CR for RFR 8153998

Berg, Michael C michael.c.berg at
Thu Apr 14 23:38:48 UTC 2016


Multiversion copies the post rce'd loop after we check, and we check again before we mark the post loop for mask vector optimization after superword succeeds on the main loop, so we are all good.  The mask version of the post loop is always clean when we apply the optimization.

I tried something like that early on with CountedLoopEnd.
The problem is that the resultant jump has an expected size counter for jcc, so you could not do it during emit.  You would still have to add the side effect much like what I did.  I would be adding a flag to node when we don't need one.  What would like to do then, process via flag or how I do it now?  We would basically be doing it in the same place.


-----Original Message-----
From: Vladimir Kozlov [mailto:vladimir.kozlov at] 
Sent: Thursday, April 14, 2016 4:27 PM
To: Christian Thalinger <christian.thalinger at>; Berg, Michael C <michael.c.berg at>
Cc: hotspot-compiler-dev at
Subject: Re: CR for RFR 8153998

On 4/14/16 3:35 PM, Christian Thalinger wrote:
>> On Apr 14, 2016, at 8:44 AM, Berg, Michael C <michael.c.berg at <mailto:michael.c.berg at>> wrote:
>> Christian,
>> There is but I would have to anchor it via a gpr register, instead I am treating it like nop emits (yet another side effect), with some guidance for placement.
> That’s unfortunate but I understand.  I’m fine with it then.

You can try to generate restore mask on loop exit in mach instruction for CountedLoopEnd node with predicate(n->has_vect_mask_set()). has_vect_mask_set flag should be set in CountedLoopEnd node after creation of CreateMaskI node. Note, CreateMaskI will be only generated for clean counted post loop with on vector iteration - there should not be any other branches there.


>> Regards,
>> Michael
>> *From:*Christian Thalinger [mailto:christian.thalinger at]
>> *Sent:*Thursday, April 14, 2016 11:20 AM *To:*Berg, Michael C 
>> <michael.c.berg at <mailto:michael.c.berg at>>
>> *Cc:*hotspot-compiler-dev at 
>> <mailto:hotspot-compiler-dev at>
>> *Subject:*Re: CR for RFR 8153998
>>     On Apr 13, 2016, at 11:35 AM, Berg, Michael C <michael.c.berg at <mailto:michael.c.berg at>> wrote:
>>     See below for context.
>>     Regards,
>>     Michael
>>     *From:*Christian Thalinger [mailto:christian.thalinger at]
>>     *Sent:*Wednesday, April 13, 2016 2:08 PM
>>     *To:*Berg, Michael C <michael.c.berg at <mailto:michael.c.berg at>>
>>     *Cc:*hotspot-compiler-dev at <mailto:hotspot-compiler-dev at>
>>     *Subject:*Re: CR for RFR 8153998
>>         On Apr 12, 2016, at 8:26 PM, Berg, Michael C <michael.c.berg at <mailto:michael.c.berg at>> wrote:
>>         Hi Folks,
>>         I would like to contribute Programmable SIMD as implemented on multi-versioned post loops. See: the first half of the implementation.
>>         This component delivers mask programmed post loops which execute in a single iteration in place of fixup scalar loops which used to take many iterations to complete work for user loops.
>>         Currently I have enabled this optimization for x86 only, specifically for machines with masked data predication implemented as per fully enabled EVEX targets.  It delivers up to 2x
>>         performance and has been modeled over a large number of loop lengths and forms of loops.
>>         This code was tested as follows(see jbs entry below):
>>         Bug-id:
>>         webrev:
>> +//------------------------------MachMskNode-------------------------
>> ----------
>>     +// Machine function Msk Node
>>     +class MachMskNode : public MachIdealNode {
>>     Does “Msk” mean mask?  Then we should call it MachMaskNode.
>>     <MCB> Ok, that’s easy enough.
>>     Also, I don’t quite understand why we have:
>>     +instruct set_mask(rRegI dst, rRegI src) %{
>>     +  predicate(VM_Version::supports_avx512vl());
>>     +  match(Set dst (MaskCreateI src));
>>     +  effect(TEMP dst);
>>     +  format %{ "createmsk   $dst, $src" %}
>>     +  ins_encode %{
>>     +    __ createmsk($dst$$Register, $src$$Register);
>>     +  %}
>>     but:
>>     +  void MachMskNode::emit(CodeBuffer &cbuf, PhaseRegAlloc*) const 
>> {
>>     +    MacroAssembler _masm(&cbuf);
>>     +    __ restoremsk();
>>     +  }
>>     The reason: Currently k registers or mask registers are not allocated, meaning we have to treat their usage as side effects.
>>     The case with set_mask is to take our remaining iterations as an index and provide a mask used in k1 that is applicable to its post loop.
>>     The subsequent restore, preplaces the default value back into k1.  The set_mask rule is posed in such a way that it ensures that the side effect value will survive optimization.
>>     The restore is fully a side effect with no produced definition in rule space as mask registers are not formal definitions.
>> Hmm.  So, there is no way we can have a RestoreMaskINode?
>>         Thanks,
>>         Michael

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