`main` fails to compile with gcc 15

[richardlau]

Attempting to build the main branch with gcc 15 (tested on Fedora 42 and Ubuntu 25.10 (container)) fails to compile with

cc1plus: error: attribute 'target' argument 'avx10.2-512' is unknown

This appears to have started after the V8 14.2 update -- possibly highway (which is version sniffing the compiler)?

node/deps/v8/third_party/highway/src/hwy/detect_targets.h

Lines 197 to 206 in 72c0fdf

	#ifndef HWY_BROKEN_AVX10_2 // allow override
	// AVX10_2 requires clang >= 20.1 (postpone to 23 due to "avx10.2-512" remnant,
	// only removed in https://github.com/llvm/llvm-project/pull/157034) or
	// gcc >= 15.2 with binutils 2.44.
	#if (HWY_COMPILER_CLANG < 2300) && (HWY_COMPILER_GCC_ACTUAL < 1502)
	#define HWY_BROKEN_AVX10_2 HWY_AVX10_2
	#else
	#define HWY_BROKEN_AVX10_2 0
	#endif
	#endif // HWY_BROKEN_AVX10_2

Switching to clang (on Fedora, clang 20.1.8) or gcc 14 (Ubuntu) succeeds without the error (both of which would cause HWY_BROKEN_AVX10_2 to be defined according to the above snippet).

$ gcc --version
gcc (GCC) 15.2.1 20250808 (Red Hat 15.2.1-1)
Copyright (C) 2025 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$

$ gcc --version
gcc (Ubuntu 15.2.0-4ubuntu4) 15.2.0
Copyright (C) 2025 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$

[richardlau]

I think the error is originating here (specifically the bit that appends avx10.2-512):

node/deps/v8/third_party/highway/src/hwy/ops/set_macros-inl.h

Lines 190 to 198 in f9a83ff

	#if HWY_COMPILER_GCC_ACTUAL >= 1500 || HWY_COMPILER_CLANG >= 2200
	#if HWY_HAVE_EVEX512
	#define HWY_TARGET_STR_AVX10_2 HWY_TARGET_STR_AVX3_SPR ",avx10.2-512"
	#else
	#define HWY_TARGET_STR_AVX10_2 HWY_TARGET_STR_AVX3_SPR ",avx10.2"
	#endif // HWY_HAVE_EVEX512
	#else
	#define HWY_TARGET_STR_AVX10_2 HWY_TARGET_STR_AVX3_SPR
	#endif

It looks like this code was rewritten in google/highway#2563 and now looks like https://github.com/google/highway/blob/b0a4535743aca3e499d8c8d6d4969b94108ea854/hwy/ops/set_macros-inl.h#L196-L205

// Support for avx10.2-512 was removed between clang 22 and 23 without a
// feature test macro.
#if HWY_COMPILER_CLANG >= 2200 && HWY_HAVE_EVEX512
#define HWY_TARGET_STR_AVX10_2 HWY_TARGET_STR_AVX3_SPR ",avx10.2-512"
// Recent compilers drop the -512 suffix because 512 bits are always available.
#elif HWY_COMPILER_GCC_ACTUAL >= 1500 || HWY_COMPILER_CLANG >= 2200
#define HWY_TARGET_STR_AVX10_2 HWY_TARGET_STR_AVX3_SPR ",avx10.2"
#else
#define HWY_TARGET_STR_AVX10_2 HWY_TARGET_STR_AVX3_SPR
#endif

i.e. for gcc 15 it would now use avx10.2 instead of avx10.2-512.

[richardlau]

google/highway@0c160d0#r168636891 and google/highway@989a498

[richardlau]

I can confirm cherry-picking the upstream highway commit fixes the build with gcc 15. It hasn't landed in upstream V8 yet, but I've gone ahead and opened a cherry-pick PR: #60682