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disabling loongson LASX runtime dispatching everywhere but GCC15+ (#2626)

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Daniel Lemire
2026-03-12 20:40:43 -04:00
committed by GitHub
parent 019bf1dfe0
commit 6065b3b424
3 changed files with 22 additions and 1 deletions
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doc/implementation-selection.md
+3
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@@ -33,6 +33,9 @@ compiles *all* the implementations into the executable. On Intel, it will includ
(icelake, haswell, westmere and fallback), on 64-bit ARM it will include just one since running dispatching is unnecessary, and on PPC
it will include 2 (ppc64 and fallback).
On Loongson processors, LASX runtime dispatching is only enabled on GCC 15+, not on LLVM or older versions of GCC.
Thus unless you compile specifically for LASX or use GCC 15+, you will not benefit from LASX support.
If you know more about where you're going to run and want to save the space, you can disable any of
these implementations at compile time with `-DSIMDJSON_IMPLEMENTATION_X=0` (where X is ICELAKE, HASWELL,
WESTMERE, ARM64, PPC64, LSX, LASX and FALLBACK).
include/simdjson/compiler_check.h
-1
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@@ -119,5 +119,4 @@
#define SIMDJSON_CONSTEVAL 0
#endif // defined(__cpp_consteval) && __cpp_consteval >= 201811L && defined(__cpp_lib_constexpr_string) && __cpp_lib_constexpr_string >= 201907L
#endif // !defined(SIMDJSON_CONSTEVAL)
#endif // SIMDJSON_COMPILER_CHECK_H
include/simdjson/portability.h
+19
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@@ -66,6 +66,25 @@ using std::size_t;
#define SIMDJSON_IS_LASX 1 // We can always run both
#elif defined(__loongarch_sx)
#define SIMDJSON_IS_LSX 1
// Adjust for runtime dispatching support.
#if defined(__GNUC__) && !defined(__clang__) && !defined(__INTEL_COMPILER) && !defined(__NVCOMPILER)
#if __GNUC__ > 15 || (__GNUC__ == 15 && __GNUC_MINOR__ >= 0)
// We are ok, we will support runtime dispatch for LASX.
#else
// We disable runtime dispatch for LASX, which means that we will not be able to use LASX
// even if it is supported by the hardware.
// Loongson users should update to GCC 15 or better.
#define SIMDJSON_IMPLEMENTATION_LASX 0
#endif
#else
// We are not using GCC, so we assume that we can support runtime dispatch for LASX.
// https://godbolt.org/z/jcMnrjYhs
#define SIMDJSON_IMPLEMENTATION_LASX 0
#endif
#endif
#elif defined(__PPC64__) || defined(_M_PPC64)
#define SIMDJSON_IS_PPC64 1