RFR (XXS) 8234610: MaxVectorSize set wrongly when UseAVX=3 is specified after JDK-8221092

[Viswanathan, Sandhya]

Please find the updated webrev at: http://cr.openjdk.java.net/~sviswanathan/8234610/webrev.01/

JBS: https://bugs.openjdk.java.net/browse/JDK-8234610

Best Regards,
Sandhya

-----Original Message-----
From: hotspot-compiler-dev <hotspot-compiler-dev-bounces at openjdk.java.net> On Behalf Of Viswanathan, Sandhya
Sent: Friday, November 22, 2019 3:59 PM
To: Vladimir Kozlov <vladimir.kozlov at oracle.com>; hotspot-compiler-dev at openjdk.java.net
Subject: RE: RFR (XXS) 8234610: MaxVectorSize set wrongly when UseAVX=3 is specified after JDK-8221092

Hi Vladimir,

I agree the following code could be moved under use_evex:
+    if (FLAG_IS_DEFAULT(UseAVX)) {
+      __ lea(rsi, Address(rbp, in_bytes(VM_Version::std_cpuid1_offset())));
+      __ movl(rax, Address(rsi, 0));
+      __ cmpl(rax, 0x50654);              // If it is Skylake
+      __ jcc(Assembler::equal, legacy_setup);
+    }

I will send the updated patch.

I explained in the other email how we are getting MaxVectorSize as 16 when user specifies UseAVX=3 on Skylake.

Best Regards,
Sandhya

-----Original Message-----
From: hotspot-compiler-dev <hotspot-compiler-dev-bounces at openjdk.java.net> On Behalf Of Vladimir Kozlov
Sent: Thursday, November 21, 2019 6:03 PM
To: hotspot-compiler-dev at openjdk.java.net
Subject: Re: RFR (XXS) 8234610: MaxVectorSize set wrongly when UseAVX=3 is specified after JDK-8221092

Hi Sandhya,

I think you should put cpuid code added by 8221092 under if (use_evex) checks because if user specified UseAVX=2 the code under (use_evex) will not be executed anyway. Or I am missing something.

I did not get why you said MaxVectorSize is being wrongly set to 16 bytes. It should 32 because it will set UseAVX=1 in current code.

Thanks,
Vladimir

On 11/21/19 5:27 PM, Viswanathan, Sandhya wrote:
> On Skylake platform the JVM by default sets the UseAVX level to 2 and accordingly sets MaxVectorSize to 32 bytes as per JDK-8221092<https://bugs.openjdk.java.net/browse/JDK-8221092>.
> 
> When the user explicitly wants to use AVX3 on Skylake platform, they need to invoke the JVM with -XX:UseAVX=3 command line argument.
> This should automatically result in MaxVectorSize being set to 64 bytes.
> 
> However post JDK-8221092<https://bugs.openjdk.java.net/browse/JDK-8221092>, when -XX:UseAVX=3 is given on command line, the MaxVectorSize is being wrongly set to 16 bytes.
> I have a patch which fixes the issue.
> 
> JBS: https://bugs.openjdk.java.net/browse/JDK-8234610
> Webrev: http://cr.openjdk.java.net/~sviswanathan/8234610/webrev.00/
> 
> Please review and approve.
> 
> Best Regards,
> Sandhya
> 
>