[9] RFR(S) 8065618: C2 RA incorrectly removes kill projections

[Vladimir Kozlov]

Thank you, Igor

Vladimir

On 11/21/14 4:57 PM, Igor Veresov wrote:
> Looks good.
>
> igor
>
>> On Nov 21, 2014, at 4:32 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>>
>> http://cr.openjdk.java.net/~kvn/8065618/webrev/
>> https://bugs.openjdk.java.net/browse/JDK-8065618
>>
>> Some nodes have SCMemProj projection node to keep them alive even when their result is not used because they have memory side effects.
>> For example, EncodeISOArrayNode and loadstore nodes like CompareAndSwapPNode. Generated code for such nodes may kill some registers and flags during execution. Killed registers are declared in 'effect' list in mach nodes definitions in .ad files. For each killed register MachProj node is created without use:
>>
>> 112    encode_iso_array        ===  103  125  113  114  108  119  120  121  122  [[ 116  117  118  123  124  127  131  134  102  156 ]] !jvms: ISO_8859_1$Encoder::encode @ bci:32 Test6896617::test @ bci:26
>> 116    MachProj        ===  112  [[]] #1
>> 117    MachProj        ===  112  [[]] #2
>> 118    MachProj        ===  112  [[]] #3
>> 127    SCMemProj       ===  112  [[ 126  136  138  139  140  150  160 ]]   Memory: @BotPTR *+bot, idx=Bot; !jvms: ISO_8859_1$Encoder::encode @ bci:32 Test6896617::test @ bci:26
>> 123    MachProj        ===  112  [[]] #4
>> 124    MachProj        ===  112  [[]] #5
>>
>> Register Allocator in PhaseChaitin::build_ifg_physical() removes nodes which are not used (dead). Nodes with
>>
>> To keep such nodes alive when their result is not used there method PhaseChaitin::add_input_to_liveout() puts node's LiveRange on liveout list when the node has SCMemProj projection.
>>
>> Unfortunately SCMemProj node could be placed in a block in such order that kill MachProj nodes are processed first (as in example above). When those MachProj are processed the def node looks like dead and these nodes are removed from graph. As result killed register is not marked as killed anymore and it could be used after code which kills/modifies it.
>>
>> I was not able to write test with existing VM code. encodeISOArray() method can't be called directly - it is part of sun.nio.cs.ISO_8859_1$Encoder::encode() which calls it in a loop. There is enough code after encodeISOArray() call in encode() method which prevents using the same register after encode(). I have experimental project with intrinsics which hits this problem and I verified the fix with it.
>>
>> Thanks,
>> Vladimir
>>
>>
>>
>>
>