The reload_pseudo_compare_func comparator, when used from assign_by_spills, can be non-transitive, indicating A < B < C < A if both A and C satisfy !bitmap_bit_p (&non_reload_pseudos, rAC), but B does not.
This function was originally a proper comparator, and the problematic clause was added to fix PR 57878: https://gcc.gnu.org/ml/gcc-patches/2013-07/msg00732.html That the comparator is invalid implies that that PR, if it still exists, can reappear (but probably under more complicated circumstances). This looks like a sensitive area, so disabling checking is the only obvious approach. * lra-assigns.c (reload_pseudo_compare_func): Add a FIXME. (assign_by_spills): Use non-checking qsort. --- gcc/lra-assigns.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/gcc/lra-assigns.c b/gcc/lra-assigns.c index 2aadeef..a67d1a6 100644 --- a/gcc/lra-assigns.c +++ b/gcc/lra-assigns.c @@ -217,6 +217,7 @@ reload_pseudo_compare_func (const void *v1p, const void *v2p) /* The code below executes rarely as nregs == 1 in most cases. So we should not worry about using faster data structures to check reload pseudos. */ + /* FIXME this makes comparator non-transitive and thus invalid. */ && ! bitmap_bit_p (&non_reload_pseudos, r1) && ! bitmap_bit_p (&non_reload_pseudos, r2)) return diff; @@ -1384,7 +1385,7 @@ assign_by_spills (void) bitmap_ior_into (&non_reload_pseudos, &lra_optional_reload_pseudos); for (iter = 0; iter <= 1; iter++) { - qsort (sorted_pseudos, n, sizeof (int), reload_pseudo_compare_func); + qsort_nochk (sorted_pseudos, n, sizeof (int), reload_pseudo_compare_func); nfails = 0; for (i = 0; i < n; i++) { -- 1.8.3.1
