J. Nick Koston c5c9089e9c [api] Keep the decode loop register resident and inline the varint fast path ...

CodSpeed showed the single virtual costing 7 to 18 percent on the
decode benchmarks. The x86-64 disassembly pointed at the call, not the
switch: passing the field number and wire type alongside the tag plus
a 16 byte union payload kept five values live across the call, so the
compiler spilled this, the end pointer and half of the payload to the
stack and reloaded them for every field.

decode_field() now takes only the tag, the payload pointer (already
the loop cursor) and one scalar that holds the varint or fixed32 value
or the payload length. The generated override wraps them in a
ProtoFieldValue that never exists in memory. On the host the switch
key is the field number derived with one shift and the guard compares
the whole tag against the constant the case declares, which is the
same two instructions the old per wire type dispatch cost.

The loop also handles single byte varints inline instead of going
through the parse result struct, which drops the materialized consumed
count and its add on every tag and small value.

2026-09-07 15:24:33 +02:00

..

api_protobuf.py

[api] Keep the decode loop register resident and inline the varint fast path

2026-09-07 15:24:33 +02:00