RFR: 8290781: Segfault at PhaseIdealLoop::clone_loop_handle_data_uses [v2]

[Roland Westrelin]

> In the test case, both:
> 
>             v1 = array[i];
> (in the first loop), and
> 
>             v += array[i-1];
> 
> (in the second one) access the same element. The bound check for the
> second access is optimized out and the load of that access becomes
> control dependent on the range check of the first one.
> 
> In the context of loop strip mining, data nodes that are in the outer
> loop are expected to be reachable from the safepoint node. There are
> rare case when it's not the case so I added logic to fix those cases
> before loop cloning. That logic covers both nodes that have control in
> the outer loop and control input in the outer loop. That logic is
> incorrect (in the case of a node with a control input in the outer
> loop): when cloning the first loop body, that logic finds the load
> referenced from the range check in the loop body. That load has a
> control input that's in the inner loop. But the logic only check
> whether it's in the outer loop: anything in the inner loop is also in
> the outer loop with that logic. The control of the load is then
> wrongly updated to be outside the outer loop. That then causes a crash
> because the load is recorded as being in the body of the second loop
> but its control is not.
> 
> The fix I propose stengthen the logic that checks for nodes in the
> outer loop: it checks that the control input is in the outer loop but
> not in the inner loop.

Roland Westrelin has updated the pull request incrementally with two additional commits since the last revision:

 - Update src/hotspot/share/opto/loopopts.cpp
   
   Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
 - Update src/hotspot/share/opto/loopopts.cpp
   
   Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/9997/files
  - new: https://git.openjdk.org/jdk/pull/9997/files/43dfe289..90938577

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9997&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9997&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/9997.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9997/head:pull/9997

PR: https://git.openjdk.org/jdk/pull/9997