[15] RFR(S): 8238178: CTW: C1 compilation fails with assert(sux->loop_depth() != block->loop_depth() || sux->loop_index() == block->loop_index() || loop_through_xhandler) failed: Loop index has to be same

[Nils Eliasson]

+1

Best regards,

//Nils

On 2020-02-10 14:48, Tobias Hartmann wrote:
> Hi Christian,
>
> this looks good to me. Nice test cases!
>
> An additional review would be good, I don't think "S" is justified :D
>
> Best regards,
> Tobias
>
> On 07.02.20 11:42, Christian Hagedorn wrote:
>> Hi
>>
>> Please review the following patch:
>> https://bugs.openjdk.java.net/browse/JDK-8238178
>> http://cr.openjdk.java.net/~chagedorn/8238178/webrev.00/
>>
>> The failing assertion is part of the verification of the IR and states that a successor of a block
>> must always have either the same loop index (as part of the same loop) or a different loop depth
>> when exiting the loop. The latter condition is usually true since an edge to an immediately
>> following loop header block is split and a new block inserted (with loop depth 0). However, if there
>> is a loop that is only executed once on the non-exceptional path but multiple times in case of an
>> exception, the edge is not split and another loop header block could immediately follow (as in the
>> test cases). The loop_through_xhandler variable [1] should cover those cases in the assertion: If a
>> successor of a loop head block 'h' is also a loop head block then the backbranch from 'h' must come
>> from one of its exception handlers.
>>
>> The current code assumes that the block from the backbranch is either an exception handler from the
>> loop head block (as in testSimple()) or is dominated by an exception handler of the loop head block
>> (as in testDominatedByXhandler()). However, this does not cover the case with additional try/catch
>> blocks in a catch block such that the backbranch block is not dominated by any exception handler of
>> the loop head block. For example in [2] (testNestedExceptions()), B5 and B17 have different loop
>> indices and the same depth but B16 is neither dominated by xhandler B1 nor xhandler B2, letting the
>> assertion fail.
>>
>> The fix searches through all blocks in the loop to find an exception handler of the loop header block.
>>
>>
>> Thank you!
>>
>> Best regards,
>> Christian
>>
>>
>> [1]
>> http://hg.openjdk.java.net/jdk/jdk/file/5e402c63694f/src/hotspot/share/c1/c1_RangeCheckElimination.cpp#l1109
>>
>> [2] https://bugs.openjdk.java.net/secure/attachment/86667/nested_exceptions.png