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Hi,

For some maybe dumb reasons I try to write a portable version of int128.

What is very valuable for this implementation is access to MUL instruction on x86 which provides full 64 x 64 -> 128 bit multiplication. An equally useful on ARM would be UMULH instruction.

Well, the way you can access this on clang / GCC is to use \_\_int128 type or use inline assembly. MSVC provides an intrinsic for this instruction. This defeats the idea of portable int128 reimplementation and makes constexpr implementation of multiplication at least inconvenient.

Maybe there is a hope for me in LLVM. Is there any pattern matcher that is producing MUL instruction of bigger type?

If not, would it be good idea to teach LLVM about it?

Bests,

Paweł