This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: food for optimizer developers


Hi Tim,

> Do you mean you are adding an additional level of functions and hoping 

> for efficient in-lining?

Note that my questions arise in the context of automatic code generation:
  http://cci.lbl.gov/fable
Please compare e.g. the original LAPACK code with the generated C++ code
to see why the C++ code is done the way it is.

A goal more important than speed is that the auto-generated C++ code
is similar to the original Fortran code and not inflated/obfuscated by
constructs meant to cater to optimizers (which change over time anyway).

My original posting shows that gfortran and g++ don't do as good
a job as ifort in generating efficient machine code. Note that the
loss going from gfortran to g++ isn't as bad as going from ifort to
gfortran. This gives me hope that the gcc developers could work over
time towards bringing the performance of the g++-generated code
closer to the original ifort performance.

I think speed will be the major argument against using the C++ code
generated by the automatic converter. If the generated C++ code could somehow
be made to run nearly as fast as the original Fortran compiled with ifort
there wouldn't be any good reason anymore to still develop in Fortran,
or to bother with the complexities of mixing languages.

Ralf


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]