On Sun, Jun 06, 2021 at 11:48:32AM -0700, Linus Torvalds wrote:

On Sun, Jun 6, 2021 at 11:43 AM Segher Boessenkool
[off-list ref] wrote:

quoted

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