[mlir][SCF] Do not peel already peeled loops (#71900)

Loop peeling is not beneficial if the step size already divides "ub -
lb". There are currently some simple checks to prevent peeling in such
cases when lb, ub, step are constants. This commit adds support for IR
that is the result of loop peeling in the general case; i.e., lb, ub,
step do not necessarily have to be constants.

This change adds a new affine_map simplification rule for semi-affine
maps that appear during loop peeling and are guaranteed to evaluate to a
constant zero. Affine maps such as:
```
(1) affine_map<()[ub, step] -> ((ub - ub mod step) mod step)
(2) affine_map<()[ub, lb, step] -> ((ub - (ub - lb) mod step - lb) mod step)
(3)                                         ^ may contain additional summands
```
Other affine maps with modulo expressions are not supported by the new
simplification rule.

This fixes #71469.

0 files changed, 0 insertions, 0 deletions