Hi! On Tue, May 24, 2022 at 09:02:00AM +0000, Ian Worthington via Gcc-help wrote: > I'm trying to write some inline assembler but I see that asm() does not support branching to labels, and that asm goto() does not support output (at least prior to gcc 11). > > If I tie them together by declaring an output of the asm() as an input to asm goto() I assume that this will prevent the optimiser from reordering them, but how can I ensure that they are run without any intervening instructions if the goto() has a dependency on the cc generated by the asm(), eg: You cannot. Sorry. > asm ( "algr %[rs],%[rb] \n\t" > : [rs] "+r" (sum) // output > : [rb] "r" (u64b) // input > ); > > asm goto ( "bc 3,%l[done]" // branch if carry bit set (cc 2 or 3) > : // output > : [rs] "r" (sum) // input: ensure this comes after the algr > : // clobbers > : done > ); You have to write to something that is a C variable in that first asm, and read from that in the asm goto. You don't get any advantage over plain C that way, of course, for your example at least. Alternatively you can use a newer compiler. Or you can write the code you want as a real assembler function (in a .s file, not inline asm). gl;hf, Segher
