Add TF_TryEvaluateConstant to the C API and have smart_cond call it.

This effectively plumbs EvaluateConstantTensor to smart_cond. This makes smart_cond even smarter by trying to evaluate the predicate
if it can't statically infer it.

PiperOrigin-RevId: 188073244

1 files changed, 13 insertions, 4 deletions

diff --git a/tensorflow/c/c_api.h b/tensorflow/c/c_api.h
index ad592ef709..b32f574628 100644
--- a/tensorflow/c/c_api.h
+++ b/tensorflow/c/c_api.h
@@ -1275,13 +1275,22 @@ TF_CAPI_EXPORT extern void TF_FunctionGetAttrValueProto(
 // Deleting a function does not remove it from any graphs it was copied to.
 TF_CAPI_EXPORT extern void TF_DeleteFunction(TF_Function* func);
 
+// Attempts to evaluate `output`. This will only be possible if `output` doesn't
+// depend on any graph inputs (this function is safe to call if this isn't the
+// case though).
+//
+// If the evaluation is successful, this function returns true and `output`s
+// value is returned in `result`. Otherwise returns false. An error status is
+// returned if something is wrong with the graph or input. Note that this may
+// return false even if no error status is set.
+TF_CAPI_EXPORT extern unsigned char TF_TryEvaluateConstant(TF_Graph* graph,
+                                                           TF_Output output,
+                                                           TF_Tensor** result,
+                                                           TF_Status* status);
+
 // TODO(josh11b): Register OpDef, available to all operations added
 // to this graph.
 
-// The following two may both benefit from a subgraph-definition API
-// that re-uses most of the graph-definition API.
-// TODO(andydavis): Add functions to a graph.
-
 // --------------------------------------------------------------------------
 // API for driving Graph execution.