Re: Static Chain Register on iOS AArch64

[Richard Henderson <rth at redhat dot com>]

On 06/08/2015 10:00 AM, Richard Earnshaw wrote:
> r12 can *also* be clobbered by interworking calls or calls that span
> more than the branch range of a call instruction.  Rare, but possible.

I can only presume from this that nested functions are not reliable now, for 
very large programs.  Unless you somehow force the nested function to be within 
N bytes of the parent function.  A direct call to a static function, but with a 
static chain to its parent frame.

That said, most go closures are already called indirectly.  It's rare, but 
possible, for optimization to see through the construction of a closure and 
produce a direct call.

It ought to be possible to modify the aarch32 backend to force a call to be 
indirect, and thus not be subject to branch islands, whenever the 
SYMBOL_REF_DECL has DECL_STATIC_CHAIN set?


r~