No optimization works on Alpha?

[Toon Moene]

>  Now I'm beginning to suspect that there are other
>  important non-working optimization features. The following
>  code is painfully slow on my OSF4.0 ev56 Alpha using
>  egcs-980921:

[ Pseudo rank-3 code in C(++) elided ... ]

>  The common integer subexpressions above do not seem to
>  get elimintated, nor are they moved outside the loop as
>  can be seen from the assembler further down. (At least,
>  this is what I think, but I must admit I don't know enough
>  Alpha assembler to actually understand what the compiler
>  is up to)

>  Three things make me think it's a bug in egcs:

Well, let's call it "shortcoming"; the code doesn't generate wrong  
results.

>  * The assembler inner loop is MUCH shorter on my Alpha
>  using OSF4.0 cxx.  * The assembler inner loop is MUCH
>  shorter on my Alpha using egcs g77 and corresponding
>  fortran code.  * The assembler inner loop is MUCH shorter
>  on my pentium with egcs 1.1.

Excellent analysis.  I'll make a prediction (that's my job,  
anyway): changing the line

  int i,j,k;

into

  long i,j,k;

will make this code perform as fast as the Fortran one.  The reason  
is that the Fortran front-end will do this transformation itself  
(courtesy of some hard work by Richard Henderson).  Nobody ever  
bothered to do the same for the C(++) frontend, apparently because  
noone believed that people would try to write Fortran in C ;-)

Rank-1 arrays in C(++) shouldn't exhibit this problem.

For a discussion of Richard's g77 solution (actually in f/com.c),  
see a mail with subject "Re: More than you ever wanted to know about  
Fortran array indexing ;-)" from his hand to the egcs list on the  
5th of October last year in the archives.

Cheers,
Toon.