diff --git a/Include/cpython/pystats.h b/Include/cpython/pystats.h index 1c94603c08b9b6..10ac98f2dfebe6 100644 --- a/Include/cpython/pystats.h +++ b/Include/cpython/pystats.h @@ -142,6 +142,7 @@ typedef struct _optimization_stats { uint64_t recursive_call; uint64_t low_confidence; uint64_t unknown_callee; + uint64_t trace_immediately_deopts; uint64_t executors_invalidated; UOpStats opcode[PYSTATS_MAX_UOP_ID + 1]; uint64_t unsupported_opcode[256]; diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-11-26-20-01-07.gh-issue-141976.K8NDmR.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-11-26-20-01-07.gh-issue-141976.K8NDmR.rst new file mode 100644 index 00000000000000..654681515e43e5 --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-11-26-20-01-07.gh-issue-141976.K8NDmR.rst @@ -0,0 +1 @@ +Protect against specialization failures in the tracing JIT compiler for performance reasons. diff --git a/Python/optimizer.c b/Python/optimizer.c index 9db894f0bf054a..7fe914a7a426b9 100644 --- a/Python/optimizer.c +++ b/Python/optimizer.c @@ -610,6 +610,25 @@ _PyJit_translate_single_bytecode_to_trace( target--; } + if (_PyOpcode_Caches[_PyOpcode_Deopt[opcode]] > 0) { + uint16_t backoff = (this_instr + 1)->counter.value_and_backoff; + // adaptive_counter_cooldown is a fresh specialization. + // trigger_backoff_counter is what we set during tracing. + // All tracing backoffs should be freshly specialized or untouched. + // If not, that indicates a deopt during tracing, and + // thus the "actual" instruction executed is not the one that is + // in the instruction stream, but rather the deopt. + // It's important we check for this, as some specializations might make + // no progress (they can immediately deopt after specializing). + // We do this to improve performance, as otherwise a compiled trace + // will just deopt immediately. + if (backoff != adaptive_counter_cooldown().value_and_backoff && + backoff != trigger_backoff_counter().value_and_backoff) { + OPT_STAT_INC(trace_immediately_deopts); + opcode = _PyOpcode_Deopt[opcode]; + } + } + int old_stack_level = _tstate->jit_tracer_state.prev_state.instr_stacklevel; // Strange control-flow