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gh-131798: Small improvements to remove_unneeded_uops #134554

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May 23, 2025
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gh-131798: Small improvements to remove_unneeded_uops #134554

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3 changes: 2 additions & 1 deletion Python/optimizer_analysis.c
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Original file line number Diff line number Diff line change
Expand Up @@ -558,6 +558,7 @@ const uint16_t op_without_push[MAX_UOP_ID + 1] = {
const bool op_skip[MAX_UOP_ID + 1] = {
[_NOP] = true,
[_CHECK_VALIDITY] = true,
[_CHECK_PERIODIC] = true,
[_SET_IP] = true,
};

Expand Down Expand Up @@ -617,7 +618,7 @@ remove_unneeded_uops(_PyUOpInstruction *buffer, int buffer_size)
while (op_skip[last->opcode]) {
last--;
}
if (op_without_push[last->opcode]) {
if (op_without_push[last->opcode] && op_without_pop[opcode]) {
last->opcode = op_without_push[last->opcode];
opcode = buffer[pc].opcode = op_without_pop[opcode];
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When we are here, we know that op_without_pop[opcode] || op_without_pop_null[opcode] is true. But we should also make sure that op_without_pop[opcode] itself is true, otherwise it is possible to accidentally write 0 as the opcode.

if (op_without_pop[last->opcode]) {
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