https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77605

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Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |ASSIGNED CC| |spop at gcc dot gnu.org Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org --- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> --- And the reason is IMHO /* Determines the overlapping elements due to accesses CHREC_A and CHREC_B, that are affine functions. This function cannot handle symbolic evolution functions, ie. when initial conditions are parameters, because it uses lambda matrices of integers. */ static void analyze_subscript_affine_affine (tree chrec_a, tree chrec_b, conflict_function **overlaps_a, conflict_function **overlaps_b, tree *last_conflicts) { ... if (i1 > 0 && j1 > 0) { HOST_WIDE_INT niter_a = max_stmt_executions_int (get_chrec_loop (chrec_a)); HOST_WIDE_INT niter_b = max_stmt_executions_int (get_chrec_loop (chrec_b)); HOST_WIDE_INT niter = MIN (niter_a, niter_b); ^^^ ... /* If the overlap occurs outside of the bounds of the loop, there is no dependence. */ if (x1 >= niter || y1 >= niter) we compute the conflict iteration pair to 0, 6 but niter is two here (minimum of two and eight). Changing the above tests to use niter_a and niter_b fixes the issue but we have other niter uses above that. And the question is of course how to represent "last_conflict" here -- it is supposed to be an iteration number which hopefully is in-range for both loops (fixing the above code to properly use niter_a/b makes it so for _this_ case). "last_conflicts" is not very well documented ("This field stores the information about the iteration domain validity of the dependence relation."). Patch that needs testing (and a 2nd eye): Index: gcc/tree-data-ref.c =================================================================== --- gcc/tree-data-ref.c (revision 240176) +++ gcc/tree-data-ref.c (working copy) @@ -2686,13 +2682,13 @@ analyze_subscript_affine_affine (tree ch if (niter > 0) { - HOST_WIDE_INT tau2 = MIN (FLOOR_DIV (niter - i0, i1), - FLOOR_DIV (niter - j0, j1)); + HOST_WIDE_INT tau2 = MIN (FLOOR_DIV (niter_a - i0, i1), + FLOOR_DIV (niter_b - j0, j1)); HOST_WIDE_INT last_conflict = tau2 - (x1 - i0)/i1; /* If the overlap occurs outside of the bounds of the loop, there is no dependence. */ - if (x1 >= niter || y1 >= niter) + if (x1 >= niter_a || y1 >= niter_b) { *overlaps_a = conflict_fn_no_dependence (); *overlaps_b = conflict_fn_no_dependence (); with this patch we get (compute_affine_dependence stmt_a: _2 = c[b.5_22][_1]; stmt_b: c[b.5_22][a.7_23] = _3; (analyze_overlapping_iterations (chrec_a = {6, +, 1}_2) (chrec_b = {0, +, 1}_1) (analyze_miv_subscript (analyze_subscript_affine_affine (overlaps_a = [0 + 1 * x_1]) (overlaps_b = [6 + 1 * x_1])) ) (overlap_iterations_a = [0 + 1 * x_1]) (overlap_iterations_b = [6 + 1 * x_1])) (analyze_overlapping_iterations (chrec_a = {0, +, 1}_2) (chrec_b = {0, +, 1}_2) (overlap_iterations_a = [0]) (overlap_iterations_b = [0])) (Dependence relation cannot be represented by distance vector.) ) The issue was likely introduced by r129797 (not sure if we vectorized the loop immediately after that change).