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Fix Strict Aliasing Violation

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Even though this failed with non regression bounds on fishtest, merging
it as is to improve the current situation.

Failed Non Regression:
https://tests.stockfishchess.org/tests/view/6988814db0f3ca5200aafb50
LLR: -2.94 (-2.94,2.94) <-1.75,0.25>
Total: 185792 W: 48109 L: 48565 D: 89118
Ptnml(0-2): 553, 21228, 49811, 20730, 574

Previously we had code similar to this
```
alignas(64) std::uint8_t foo[1024];
const auto* int_ptr = reinterpret_cast<const std::int32_t*>(foo);
```

Which is a strict aliasing violation once we dereference int_ptr, which
invokes UB and causes newer gcc version to emit incorrect code.

fixes https://github.com/official-stockfish/Stockfish/issues/6598
fixes https://github.com/official-stockfish/Stockfish/issues/4932

This violation was introduced in PR #3287 and merged in commit 23c385e.
Due to aggressive compiler optimizations, users may need to include
CXXFLAGS=-fno-strict-aliasing as a build argument to ensure a correctly
functioning binary.

Also thanks to @anematode for writing parts of this and realizing this
strict aliasing violation.

closes https://github.com/official-stockfish/Stockfish/pull/6599

Bench: 2668754

Co-Authored-By: Timothy Herchen <timothy.herchen@gmail.com>
This commit is contained in:
Disservin
2026-02-08 15:20:42 +01:00
co-authored by Timothy Herchen
parent fac506bdf3
commit bfeb36eb3d
5 changed files with 53 additions and 31 deletions
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src/nnue/simd.h
+11 -5
View File
@@ -181,11 +181,17 @@ inline __m128i vec_convert_8_16(uint64_t x) {
#define MaxChunkSize 16
#elif USE_NEON
using vec_t = int16x8_t;
using vec_i8_t = int8x16_t;
using psqt_vec_t = int32x4_t;
using vec128_t = uint16x8_t;
using vec_uint_t = uint32x4_t;
using vec_i8x8_t __attribute__((may_alias)) = int8x8_t;
using vec_i16x8_t __attribute__((may_alias)) = int16x8_t;
using vec_i8x16_t __attribute__((may_alias)) = int8x16_t;
using vec_u16x8_t __attribute__((may_alias)) = uint16x8_t;
using vec_i32x4_t __attribute__((may_alias)) = int32x4_t;
using vec_t __attribute__((may_alias)) = int16x8_t;
using vec_i8_t __attribute__((may_alias)) = int8x16_t;
using psqt_vec_t __attribute__((may_alias)) = int32x4_t;
using vec128_t __attribute__((may_alias)) = uint16x8_t;
using vec_uint_t __attribute__((may_alias)) = uint32x4_t;
#define vec_load(a) (*(a))
#define vec_store(a, b) *(a) = (b)
#define vec_add_16(a, b) vaddq_s16(a, b)