Messages in this thread | | | Date | Mon, 7 Jun 2021 09:12:42 -0500 | From | Segher Boessenkool <> | Subject | Re: [RFC] LKMM: Add volatile_if() |
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On Sun, Jun 06, 2021 at 04:37:29PM -0700, Paul E. McKenney wrote: > > > The barrier() thing can work - all we need to do is to simply make it > > > impossible for gcc to validly create anything but a conditional > > > branch. > > > > And the only foolproof way of doing that is by writing a branch.
[ ... ]
> > I am saying that if you depend on that some C code you write will result > > in some particular machine code, without actually *forcing* the compiler > > to output that exact machine code, then you will be disappointed. Maybe > > not today, and maybe it will take years, if you are lucky. > > > > (s/forcing/instructing/ of course, compilers have feelings too!) > > OK, I will bite... > > What would you suggest as a way of instructing the compiler to emit the > conditional branch that we are looking for?
You write it in the assembler code.
Yes, it sucks. But it is the only way to get a branch if you really want one. Now, you do not really need one here anyway, so there may be some other way to satisfy the actual requirements.
Segher
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