RFR(XS): 8227384: C2 compilation fails with "graph should be schedulable" when running with -XX:-EliminateLocks
vladimir.kozlov at oracle.com
Tue Aug 6 21:12:40 UTC 2019
> The mark word load for unlocking is created after the release lock
> membar with both control and memory set to projections of the
> membar. Because the allocation is non escaping, when the load is later
> processed, its memory is changed to be above the membar while the
> control is unchanged. A precedence edge is added by anti dependence
> checking to force the load above the membar while its control is
> below. As a result, the graph is not schedulable.
This reminds me bug Tobias is working on 8228772 .
On 7/24/19 4:29 AM, Roland Westrelin wrote:
> Here is a new fix:
Expanding Locks before Allocations is good idea. We do eliminate Locks before eliminating
Allocations. Will a load after IGVN optimization folds with load generated in
I don't see offset check in is_new_object_mark_load(). How it known it is load from *mark word*?
> This time the fix makes sure the load of the mark word that causes the
> graph to be unschedulable is properly eliminated. This is achieved by
> proceeding with macro expansions in 2 steps: first all macro nodes
> except allocations and then only allocations. A pass of igvn is perfomed
> between the 2 steps. That's where the load from a newly allocated object
> is eliminated by a new Ideal or Value transformation.
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