Bruno Haible wrote:
> Paolo Bonzini wrote:
>>> But the compiler does not know that fstrcmp is called millions of time and
>>> that this piece of code needs to be optimized for speed rather than for
>>> space.
>> If doing profile-directed optimization, it does know.
>
> However, it is impractical: I never used profile-directed optimization with
> GCC so far, because the steps to put it in place are prohibitive. In a
> just-in-time compiler, such as in Java or C# virtual machines, it can be
> implemented transparently. But in a C compiler, it requires the following
> steps (taken from the GCC manual):
>
> * Compile the source files with `-fprofile-arcs' plus
> optimization and code generation options.
> * Link your object files with `-lgcov' or `-fprofile-arcs' (the
> latter implies the former).
> * Run the program on a representative workload to generate the
> arc profile information.
> * Compile the source files again with the same optimization and
> code generation options plus `-fbranch-probabilities'
.PHONY: profile
profile:
make clean
make CFLAGS="$(CFLAGS) -fprofile-generate"
make check
make mostlyclean
make CFLAGS="$(CFLAGS) -fprofile-use"
CLEANFILES = *.gcda *.gcno
Paolo
