RFR (XS): 8215888: Register to register spill may use AVX 512 move instruction on unsupported platform

[Viswanathan, Sandhya]

Hi Vladimir,

Please find the updated webrev with your comments incorporated at:

http://cr.openjdk.java.net/~sviswanathan/8215888/webrev.01/

The jtreg compiler tests continue to pass on Haswell and SKX with this updated webrev.

Best Regards,
Sandhya


-----Original Message-----
From: Vladimir Ivanov [mailto:vladimir.x.ivanov at oracle.com] 
Sent: Friday, December 21, 2018 12:00 PM
To: Viswanathan, Sandhya <sandhya.viswanathan at intel.com>; hotspot compiler <hotspot-compiler-dev at openjdk.java.net>; vladimir.kozlov at oracle.com
Subject: Re: RFR (XS): 8215888: Register to register spill may use AVX 512 move instruction on unsupported platform

Sandhya,

I'd prefer to see the check inverted:

     if (UseAVX > 2 && !VM_Version::supports_avx512vl()) {
       int vector_len = 2;
       __ evmovdquq($dst$$XMMRegister, $src$$XMMRegister, vector_len);
     } else {
       __ movdqu($dst$$XMMRegister, $src$$XMMRegister);
     }

It looks easier to read considering the code around is full of "UseAVX > 2" checks.

By coincidence I was debugging the very same bug today and at first I didn't notice the problem with "UseAVX < 2" misreading it as "UseAVX > 2".

Otherwise, looks good.

Best regards,
Vladimir Ivanov

On 21/12/2018 11:44, Viswanathan, Sandhya wrote:
> Hi All,
> 
> We noticed that the register to register moves in x86.ad file attempt 
> to generate emovdqu when UseAVX==2.
> 
> The instruction emovdquq is only supported on platforms where UseAVX > 
> 2 (AVX 512).
> 
> The following rules in x86.ad file need to be corrected:
> 
> MoveVecX2Leg
> 
> MoveLeg2VecX
> 
> MoveVecY2Leg
> 
> MoveLeg2VecY
> 
> The above move rules when activated through register allocator could 
> result in illegal instruction exception.
> 
> Bug:
> 
> https://bugs.openjdk.java.net/browse/JDK-8215888
> 
> This bug affects versions 11.0.2, 12 and the mainline.
> 
> Webrev for jdk mainline:
> 
> http://cr.openjdk.java.net/~sviswanathan/8215888/webrev.00/
> 
> This webrev passes jtreg compiler tests on Haswell and SKX.
> 
> Best Regards,
> 
> Sandhya
>