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Thread-Topic: __builtin_addc support?? 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ZERO COST ABSTRACTIONS lol Sent from Mail for Window= s From: Segher Boessenkool Sent: Wednesday, October 27, 2021 19:17 To: sotrdg sotrdg Cc: gcc@gcc.gnu.org; gcc-request@gcc.gnu.org; gcc-help@gcc.gnu.org Subject: Re: __builtin_addc support?? On Wed, Oct 27, 2021 at 04:12:27PM +0000, sotrdg sotrdg via Gcc-help wrote: > 79173 =96 add-with-carry and subtract-with-borrow support (x86_64 and oth= ers) (gnu.org) > > What I find quite interesting is things like this. > > Since llvm clang provides __builtin_addc __builtin_subc for all targets. = Can we provide something similar? Since currently no solutions we can acces= s carry flag besides x86 Why? We have __builtin_add_overflow, which is a smaller factor, and enough to build up any bigger factors with. You can easily write the same thing in standard C of course, which often is a better plan. If you want exact machine insns as output, write those, i.e., write assembler code, not C. Builtins are not there to please the "C is a portable assembler" crowd: they are there to expose functionality you cannot (conveniently) get using just pure standard C. Segher