https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87655
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2018-10-19
CC| |rguenth at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
It's not so easy (not an easy fit into existing optimization passes). This
is because 'i' is considered a global variable and the optimization is only
valid because we know that 'i' is zero at program start.
Then for optimizing i = i % 10 to if (i == 10) i = 0; we have to know
that i actually reaches 10 (and not 11).
This means we have to compute sth like the scalar evolution of the memory
'i' which only evolves across multiple invocations of next_trivial().
If this happens in SPEC then other compilers probably pattern-match this
kind of thing ...
A "proper" analysis might transform a function body with local statics
into
reg_static_var = static_var;
while (1)
{
... body ...
}
static_var = reg_static_var;
and analyze multiple invocations as if they were directly in a loop. All
other global input would need to be treated volatile.
Eventually the SCEV infrastructure has enough to hack this up and the
prerequesite would be a single load from the static var at function
entry and a single store at function exit.
