Code optimization <LEA Instruction>

[Jeffrey B. Siegal]

owner-linux-kernel-digest en vger.rutgers.edu wrote:
> On Crusoe I guess the cost of redundant instructions is not so
> significant once they've been through a translation pass, but for those
> instruction streams getting interpreted, and for the speed of
> translation itself, it still makes sense to keep the number of
> instructions (and their size) to a minimum.

Which, interestingly, suggests that -Os (or something like it) is what you
want.

> I wouldn't be surprised if inlining is less important.  Crusoe is a sort
> of JIT and would seem well placed to auto-inline things in the
> appropriate, dynamically determined manner.

Inlining can be important to allow cascading optimizations, as in:

int do_it(mode, arg1, arg2, arg3)
{
  switch(mode) {
  case 1:
     ... break;
  case 2:
     ... break;
  ...
  }
}

int 
fun(args)
{
  ...
  a = do_it(1, arg1, arg2, arg3)
  ...
}

On the other hand, inlining, as a tradeoff of size for speed, might actually
be bad (the out-of-line function can get translated once, but inline it needs
to get translated at each call-site).

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