Inline threshold relative to frequency

[Christian Thalinger]

On Sun, 2009-11-22 at 00:49 +0100, Ulf Zibis wrote:
> Hi,
> 
> wouldn't it make sense, if the inline threshold for a method would be 
> relative to the frequency of it's usage?
> 
> See the method below. It has 189 bytes of byte code, so it "too big" 
> under default inline threshold.
> As it is called very frequent, performance should increase 
> "dramatically", if it could be inlined, as the pushing of the numerous 
> parameters to stack could be saved.

Well, it "could" be a good idea but it does not necessarily increase
"dramatically" performance.  It's not easy to find good inlining
heuristics that work in all cases.

Inlining a rather big method, like yours, has a number side-effects to
the caller, most importantly:

a) it becomes bigger -> cache effects
b) register pressure might increase -> worse register allocation (but
could be the other way around)

Also note that not all architectures use the stack for passing call
arguments.  Even x86_64 has enough argument registers for this
particular method.

-- Christian