Re: [RFC] LKMM: Add volatile_if()

[Paul E. McKenney]

On Sun, Jun 06, 2021 at 08:17:40AM -0500, Segher Boessenkool wrote:
> On Sat, Jun 05, 2021 at 09:43:33PM -0700, Paul E. McKenney wrote:
> > So gcc might some day note a do-nothing asm and duplicate it for
> > the sole purpose of collapsing the "then" and "else" clauses.  I
> > guess I need to keep my paranoia for the time being, then.  :-/
> 
> Or a "do-something" asm, even.  What it does is make sure it is executed
> on the real machine exactly like on the abstract machine.  That is how C
> is defined, what a compiler *does*.
> 
> The programmer does not have any direct control over the generated code.

I am not looking for direct control, simply sufficient influence.  ;-)

> > Of course, there is no guarantee that gcc won't learn about
> > assembler constants.  :-/
> 
> I am not sure what you call an "assembler constant" here.  But you can
> be sure that GCC will not start doing anything here.  GCC does not try
> to understand what you wrote in an inline asm, it just fills in the
> operands and that is all.  It can do all the same things to it that it
> can do to any other code of course: duplicate it, deduplicate it,
> frobnicate it, etc.

Apologies, that "assembler constants" should have been "assembler
comments".

							Thanx, Paul