2 Jun
2007
2 Jun
'07
4:06 p.m.
From: Fred Cisin <cisin at xenosoft.com
On Sat, 2 Jun 2007, dwight elvey wrote:
Hi Fred
I'd expect the compile to do things in the needed order. Fetch the
value of N to do something with( do the first increment ), calculate
the address ( in doing so apply the second increment) and store the
value into the array.
Hi Dave
I'd expect it to evaluate the left side of the equation first before
determining the address. A[2]=1. Any other order would not make
sense.
It would to some compiler authors. (who sometimes have a different
reality than you and I do) 
2 Jun
2 Jun
5:05 p.m.
On 2 Jun 2007 at 16:06, dwight elvey wrote:
I'd expect the compile to do things in the needed
order. Fetch the
value of N to do something with( do the first increment ), calculate
the address ( in doing so apply the second increment) and store the
value into the array.
Having spent a few years with FORTRAN optimization, I can safely say
that all a compiler has to do is generate code that produces the
right result. Eliminating, variables, loops, expressions, reduction
in strength, moving instructions, inlining functions and a zillion
other tricks is how you win benchmarks and get contracts.
The thing that really plays hob with automatic optimization of C is
the d*mned pointers, which can pretty much refer to anything.
It's not really safe to assume that a compiler will generate what you
expect for anything other than trivial cases--and sometimes not even
then. But this isn't all bad--it frees the programmer to write code
that is easy to read and leaves the bit-twiddling to the compiler.
Or at least that's the theory.
Anyone remember the FORTRAN "ABNORMAL" declaration?
Cheers,
Chuck
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