I discovered this problem because adding an algebraic transformation to
convert some uge and ult to ieq or ine caused a couple loops to stop
unrolling. Consider the loop:
uint i = 0;
while (true) {
if (i >= 1)
break;
i++;
}
This loop clearly executes exactly one time. Note that uge(x, 1) is
equivalent to ine(x, 0). Changing the condition to 'if (i != 0)' will
also execute exactly one time.
In the added test cases, uge_once correctly get an exact loop trip count
of 1. Without the changes to nir_loop_analyze.c, the ine_once case
detects a maximum loop trip count of zero and does not get an exact loop
trip count.
No changes in shader-db or fossil-db.
v2: Move nir_op_fneu changes to a separate commit.
v3: Rename test cases.
Fixes: 6772a17acc ("nir: Add a loop analysis pass")
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19732>
This test comes from a comment in the loop analysis code.
The ine_zero test checks that zero iteration loops involving ine are
correctly identified.
v2: Add ine_zero test. Suggested by Tim.
v3: Rename test cases.
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19732>
