Hello,
Hot/cold partitioning is apparently a hot topic all of a sudden, which
is a good thing of course, because it's in need of some TLC.
The attached patch adds another check the RTL cfg checking
(verify_flow_info) for the partitioning: A hot block can never be
dominated by a cold block (because the dominated block must also be
cold). This trips in PR55121.
I haven't tested this with any profiling tests, but it's bound to
break things. From my POV, whatever gets broken by this patch was
already broken to begin with :-) If you're in CC, it's because I
hope you can help test this patch.
Downside of this patch is that I need dominance info. If it's not
available, I compute and free it. I'm not sure if this works if
dominance info status is DOM_NO_FAST_QUERY, and I don't want to
recompute in this case because IMHO a verifier should be a no-op from
the POV of the rest of the compiler, and updating dominators would
make this patch a not-a-no-op :-)
Thoughts/comments?
Ciao!
Steven
* cfgrtl.c (rtl_verify_flow_info_1): Verify that blocks in the
hot partition are not dominated by blocks in the cold partition.
Index: cfgrtl.c
===================================================================
--- cfgrtl.c (revision 191819)
+++ cfgrtl.c (working copy)
@@ -2033,6 +2033,7 @@ rtl_verify_flow_info_1 (void)
rtx x;
int err = 0;
basic_block bb;
+ bool have_partitions = false;
/* Check the general integrity of the basic blocks. */
FOR_EACH_BB_REVERSE (bb)
@@ -2145,6 +2146,8 @@ rtl_verify_flow_info_1 (void)
n_eh++;
else if (e->flags & EDGE_ABNORMAL)
n_abnormal++;
+
+ have_partitions |= is_crossing;
}
if (n_eh && !find_reg_note (BB_END (bb), REG_EH_REGION, NULL_RTX))
@@ -2263,6 +2268,40 @@ rtl_verify_flow_info_1 (void)
}
}
+ /* If there are partitions, do a sanity check on them: A basic block in
+ a cold partition cannot dominate a basic block in a hot partition. */
+ VEC (basic_block, heap) *bbs_in_cold_partition = NULL;
+ if (have_partitions && !err)
+ FOR_EACH_BB (bb)
+ if ((BB_PARTITION (bb) == BB_COLD_PARTITION))
+ VEC_safe_push (basic_block, heap, bbs_in_cold_partition, bb);
+ if (! VEC_empty (basic_block, bbs_in_cold_partition))
+ {
+ bool dom_calculated_here = !dom_info_available_p (CDI_DOMINATORS);
+ basic_block son;
+
+ if (dom_calculated_here)
+ calculate_dominance_info (CDI_DOMINATORS);
+
+ while (! VEC_empty (basic_block, bbs_in_cold_partition))
+ {
+ bb = VEC_pop (basic_block, bbs_in_cold_partition);
+ if ((BB_PARTITION (bb) != BB_COLD_PARTITION))
+ {
+ error ("non-cold basic block %d dominated "
+ "by a block in the cold partition", bb->index);
+ err = 1;
+ }
+ for (son = first_dom_son (CDI_DOMINATORS, bb);
+ son;
+ son = next_dom_son (CDI_DOMINATORS, son))
+ VEC_safe_push (basic_block, heap, bbs_in_cold_partition, son);
+ }
+
+ if (dom_calculated_here)
+ free_dominance_info (CDI_DOMINATORS);
+ }
+
/* Clean up. */
return err;
}
