[PATCH][RFC] Make parameter aliasing for Fortran more efficient

[Steve Kargl]

On Mon, Aug 04, 2008 at 05:57:17PM +0200, Richard Guenther wrote:
> 
> Currently for parameters to Fortran functions we mark them aliasing only
> theirselves by creating a heap object which they point to
> 
>  PARM_NOALIAS.594 = &ESCAPED
>  PARM_NOALIAS.594.196+196 = &ESCAPED
>  self = &PARM_NOALIAS.594
> 
> as you may notice that dereferencing self will lead to pointers pointing
> to global memory.  This of course makes parameter aliasing quite
> uneffective for array descriptors, as the actual array data is just a
> pointer in the array descriptor data...  which means the actual data
> just is in global memory and will use regular type tags.
> 
> Now, the fix is easy - just pretend Fortran arguments transitively
> point to distinct memory by doing
> 
>  PARM_NOALIAS.594 = &PARM_NOALIAS.594
>  self = &PARM_NOALIAS.594
> 
> instead.  This allows a whole bunch of optimizations in tonto at least.
> 
> Bootstrap / regtest in progress.  I'd appreciate some other Fortran
> benchmarking (and verification).
> 

It doesn't appear to have much impact on the Polyhedron codes.
Each number below is the 'User time' from time(1) and is an
average of five consecutive runs.  The command line options
for each compiler are

-w -O2 -pipe -march=native -funroll-loops -ftree-vectorize -static

The hardware is x86_64-unknown-freebsd8.0

 gfortran      4.2.5   4.3.2   4.4.0     4.4.0
                              Patched  Unpactched
---------------------------------------------
ac.f90        41.396  17.678   18.984   18.992
aermod.f90    44.768  45.634   46.856   46.822
air.f90       18.408  18.184   17.808   17.872
capacita.f90 104.29  101.99   107.094  111.324
channel.f90   13.24   13.266   12.936   13.02
doduc.f90     50.172  50.882   52.66    52.64
fatigue.f90   21.79   18.874   16.634   16.064
gas_dyn.f90   18.806  15.666   15.726   15.784
induct.f90    65.394  62.058   51.372   51.354
linpk.f90     28.952  28.932   29.442   28.996
mdbx.f90      22.208  21.72    21.68    21.73
nf.f90       191.464 190.306  192.356  186.272
protein.f90   61.196  61.584   64.918   64.89
rnflow.f90    52.07   50.532   50.98    50.864
test_fpu.f90  26.47   27.286   27.78    27.302
tfft.f90       9.122   9.024    9.082    9.31

If anything, there appear to be some regressions between
trunk and 4.3.2.

-- 
Steve