[all-commits] [llvm/llvm-project] c96a17: [tsan] Enable __TSAN_HAS_INT128 on s390x and mips6...

[Mauri de Souza Meneguzzo via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c96a176dd15690ed8181c6764b26d0303008a40f
      https://github.com/llvm/llvm-project/commit/c96a176dd15690ed8181c6764b26d0303008a40f
  Author: Mauri de Souza Meneguzzo <mauri870 at gmail.com>
  Date:   2026-07-16 (Thu, 16 Jul 2026)

  Changed paths:
    M compiler-rt/lib/tsan/rtl/tsan_interface.h

  Log Message:
  -----------
  [tsan] Enable __TSAN_HAS_INT128 on s390x and mips64 (#197319)

The s390x exclusion was added in
https://github.com/llvm/llvm-project/commit/b17673816d7f65e07015489993b22049e36b04db
(https://reviews.llvm.org/D105629)
citing lack of hardware 128-bit atomics. s390x does have the CDSG
instruction,
but `alignof(__int128) == 8` on the s390x psABI while CDSG requires
16-byte
alignment, so Clang does not define
`__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16` for
this target. The mips64 exclusion has been present since
`__TSAN_HAS_INT128` was
introduced in
https://github.com/llvm/llvm-project/commit/06bbca9ec4bbc5a103c94c4973797ea4ddf944b5
(https://reviews.llvm.org/D18543) with no documented
rationale. Clang similarly does not define
`__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16`
for mips64.

Both exclusions are unnecessary. When
`__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16` is
not defined, all a128 operations use the SpinMutex-based emulation path,
which
serializes 128-bit accesses under a global lock without requiring any
hardware
CAS16 support.

Verified with Clang (targets: s390x-linux-gnu, mips64-linux-gnuabi64,
mips64el-linux-gnuabi64): all three produce the full set of 12
`__tsan_atomic128_*` symbols with zero `__sync_*_16 / __atomic_*_16`
libcall references.

Runtime testing has not been performed as I lack access to these
architectures.

Relates https://github.com/llvm/llvm-project/pull/196833
For https://github.com/golang/go/issues/61236



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