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

[Christian Hagedorn]

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
>