[16] RFR(S): 8249608: Vector register used by C2 compiled method corrupted at safepoint

[Tobias Hartmann]

Thanks Christian!

Best regards,
Tobias

On 06.08.20 16:28, Christian Hagedorn wrote:
> Hi Tobias
> 
> Looks good to me!
> 
> Best regards,
> Christian
> 
> On 06.08.20 15:53, Tobias Hartmann wrote:
>> Hi,
>>
>> please review the following fix:
>> https://bugs.openjdk.java.net/browse/JDK-8249608
>> http://cr.openjdk.java.net/~thartmann/8249608/webrev.00/
>>
>> The problem is very similar to JDK-8193518 [1], a vector register (ymm0) used for vectorization of a
>> loop in a C2 compiled method is corrupted at a safepoint. Again, the root cause is the superword
>> optimization setting 'max_vector_size' to 16 bytes instead of 32 bytes which leads to the nmethod
>> being marked as !has_wide_vectors and the safepoint handler not saving vector registers [3].
>>
>> This time, the problem is that the superword code only updates 'max_vlen_in_bytes' if 'vlen >
>> max_vlen'. In the failing case, 'vlen' is 4 for all packs (see [4]) but 'vlen_in_bytes' is 16 for
>> the 4 x int StoreVector and 32 for the 4 x long StoreVector. Once we've processed the int
>> StoreVector, we are not updating 'max_vlen_in_bytes' when processing long StoreVector because 'vlen'
>> is equal.
>>
>> The fix is to make sure to always update 'max_vlen_in_bytes'.
>>
>> When looking at JDK-8193518 [1], I've noticed that the corresponding regression test was never
>> pushed. I've added it to this webrev and extended it such that it also covers the new issue.
>>
>> Thanks,
>> Tobias
>>
>> [1] https://bugs.openjdk.java.net/browse/JDK-8193518
>> [2] http://hg.openjdk.java.net/jdk/jdk/file/1f74c0319302/src/hotspot/share/opto/output.cpp#l3313
>> [3]
>> http://hg.openjdk.java.net/jdk/jdk/file/1f74c0319302/src/hotspot/share/runtime/sharedRuntime.cpp#l551
>>
>> [4] -XX:+TraceSuperWord output:
>>
>> After filter_packs
>> packset
>> Pack: 0
>>   align: 0      1101    StoreL    ===  1115  1120  1102  174  [[ 1098 ]]  @long[int:>=0]:exact+any
>> *, idx=6;
>> Memory: @long[int:>=0]:NotNull:exact+any *, idx=6; !orig=993,214,[1012] !jvms: Test::test @ bci:17
>> Test::main @ bci:8
>>   align: 8      1098    StoreL    ===  1115  1101  1099  174  [[ 993 ]]  @long[int:>=0]:exact+any
>> *, idx=6;
>> Memory: @long[int:>=0]:NotNull:exact+any *, idx=6; !orig=214,[1012] !jvms: Test::test @ bci:17
>> Test::main @ bci:8
>>   align: 16      993    StoreL    ===  1115  1098  994  174  [[ 866  214 ]] 
>> @long[int:>=0]:exact+any *,
>> idx=6;  Memory: @long[int:>=0]:NotNull:exact+any *, idx=6; !orig=214,[1012] !jvms: Test::test @
>> bci:17 Test::main @ bci:8
>>   align: 24      214    StoreL    ===  1115  993  212  174  [[ 1120  864  255 ]] 
>> @long[int:>=0]:exact+any *,
>> idx=6;  Memory: @long[int:>=0]:NotNull:exact+any *, idx=6; !orig=[1012] !jvms: Test::test @ bci:17
>> Test::main @ bci:8
>> Pack: 1
>>   align: 0      1097    StoreI    ===  1115  1119  1106  41  [[ 1096 ]]  @int[int:>=0]:exact+any
>> *, idx=8;
>> Memory: @int[int:>=0]:NotNull:exact+any *, idx=8; !orig=989,253,[1009] !jvms: Test::test @ bci:23
>> Test::main @ bci:8
>>   align: 4      1096    StoreI    ===  1115  1097  1104  41  [[ 989 ]]  @int[int:>=0]:exact+any *,
>> idx=8;
>> Memory: @int[int:>=0]:NotNull:exact+any *, idx=8; !orig=253,[1009] !jvms: Test::test @ bci:23
>> Test::main @ bci:8
>>   align: 8      989    StoreI    ===  1115  1096  996  41  [[ 867  253 ]]  @int[int:>=0]:exact+any
>> *, idx=8;
>> Memory: @int[int:>=0]:NotNull:exact+any *, idx=8; !orig=253,[1009] !jvms: Test::test @ bci:23
>> Test::main @ bci:8
>>   align: 12      253    StoreI    ===  1115  989  251  41  [[ 1119  860  255 ]] 
>> @int[int:>=0]:exact+any *,
>> idx=8;  Memory: @int[int:>=0]:NotNull:exact+any *, idx=8; !orig=[1009] !jvms: Test::test @ bci:23
>> Test::main @ bci:8
>>
>> new Vector node:  1491    ReplicateI    === _  41  [[]]  #vectorx[4]:{int}
>> new Vector node:  1492    StoreVector    ===  1115  1119  1106  1491  [[ 1487  1119  255  1486 ]]
>> @int[int:>=0]:NotNull:exact+any *, idx=8; mismatched  Memory: @int[int:>=0]:NotNull:exact+any *,
>> idx=8; !orig=[1097],[989],[253],[1009] !jvms: Test::test @ bci:23 Test::main @ bci:8
>> new Vector node:  1493    ReplicateL    === _  174  [[]]  #vectory[4]:{long}
>> new Vector node:  1494    StoreVector    ===  1115  1120  1102  1493  [[ 1489  1120  255  1488 ]]
>> @long[int:>=0]:NotNull:exact+any *, idx=6; mismatched  Memory: @long[int:>=0]:NotNull:exact+any *,
>> idx=6; !orig=[1101],[993],[214],[1012] !jvms: Test::test @ bci:17 Test::main @ bci:8
>>