Hi,
I'm currently testing out a GCC optimisation that allows you to
set call argument flags. The current assumptions being:
in parameters => Assume no escape, no clobber (read-only).
ref parameters, classes and pointers => Assume worst case.
default => Assume no escape.
See here for implementation details:
http://gcc.gnu.org/ml/fortran/2010-05/msg00032.html
The idea for the 'in' parameters being that if we have the
following:
--
bool somefunc (in char[] a);
The compiler can assume that whatever parameters are passed, they
do not changes. So the compiler can more aggressively optimise
the following case, for instance.
eg:
--
char[] foo = "bar";
assert(foo == "bar");
somefunc(foo);
assert(foo == "bar");
One problem I've found with this though, is that the front-end
tends to set all library function parameters as STCin, so the
optimisation is fundamentally broken:
eg:
--
int[3] arr = [2,3,1];
arr.sort; // Defined internally as _adSort(in void[], in
TypeInfo);
assert(arr[0] == 1); // Compiler infers as false, throws assert.
I think it would be more than reasonable to fix the frontend here
so that the internal representation better matches that found in
the internal runtime library. Just wanted to pass this by you
guys first.
Regards
Iain.
