[13] RFR(S): 8224658: Unsafe access C2 compile fails with assert(flat != TypePtr::BOTTOM) failed: cannot alias-analyze an untyped ptr: adr_type = NULL

[Vladimir Ivanov]

> http://cr.openjdk.java.net/~thartmann/8224658/webrev.02/

Looks good.

Best regards,
Vladimir Ivanov

> I've also reverted this old fix which is no longer needed because of the _bb_start < _bb_end check:
> http://hg.openjdk.java.net/jdk/jdk/rev/c974c3e10bf7
> 
> On 07.06.19 16:27, Vladimir Ivanov wrote:
>> There are existing usages of Halt for optimizing unsafe accesses (e.g., GraphKit::must_be_not_null),
>> but, as a future enhancement, it would be nice to provide more information about the root cause of
>> the crash. As an example, JDK-8219902 [1] which involved Halt execution manifested as:
>>
>>    # SIGILL (0x4) at pc=0x00007f55b4df37d6, pid=15865, tid=15869
>>    #
>>    # JRE version: OpenJDK Runtime Environment (13.0+9) (build 13-ea+9)
>>    # Java VM: OpenJDK 64-Bit Server VM (13-ea+9, mixed mode, sharing, tiered, compressed oops, g1 gc,
>> linux-amd64)
>>    # Problematic frame:
>>    # J 10152 c2
>> com.sun.tools.javac.tree.Pretty.visitLiteral(Lcom/sun/tools/javac/tree/JCTree$JCLiteral;)V
>> jdk.compiler at 13-ea (282 bytes) @ 0x00007f55b4df37d6 [0x00007f55b4df07a0+0x0000000000003036]
>>
>> Without laborous analysis of generated code, it's impossible to say whether it's a JVM bug or a
>> problem in user code. I believe JVM can do better in such situations and print meaningful error
>> message instead when crashing.
> 
> Yes, I agree that additional output would be very valuable. I'll file a RFE once this is in.
> 
> Thanks,
> Tobias
> 
> [1]
> #  Schedule BB#003 (initial)
>   25	Region	===  25  19  [[ 25  18 ]]  !jvms: Unsafe::putInt @ bci:-1 UnsafeZero::test @ bci:14
>   18	MemBarCPUOrder	===  25  0  10  0  0  [[ 17 ]]  !jvms: Unsafe::putInt @ bci:4 Unsafe::putInt @
> bci:5 UnsafeZero::test @ bci:14
>   17	MachProj	===  18  [[ 16 ]] #0/unmatched !jvms: Unsafe::putInt @ bci:4 Unsafe::putInt @ bci:5
> UnsafeZero::test @ bci:14
>   16	ShouldNotReachHere	===  17  0  0  12  0  [[ 1 ]]  !jvms: Unsafe::putInt @ bci:-1
> UnsafeZero::test @ bci:14
>