> While I agree that symbolic ranges are a complication and that most
> cases it currently handles are not "value-range" things I do not agree
> with the idea that we can simply remove handling them and deal
> with the fallout in some later point in the future. Eric may also be
> able to show you "real" symbolic value-range magic.
There are a couple of testcases in the testsuite that, I believe, require a
minimal form of support for symbolic ranges: gcc.dg/tree-ssa/vrp94.c and
gnat.dg/opt40.adb. They deal with the following pattern in C:
if (x >= y)
return 1;
z = y - x;
if (z <= 0)
abort ();
return z;
where we want to eliminate the abort. Of course the C version doesn't really
make sense on its own, but it's the translation of the Ada version where the
if (z <= 0)
abort ();
is generated by the compiler (it's a range check in Ada parlance).
I also agree that symbolic ranges are a complication but I don't understand
why they would conceptually be treated differently from literal ranges. Of
course things may been different practically speaking because I also agree
that they are of lesser importance than literal ranges in most cases.
> Note that symbolic ranges are already restricted to PLUS_EXPR
> and MINUS_EXPR (and NEGATE_EXPR I think). There are
> also "symbolic" (non-integer constant) ranges like [&a, &a].
Yes, the current implementation is restricted to additive operations.
--
Eric Botcazou
