Target Environment - Cross-compilation

[Andrew Haley]

On 19/01/17 23:55, David Clarke wrote:

> So on x86 we want to optimise away a full fence that immediately
> follows a weakCompareAndSet and on ARM, we don’t.  This could be
> delayed until the code generation phase, but I would like to keep
> the optimisations at the IR or LIR level so that we retain the
> greatest generality for as long as possible and avoid repeating
> similar code in several distinct code generation phases.

There's a related problem on ARMv8.  At the present time we emit
fences very early, which means that we don't generate the STLR/LDAR
instructions we really want for Java volailes.  At the very least this
is inefficient.

> So my questions are “How can the code within a Node find out the
> target environment?" and “Can we fiddle this so that the target
> environment is different from the actual host environment?”

I think that the real answer is to handle all of this properly in the
Graal IR by lowering the nodes in a way that is controlled by the back
end.  This will mean that the compiler will have to be taught about
how to handle the nodes appropriately.

Andrew.