Restore constant segment (#5141)

Summary:
Pull Request resolved: #5141

Restore constant segment in deserialize_pte_binary.

Note that programs are not identical afterwards, as we do not store the size of the constant buffer. Instead, the restored program will contain tensor+padding in each buffer.

Reviewed By: dbort

Differential Revision: D62278416

Author: lucylq

exir/_serialize/_program.py

@@ -553,6 +553,24 @@ def _restore_segments(program: Program, segment_data: bytes) -> Program:
                 location=DataLocation.INLINE, index=data_index
             )
 
+    # Replace constants from constant_segment into constant_buffer.
+    if program.constant_segment and len(program.constant_segment.offsets) > 0:
+        buffers: List[Buffer] = []
+        constant_segment = segments[program.constant_segment.segment_index]
+        for i in range(len(program.constant_segment.offsets)):
+            start_offset = program.constant_segment.offsets[i]
+            # Note: this is the original end off set plus any padding between
+            # it and the next start offset.
+            end_offset = (
+                program.constant_segment.offsets[i + 1]
+                if i < len(program.constant_segment.offsets) - 1
+                else len(constant_segment)
+            )
+            buffers.append(Buffer(storage=constant_segment[start_offset:end_offset]))
+        program.constant_buffer = buffers
+        program.constant_segment.segment_index = 0
+        program.constant_segment.offsets = []
+
     # Clear out the segments list since the original Program didn't have one.
     program.segments = []
     return program

exir/_serialize/test/test_program.py

@@ -272,6 +272,14 @@ def constant_segment_with_tensor_alignment(
             f"{segment_table}",
         )
 
+        # Convert back.
+        program2 = deserialize_pte_binary(pte_data)
+        # Programs are the same besides constant_buffer, as deserialization
+        # does not preserve constant segment.
+        self.assertEqual(program2.execution_plan, program.execution_plan)
+        # Number of constant tensors should be the same.
+        self.assertEqual(len(program2.constant_buffer), len(program.constant_buffer))
+
     def test_canonicalize_delegate_indices(self) -> None:
         def make_execution_plan(
             name: str, delegates: List[BackendDelegate]
@@ -462,7 +470,6 @@ def gen_blob_data(size: int, pattern: bytes) -> bytes:
         assert len(ret) == size
         return ret
 
-    @unittest.skip("TODO(T181362263): Update restore segments to restore cords")
     def test_round_trip_with_segments(self) -> None:
         # Create a program with some delegate data blobs.
         program = get_test_program()
@@ -803,6 +810,11 @@ def test_constant_segment_and_delegate_segment(self) -> None:
             + b"\x40\x44\x44",
         )
 
+        # Convert back.
+        program2 = deserialize_pte_binary(pte_data)
+        self.assertEqual(program2.execution_plan, program.execution_plan)
+        self.assertEqual(len(program2.constant_buffer), len(program.constant_buffer))
+
 
 # Common data for extended header tests. The two example values should produce
 # the example data.