Some optimization thoughts (and thanks!)

[Carlo Wood]

On Tue, May 01, 2001 at 11:08:39AM -0400, At150bogomips@aol.com wrote:
> Here are some optimization suggestions:
> 
> * Inlining of all functions with a single caller: This would presumably
>   be done after short-function inlining (to allow wrapper functions to
>   be inlined into their callers, such wrappers are likely have condition
>   checks and such which can be simplified if inlined into the more basic
>   caller; but if the function that a wrapper calls is inlined first, the
>   resulting function may be too large to inline for multiple basic
>   callers).  This removes the performance penalty of breaking code into
>   graspable portions.  Unlike regular inlining, this reduces code size
>   (by removing call/return overhead).  This should not be that difficult
>   to implement, nor add much to compile time, particularly if the
>   call-tree for a program is retained between compilings and partially
>   updated after source modification.

The compiler can't know how often a function is called, only the linker
can.  This would be possible for static functions, but I'd be highly
surpriced when static functions with one caller aren't already inlined :/

[...]
> (I am disappointed that gcc does not surpass all other compilers in
> optimization--gcc should be the best in everything (portability,
> optimization, compile speed, standards conformance, etc.).  It is
> particularly disappointing that gcc seems to miss some common
> optimizations (e.g., loop arrangement to optimize memory access
> patterns).  I am, of course, very happy that gcc is Free--a compiler is
> a system component even if some vendors do not think so.)

I am not a developer of gcc, just a beta tester (or rather someone who
needs the compiler to work for his own work and therefore reports all
bugs he runs into) - but I understood that the priority of version 3.0
is to make the compiler 100% conforming the new standard; only after
it compiles everything attention will be turned to optimisation issues.
There are still many years to go :)

-- 
Carlo Wood <carlo@alinoe.com>