[9] RFR(S): 8148490: RegisterSaver::restore_live_registers() fails to restore xmm registers on 32 bit

Mon Feb 1 21:18:40 UTC 2016

Thank you.

Vladimir

On 2/1/16 11:25 AM, Berg, Michael C wrote:
> The new jbs entry is logged as:
>
> https://bugs.openjdk.java.net/browse/JDK-8148786 (for the xml.transform failure)
>
> Regards,
> Michael
>
> -----Original Message-----
> From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com]
> Sent: Friday, January 29, 2016 5:39 PM
> To: Berg, Michael C; Tobias Hartmann
> Cc: hotspot-compiler-dev at openjdk.java.net
> Subject: Re: [9] RFR(S): 8148490: RegisterSaver::restore_live_registers() fails to restore xmm registers on 32 bit
>
> Michael,
>
> Thank you for testing changes.
> Please, file JBS bug for xml.transform problem.
>
> Thanks,
> Vladimir
>
> On 1/29/16 2:28 PM, Berg, Michael C wrote:
>> Tobias/Vladimir:
>>
>> I would change the two asserts to in the 64bit code to make the check clear:
>>
>>         assert(UseAVX > 0, "up to 512bit vectors are supported with EVEX");
>>         assert(MaxVectorSize <= 64, "up to 512bit vectors are supported
>> now");
>>
>> As for testing with the patch applied to hotspot on a current jdk(01-29-16):
>>
>> Windows sde 32-bit: skx - pass, also ran and passed part of
>> specjvm2008 Windows 32-bit: hsw - pass, also ran and passed all of
>> specjvm2008 Windows sde 64-bit: skx - pass, also ran and passed part
>> of specjvm2008 Windows 64-bit: hsw -pass, also ran and passed all of
>> specjvm2008 : caveat Linux on skx: 32-bit - pass, also ran and passed
>> all of specjvm2008 Linux on skx:64-bit - pass, also ran and passed all
>> of specjvm2008
>>
>> We should proceed with checkin in the changelist after the usual testing.
>>
>> Note: The above tests were done with the asserts changed on windows
>> only. The 64bit changes are mostly cosmetic.  It's the change to the additional_frame_bytes that makes it correct, we used equivalent constants in the stack adjustment beforehand, they had not been mapped to the movdqu for the non-vector case for a few iterations on the file.  Early on I did have that code though.
>>
>> Caveat: xml.transform fails with the changelist and without, I checked this against a 12-21-15 built jdk which is 1 month old, so we have a new bug that is causing this app to fail as well (on windows for 64bit) on hsw.
>> I checked recent jbs traffic, the occurrence does not appear to be tracked at this time.
>>
>> -Michael
>>
>> -----Original Message-----
>> From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com]
>> Sent: Friday, January 29, 2016 11:40 AM
>> To: hotspot-compiler-dev at openjdk.java.net
>> Cc: Berg, Michael C
>> Subject: Re: [9] RFR(S): 8148490:
>> RegisterSaver::restore_live_registers() fails to restore xmm registers
>> on 32 bit
>>
>> Tobias, please verify that 64-bit code works correctly.
>> About 32-bit code.
>>
>> Please verify correctness of next asserts:
>>
>>         assert(UseAVX > 0, "512bit vectors are supported only with EVEX");
>>         assert(MaxVectorSize == 64, "only 512bit vectors are supported
>> now");
>>
>> Originally we could have vectors even with only 64bit XMM registers.
>> MaxVectorSize and UseAVX can be set on command line
>> - what happens in such case? No vectorization?
>>
>> May be it is done because we save whole 128bit XMM always. Still MaxVectorSize == 64 condition is strange.
>>
>> Thanks,
>> Vladimir
>>
>> On 1/29/16 6:16 AM, Tobias Hartmann wrote:
>>> Hi,
>>>
>>> please review the following patch:
>>> https://bugs.openjdk.java.net/browse/JDK-8148490
>>> http://cr.openjdk.java.net/~thartmann/8148490/webrev.00/
>>>
>>> RegisterSaver::save_live_registers() and RegisterSaver::restore_live_registers() are used by the safepoint handling code to save and restore registers. The following code is emitted to save and restore XMM/YMM registers on 32 bit:
>>>
>>> Save:
>>>       ...
>>>       0xf34ca12e:	vmovdqu %xmm0,0xb0(%esp)
>>>       0xf34ca137:	vmovdqu %xmm1,0xc0(%esp)
>>>       ...
>>>       0xf34ca16d:	vmovdqu %xmm7,0x120(%esp)
>>>       0xf34ca176:	sub    $0x80,%esp
>>>       0xf34ca17c:	vextractf128 $0x1,%ymm0,(%esp)
>>>       0xf34ca183:	vextractf128 $0x1,%ymm1,0x10(%esp)
>>>       ...
>>>       0xf34ca1b3:	vextractf128 $0x1,%ymm7,0x70(%esp)
>>>       ...
>>>
>>> Restore:
>>>       ...
>>>       0xf34ca202:	vinsertf128 $0x1,(%esp),%ymm0,%ymm0
>>>       0xf34ca209:	vinsertf128 $0x1,0x10(%esp),%ymm1,%ymm1
>>>       ...
>>>       0xf34ca239:	vinsertf128 $0x1,0x70(%esp),%ymm7,%ymm7
>>>       0xf34ca241:	add    $0x80,%esp
>>>       0xf34ca247:	vmovdqu 0x130(%esp),%xmm0
>>>       0xf34ca250:	vmovdqu 0x140(%esp),%xmm1
>>>       ...
>>>       0xf34ca286:	vmovdqu 0x1a0(%esp),%xmm7
>>>       ...
>>>
>>> The stack offsets for the vmovdqu instructions are wrong, causing the XMM registers to contain random values after a safepoint. The problem is that "additional_frame_bytes" is added to the stack offset although the stack pointer is incremented just before:
>>>
>>> 283     __ addptr(rsp, additional_frame_bytes); // Save upper half of YMM registers
>>>
>>> The regression test fails with "Test failed: array[0] = 1973.0 but should be 10.000" because the vectorized loop returns a wrong result.
>>>
>>> I spotted and fixed the following other problems:
>>> - the vmovdqu instructions should be emitted before restoring YMM and
>>> ZMM because they zero the upper part of the XMM registers (i.e.
>>> YMM/ZMM)
>>> - if 'UseAVX > 2' is set/available, we save the ZMM registers as well
>>> but we do not increment 'additional_frame_words' accordingly (we need
>>> another 8*32 bytes of stack space)
>>>
>>> Unfortunately, I don't have access to a CPU with the AVX-512 instruction set to test the "UseAVX > 2" related changes. Michael, could you verify the changes?
>>>
>>> The problems were introduced by the fix for JDK-8142980.
>>>
>>> Thanks,
>>> Tobias
>>>