Re: [Tinycc-devel] manually inlining functions

[Elijah Stone]

On Sat, 1 May 2021, Yakov wrote:

> On this sample using macros speeds the program up 400%

Be that as it may, it's not representative of most application.  For 
instance, cpython's performance increases by only 10-15% with the inliner 
turned on.

(And actually that's misleading, because inlining enables many other 
optimizations.  The impact for tcc if it _only_ added inlining would 
probably be much less.  Unfortunately gcc doesn't seem to be willing to 
inline at -O0.)


> I have recently read a paper about a Linear Scan Register Allocator[1], 
> they claim it gives you 95% performance or Graph Coloring Register 
> Allocator in basically no time, and requires no SSA.

Yes, linear scan is quite nice.  It's not really compatible with tcc's 
compilation model--nor are most other optimizations, including 
inlining--but I mentioned it because it's probably the most worthwhile 
optimization a compiler can perform and it's not too difficult.

In the context of a compiler like gcc or llvm, linear scan takes almost no 
time at all.  However it depends on a certain model of code that tcc does 
not provide currently.  Gcc already produces such a model, even without 
optimizations, and linear scan takes advantage of the information which is 
already there; a big part of the reason why tcc is so fast is that it 
produces no such model.  For gcc this is a sunk cost; for tcc, not.

 -E