github-actions[bot] commented on code in PR #63784:
URL: https://github.com/apache/doris/pull/63784#discussion_r3315370093
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be/src/exprs/function/url/find_symbols.h:
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@@ -330,7 +330,69 @@ inline const char* find_first_symbols_sse42(const char*
const begin, const char*
return return_mode == ReturnMode::End ? end : nullptr;
}
-/// NOTE No SSE 4.2 implementation for find_last_symbols_or_null. Not worth to
do.
+template <bool positive, ReturnMode return_mode>
+inline const char* find_last_symbols_sse2(const char* const begin, const char*
const end,
+ const char* symbols, size_t
num_chars) {
+ if (begin >= end) return return_mode == ReturnMode::End ? end : nullptr;
+
+ const char* pos = end;
+
+#if defined(__SSE2__)
+ const auto needles = mm_is_in_prepare(symbols, num_chars);
+ for (; pos - 16 >= begin; pos -= 16) {
+ __m128i bytes = _mm_loadu_si128(reinterpret_cast<const __m128i*>(pos -
16));
Review Comment:
This loop forms `pos - 16` before proving that there are 16 bytes left in
the range. For any runtime `SearchSymbols` call on a string shorter than 16
bytes (for example `trim_in('abc', ' ')` through the new ASCII rtrim path),
`pos` is `end` and `pos - 16` is outside the array before the comparison is
evaluated, which is undefined behavior even if the loop body is skipped. This
is distinct from the scalar-tail issue already raised: the UB happens in the
SIMD loop condition before reaching the tail. Please use the same safe form as
the SSE4.2 helper, e.g. `static_cast<size_t>(pos - begin) >= 16`, before
computing `pos - 16`.
```suggestion
for (; static_cast<size_t>(pos - begin) >= 16; pos -= 16) {
```
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