malloc.h in VTA Runtime as stdlib.h has
provided functions we need.

This commit uses posix_memalign instead of memalign. It is a portable standard function.

* Fix format.

* [Bugfix][ONNX] Skip constant If node generated by PyTorch
This commit adds a check for If nodes for ONNX frontend of Relay
to skip the broadcast if the predicate is constant.
Sometimes PyTorch to ONNX inserts silly if nodes that produce dynamic
ranks, and ONNX frontend of TVM would broadcast the lower dimensions
between branches, which is irrational for some cases, e.g. 5×5×3×4 to
5×5×3×4×1. The predicate of silly if might be constant and reasonable
to skip to avoid the broadcast problem.
This issue was captured in #16898.

* Fix format.

Author: xhmelon

python/tvm/relay/frontend/onnx.py

@@ -4565,6 +4565,23 @@ def _impl_v1(cls, inputs, attr, params):
                     "Attempting to unify ranks but this may produce incorrect results."
                 )
                 warnings.warn(warning_msg)
+                # Skip constant If node to avoid irrational broadcast
+                if isinstance(inputs[0], tvm.relay.expr.Constant):
+                    predicate = inputs[0].data.asnumpy()[0]
+                    node_name = attr["tvm_custom"]["name"]
+                    warn_msg_begin = f"Predicate of If node {node_name} is always "
+                    if predicate == np.bool_(True):
+                        warnings.warn(
+                            warn_msg_begin
+                            + "true so only then branch would be executed. Removing else branch. "
+                        )
+                        else_expr = then_expr
+                    elif predicate == np.bool_(False):
+                        warnings.warn(
+                            warn_msg_begin
+                            + "false so only else branch would be executed. Removing then branch. "
+                        )
+                        then_expr = else_expr
                 if len(then_shape) < len(else_shape):
                     then_expr = _op.broadcast_to_like(then_expr, else_expr)
                 else:
@@ -6529,6 +6546,7 @@ def _impl_v11(cls, inputs, attr, params):
 # compatible operators that do NOT require any conversion.
 _identity_list = []
 
+
 # _convert_map defines maps of name to converter functor(callable)
 # for 1 to 1 mapping, use Renamer if nothing but name is different
 # use AttrCvt if attributes need to be converted