On Sun, Jun 06, 2021 at 11:48:32AM -0700, Linus Torvalds wrote: > On Sun, Jun 6, 2021 at 11:43 AM Segher Boessenkool > <segher@xxxxxxxxxxxxxxxxxxx> wrote: > > > > You truly should have written a branch in tthe asm if you truly wanted > > a branch instruction. > > That's exactly what I don't want to do, and what the original patch by > PeterZ did. Yes, I know. But it is literally the *only* way to *always* get a conditional branch: by writing one. > And to work well, it needs "asm goto", which is so recent that a lot > of compilers don't support it (thank God for clang dragging gcc > kicking and screaming to implement it at all - I'd asked for it over a > decade ago). GCC has had it since 2009. > So you get bad code generation in a lot of cases, which entirely > obviates the _point_ of this all - which is that we can avoid an > expensive operation (a memory barrier) by just doing clever code > generation. > > So if we can't get the clever code generation, it's all pretty much > moot, imnsho. Yes. Segher
