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mruby-compiler: fix JMPNOT+JMP optimization for nested alternatives

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The previous optimization for converting JMPNOT+JMP to JMPIF in
alternative patterns had two bugs:

1. It triggered incorrectly for nested alternatives like `1 | 2 | 3`
   (parsed as `((1|2)|3)`), causing memory corruption.

2. The chain end detection was wrong - it checked `prev_offset == 0`
   but the chain actually ends when `(pos+2) + offset == 0`.

Fix by:
- Only applying optimization when left pattern is not NODE_PAT_ALT
- Correctly detecting chain end by checking if next_addr == 0
- Properly unlinking the last JMPNOT from the fail chain

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2025-12-24 15:42:51 +09:00
parent bbd5dd690b
commit d1aa722a98
1 changed files with 17 additions and 7 deletions
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mrbgems/mruby-compiler/core/codegen.c
+17 -7
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@@ -4447,16 +4447,26 @@ codegen_pattern(codegen_scope *s, node *pattern, int target, uint32_t *fail_pos,
/* Try left pattern */
codegen_pattern(s, pat_alt->left, target, &left_fail, known_array_len);
/* Optimize: if left_fail is single JMPNOT immediately before here,
* convert to JMPIF and skip generating JMP */
if (left_fail != JMPLINK_START &&
(int32_t)(left_fail + 2) + (int16_t)PEEK_S(s->iseq + left_fail) == 0 &&
left_fail + 2 == s->pc) {
/* Optimize JMPNOT+JMP to JMPIF when:
* 1. Left pattern is not another NODE_PAT_ALT (avoid recursion issues)
* 2. Left pattern generated at least one JMPNOT
* 3. The last JMPNOT is immediately before current position
* In this case, convert JMPNOT to JMPIF and skip generating JMP */
if (node_type(pat_alt->left) != NODE_PAT_ALT &&
left_fail != JMPLINK_START && left_fail + 2 == s->pc) {
/* Extract the previous link from the JMPNOT chain.
* The chain uses relative offsets where the end is marked by
* an offset that points to address 0 (i.e., (pos+2)+offset == 0) */
int16_t prev_offset = (int16_t)PEEK_S(s->iseq + left_fail);
int32_t next_addr = (int32_t)(left_fail + 2) + prev_offset;
uint32_t prev_link = (next_addr == 0) ? JMPLINK_START : (uint32_t)next_addr;
/* Convert JMPNOT to JMPIF */
s->iseq[left_fail - 2] = OP_JMPIF;
/* Link into success_pos chain (currently empty, so offset is 0) */
/* Clear offset to mark end of success chain */
emit_S(s, left_fail, 0);
success_pos = left_fail;
left_fail = JMPLINK_START;
/* Continue with remaining fail chain */
left_fail = prev_link;
}
else {
/* Left succeeded - jump to success */