[14] RFR(S): 8234617: C1: Incorrect result of field load due to missing narrowing conversion

[Tobias Hartmann]

Thanks Martin!

Best regards,
Tobias

On 02.12.19 11:14, Doerr, Martin wrote:
> +1
> 
> Best regards,
> Martin
> 
>> -----Original Message-----
>> From: hotspot-compiler-dev <hotspot-compiler-dev-
>> bounces at openjdk.java.net> On Behalf Of Tobias Hartmann
>> Sent: Montag, 2. Dezember 2019 06:57
>> To: Vladimir Ivanov <vladimir.x.ivanov at oracle.com>; hotspot compiler
>> <hotspot-compiler-dev at openjdk.java.net>
>> Subject: Re: [14] RFR(S): 8234617: C1: Incorrect result of field load due to
>> missing narrowing conversion
>>
>> Thanks Vladimir!
>>
>> Best regards,
>> Tobias
>>
>> On 29.11.19 15:19, Vladimir Ivanov wrote:
>>>
>>>> http://cr.openjdk.java.net/~thartmann/8234617/webrev.00/
>>>
>>> Looks good.
>>>
>>> Best regards,
>>> Vladimir Ivanov
>>>
>>>>
>>>> Writing an (integer) value to a boolean, byte, char or short field includes
>> an implicit narrowing
>>>> conversion [1]. With -XX:+EliminateFieldAccess (default), C1 tries to omit
>> field loads by caching
>>>> and reusing the last written value. The problem is that this value is not
>> necessarily converted to
>>>> the field type and we end up using an incorrect value.
>>>>
>>>> For example, for the field store/load in testShort, C1 emits:
>>>>    [...]
>>>>    0x00007f0fc582bd6c:   mov    %dx,0x12(%rsi)
>>>>    0x00007f0fc582bd70:   mov    %rdx,%rax
>>>>    [...]
>>>>
>>>> The field load has been eliminated and the non-converted integer value
>> (%rdx) is returned.
>>>>
>>>> The fix is to emit an explicit conversion to get the correct field value after
>> the write:
>>>>    [...]
>>>>    0x00007ff07982bd6c:   mov    %dx,0x12(%rsi)
>>>>    0x00007ff07982bd70:   movswl %dx,%edx
>>>>    0x00007ff07982bd73:   mov    %rdx,%rax
>>>>    [...]
>>>>
>>>> Thanks,
>>>> Tobias
>>>>
>>>> [1] https://docs.oracle.com/javase/specs/jvms/se13/html/jvms-
>> 6.html#jvms-6.5.putfield
>>>>