[9] RFR(S): 8066763: fatal error "assert(false) failed: unexpected yanked node" in postaloc.cpp:139

[Vladimir Kozlov]

Looks good but rename local from 'req' (required) to 'in' (input) or 'dead'.

Thanks,
Vladimir

On 12/11/14 1:14 AM, Tobias Hartmann wrote:
> Hi,
>
> please review the following patch.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8066763
> Webrev: http://cr.openjdk.java.net/~thartmann/8066763/webrev.00/
>
> Problem:
> A null check for an oop loaded by a LoadNNode (300) consists of a CmpNNode
> (388), a BoolNode (356) and a IfNode (357) [1].
> After matching, the CmpNNode is replaced by a testN_reg node (56) and a jmpCon
> node (55) [2]. With implicit null checks enabled (default), the compiler notices
> that the oop is accessed by a nearby loadINode (131) and optimizes the code by
> using an implicit null check: Instead of checking the oop explicitly, the
> loadINode is moved upwards and executed without a check. Code is added to handle
> the SIGSEGV and throw the corresponding NullPointerException [3].
>
> The problem is that after the optimization the testN_reg node is dead (see [3])
> and triggers the assert in the register allocator. With implicit null checks
> disabled (-XX:-ImplicitNullChecks) the bug does not appear.
>
> Solution:
> The proposed fix checks for dead input nodes after removing the old compare
> node. This removes the dead testN_reg node (see [4]).
>
> Testing:
> - Failing test
> - JPRT
>
> Thanks,
> Tobias
>
> [1] https://bugs.openjdk.java.net/secure/attachment/24158/1_before_matching.png
> [2] https://bugs.openjdk.java.net/secure/attachment/24187/2_global_code_motion.png
> [3] https://bugs.openjdk.java.net/secure/attachment/24159/1_global_code_motion.png
> [4] https://bugs.openjdk.java.net/secure/attachment/24161/3_global_code_motion.png
>