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gh-146297: Rewind optimizer when out of space #146298

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gh-146297: Rewind optimizer when out of space #146298

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10 changes: 10 additions & 0 deletions Include/internal/pycore_optimizer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,16 @@ uop_buffer_last(_PyJitUopBuffer *trace)
return trace->next-1;
}

static inline bool
uop_buffer_rewind(_PyJitUopBuffer *trace)
{
if (trace->next <= trace->start) {
return false;
}
trace->next--;
return true;
}

static inline int
uop_buffer_length(_PyJitUopBuffer *trace)
{
Expand Down
45 changes: 31 additions & 14 deletions Python/optimizer_analysis.c
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Original file line number Diff line number Diff line change
Expand Up @@ -488,17 +488,9 @@ optimize_uops(
_PyUOpInstruction *this_instr = NULL;
JitOptRef *stack_pointer = ctx->frame->stack_pointer;

for (int i = 0; i < trace_len; i++) {
int i = 0;
for (; i < trace_len && !ctx->done; i++) {
this_instr = &trace[i];
if (ctx->done) {
// Don't do any more optimization, but
// we still need to reach a terminator for corrctness.
*(ctx->out_buffer.next++) = *this_instr;
if (is_terminator_uop(this_instr)) {
break;
}
continue;
}

int oparg = this_instr->oparg;
opcode = this_instr->opcode;
Expand Down Expand Up @@ -531,10 +523,6 @@ optimize_uops(
assert(STACK_LEVEL() >= 0);
}
}
if (ctx->out_of_space) {
DPRINTF(3, "\n");
DPRINTF(1, "Out of space in abstract interpreter\n");
}
if (ctx->contradiction) {
// Attempted to push a "bottom" (contradiction) symbol onto the stack.
// This means that the abstract interpreter has optimized to trace
Expand All @@ -548,6 +536,35 @@ optimize_uops(
OPT_STAT_INC(optimizer_contradiction);
return 0;
}
if (ctx->out_of_space) {
DPRINTF(3, "\n");
DPRINTF(1, "Out of space in abstract interpreter at length %d\n",
uop_buffer_length(&ctx->out_buffer));
// Rewind to previous instruction and replace with _EXIT_TRACE.
_PyUOpInstruction *curr = uop_buffer_last(&ctx->out_buffer);
while (curr->opcode != _SET_IP) {
if (!uop_buffer_rewind(&ctx->out_buffer)) {
// Reached the start.
return 0;
}
curr = uop_buffer_last(&ctx->out_buffer);
}
Comment on lines +545 to +551
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@cocolato cocolato Mar 23, 2026

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Should we add and set ctx->last_set_ip_offset via _SET_IP instead of the current logic?

assert(curr->opcode == _SET_IP);
int32_t old_target = (int32_t)uop_get_target(curr);
curr->opcode = _EXIT_TRACE;
curr->format = UOP_FORMAT_TARGET;
curr->target = old_target;
DPRINTF(1, "Rewound to length %d\n", uop_buffer_length(&ctx->out_buffer));
}
else {
// Don't do any more optimization, but
// we still need to reach a terminator for correctness.
while (!is_terminator_uop(uop_buffer_last(&ctx->out_buffer))) {
this_instr = &trace[i];
*(ctx->out_buffer.next++) = *this_instr;
i++;
}
}

/* Either reached the end or cannot optimize further, but there
* would be no benefit in retrying later */
Expand Down
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