Re: forall and do loop

highegg wrote:
On Jul 27, 2:33 pm, Tobias Burnus <bur...@xxxxxxxx> wrote:
On Jul 27, 11:55 am, highegg <high...@xxxxxxxxx> wrote:

Commercial compilers (Intel, EkoPath) even offer the possibility to
use the profiling information for subsequent optimizations, which is
potentially very powerful approach.
GCC has the same - does this make GCC a commercial compiler? ;-)

GCC has the options: -fprofile-generate and -fprofile-use.

That's cool - I didn't know.
Much of the publicity and development for profiling feedback centers around SPEC2000, as that benchmark considers it a "base" optimization. This position has changed since.
Relating to the original topic: if forall doesn't have any importance in SPEC2000, you could suspect that profiling feedback hasn't been trained to do much for it.
Profile feedback options don't have many convenience features. Commercial compilers may have one advantage over gfortran: profiling data independent of specific compiler flag options makes it unnecessary to re-profile each time a new flag is tried.

Depending on the program, performance might be gained or lost. For the
current gfortran 4.3 and the Polyhedron test suite, seehttp://physik.fu-berlin.de/~tburnus/gcc-trunk/benchmark/#rt

As one test gets 24% slower, the few per cent gains for the other
tests average out (in the geometric mean).
(I filled a bugreport about it, #32913.)
This situation applies to commercial compilers as well.
For real applications, it is necessary to profile across a representative group of data sets, to avoid the common situation of optimizing a single case at the expense of several others.
.

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