Agner's CPU blog

__builtin_ctz is not portable to all compilers. I don't think there is any difference in performance. Let's keep this discussion on stackoverflow. Remember to use the tag "vector-class-library" on stackoverflow.

No, there is no performance penalty.

Karalinda wrote:

In many cases, there are no good alternatives to Intel's function libraries

Apparently, it is now possible to use the Intel function libraries without the cripple feature. See my previous post "New Clang-based Intel compiler is better"

Language evolves. I am not sure this is the right forum to discuss this.

An optimizing assembler should code mov rax,123 as mov eax,123 because the result is zero-extended into rax anyway. The two instructions should give identical results. Test results may vary for random reasons. Zero extension cannot be used with negative constants. mov rax,-123 is two bytes longer th...

APX, on the other hand, does add decoder complexity. X86 until AVX512 already has 15 - 18 different prefixes, depending on how you count. APX adds just one more prefix (REX2) and extends the number of uses of an existing one (EVEX). This is just an incremental increase in complexity. It should be p...

We have no promise that in 10 years 1024-bit AVX1024 vector won't crush on 512-FPU. And so we'll have to reinvent the wheel for another time, again. The EVEX prefix used by AVX512 and AVX10 has space for extensions to 1024 bit vectors, but not 2048. SVE/2 might support scaling vector width ARM SVE/...

Thanks for the links. As far as I can see from the manuals, the future AVX10.2 processors will be binary compatible with existing AVX512 code. You only have to recompile the code if you want to use the extra registers and new instructions. The advantages of the new features are limited, so I don't e...

Sorry, you can change the CPU name string, but not the "vendor string" that says AuthenticAMD. It is the vendor string that is checked by Intel software.

It appears that moves are eliminated in 64 bit mode, but not in 32 bit mode. Perhaps this explains your results. Try with some other instructions.