Re: GNAT function calling overhead

[dewar@cs.nyu.edu (Robert Dewar)]

Kenneth says:

"
This has little to do with function call overhead per se.  The problem
is that GNAT produces ineffient code for subscripting operations on
Matrix variables when the bounds of the matrix are not known at compile
time.  GNAT does somewhat better when the matrix is not passed as an
argument; hence the performance improvement from inlining."

I don't see this, in the inner loop, with checks turned off, the lower
bound calculation should be moved out of the loop. I can't yet duplicate
the reported results. I asked for the code but did not get it yet. 
Certainly for the straightforward way of computing matrix multiplciation
for example, there is no extra overhead in the inner loop in the GNAT
code, at least on the i386 where I am looking at the assembly code.

In my experience, it is futile to guess what might be behind such
differences without the actual code at hand, there can be MANY variables.
In future, if people want to discuss performance differences between
Ada and C on particular code, it would be useful to post the  alledgedly
comparable source code.