The scf-for-loop-range-folding pass transforms loops of the form
for (i = lb; i < ub; i += step) { use(i * c) }
into
for (j = lb*c; j < ub*c; j += step*c) { use(j) }
This transformation is only valid when c is strictly positive, since
scf.for requires a positive step. When c is zero or negative, the new
step becomes zero or effectively negative (wrapping in unsigned
arithmetic for index type), producing an incorrect loop.
Add a guard that restricts the MulIOp folding to cases where the
loop-invariant multiplier is a statically known positive integer
constant. Non-constant loop-invariant multipliers are also excluded
since their sign cannot be determined at compile time.
Fixes#56235Fixes#116664
Assisted-by: Claude Code
79658d7769