How to express the fact that arguments don't escape?

[Tobias Schlüter]

Thomas Koenig wrote:
> On Sat, 2009-08-15 at 18:27 +0200, Tobias Schlüter wrote:
>> I'm a bit worried that this could pessimize code with very short 
>> functions but lots of arguments, i.e. when the copying time becomes 
>> comparable to the runtime.
> 
> I don't think this will be a problem.  SSA tends to generated quite a
> lot of intermediate variables anyway (just look at a typical dump for
> -fdump-tree-optimized), and all the unnecessary stores will be optimized
> away in the generated assembly.  We shouldn't do this if we aren't
> optimizing, though.
> 
> Richard, do you concur?

Well, the stores and copies are meaningful in this case:
  I_2 = I
  g(I_2)
  I = I_2
The stores can't be optimized away.  This means one additional load (I_2 
= I) in the best case, and one more additional load and store (get I 
from memory, store in I_2; get I_2 from memory, store in I) in the worst 
case.

In other words, I'll have to try with some benchmarks.

Cheers,
- Tobi