[llvm-dev] [RFC] A new intrinsic, `llvm.blackbox`, to explicitly prevent constprop, die, etc optimizations

[Richard Diamond via llvm-dev]

On Fri, Nov 6, 2015 at 10:35 AM, Joerg Sonnenberger via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On Fri, Nov 06, 2015 at 10:31:23AM -0600, Richard Diamond via llvm-dev
> wrote:
> > On Tue, Nov 3, 2015 at 2:50 PM, Diego Novillo <dnovillo at google.com>
> wrote:
> >
> > > I don't see how this is any different from volatile markers on
> > > loads/stores or memory barriers or several other optimizer blocking
> > > devices.  They generally end up crippling the optimizers without much
> added
> > > benefit.
> > >
> >
> > Volatile must touch memory (right?). Memory is slow.
>
> No, it just must not be optimised away. The CPU is still free to cache
> it.
>

Hm, okay. Well, at anyrate it isn't guaranteed; I will do some tests to
check anyway.

Joerg
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