PR: fallback remove + comments

Signed-off-by: Chizkiyahu Raful <chizkiyahu.raful@arm.com>
Change-Id: If9f6d3ccc3d5d7cebd69306b7894df16bb4a9088

Author: chizkiyahu

exir/_serialize/_flatbuffer_program.py

@@ -128,12 +128,8 @@ def _convert_double(val: Double) -> Any:
     result = _flatbuffer_t_class(Double)()
     double_val = val.double_val
     if isinstance(double_val, str):
-        if double_val == "inf":
-            result.doubleVal = float("inf")
-        elif double_val == "-inf":
-            result.doubleVal = float("-inf")
-        else:
-            result.doubleVal = float(double_val)
+        # the string is read as a Union of float and string (see exir/schema.py).
+        result.doubleVal = float(double_val)
     else:
         result.doubleVal = double_val
     return result

exir/_serialize/_program.py

@@ -9,7 +9,6 @@
 
 import copy
 import json
-import logging
 import math
 import re
 
@@ -21,7 +20,6 @@
 from executorch.exir._serialize._flatbuffer import (
     _FlatbufferResult,
     _program_flatbuffer_to_json,
-    _program_json_to_flatbuffer,
 )
 from executorch.exir._serialize._flatbuffer_program import _program_to_flatbuffer
 from executorch.exir._serialize._named_data_store import (
@@ -51,8 +49,6 @@
 # endian.
 _HEADER_BYTEORDER: Literal["little"] = "little"
 
-logger = logging.getLogger(__name__)
-
 
 @dataclass
 class PTEFile:
@@ -423,35 +419,6 @@ def _extract_named_data(
     program.named_data = named_data
 
 
-def _program_to_flatbuffer_with_fallback(
-    program: Program,
-    *,
-    constant_tensor_alignment: int,
-    delegate_alignment: Optional[int],
-) -> _FlatbufferResult:
-    """
-    Serializes the Program into a FlatBuffer, with a JSON fallback for robustness.
-
-    The FlatBuffer serialization path is the preferred fast path, offering
-    significantly better runtime performance and lower memory usage in benchmarks.
-    The JSON path is retained solely as a fallback to ensure robustness in cases
-    where FlatBuffer serialization fails.
-    """
-    try:
-        return _program_to_flatbuffer(
-            program,
-            constant_tensor_alignment=constant_tensor_alignment,
-            delegate_alignment=delegate_alignment,
-        )
-    except Exception:
-        logger.exception("FlatBuffer serialization failed. Falling back to JSON path.")
-        return _program_json_to_flatbuffer(
-            _program_to_json(program),
-            constant_tensor_alignment=constant_tensor_alignment,
-            delegate_alignment=delegate_alignment,
-        )
-
-
 def serialize_pte_binary(
     pte_file: PTEFile,
     *,
@@ -557,7 +524,9 @@ def serialize_pte_binary(
         segments_data.append(segment.data)
 
     # Convert to a standard flatbuffer binary.
-    result: _FlatbufferResult = _program_to_flatbuffer_with_fallback(
+    # Prefer the direct flatbuffer path to avoid JSON+flatc roundtrip,
+    # which reduces CPU/memory and avoids temp file I/O.
+    result: _FlatbufferResult = _program_to_flatbuffer(
         program,
         constant_tensor_alignment=constant_tensor_alignment,
         delegate_alignment=delegate_alignment,

exir/_serialize/test/test_flatbuffer_program.py

@@ -69,6 +69,9 @@ def _make_program(self) -> Program:
                         EValue(Int(1)),
                         EValue(Bool(True)),
                         EValue(Double(float("inf"))),
+                        EValue(Double(float("-inf"))),
+                        EValue(Double(float("5e-10"))),
+                        EValue(Double(4.5)),
                         EValue(String("hello")),
                         EValue(IntList([1, 2, 3])),
                         EValue(DoubleList([1.5, 2.5])),