Eclipse OMR Architecture, 1 Aug 2018

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From YouTube: OMR Compiler Architecture Meeting 20180801

Description

This Compiler Architecture meeting discussed adding new IL opcodes for read barriers and FMA operations.

Please add any comments/questions to the GitHub agenda issue: https://github.com/eclipse/omr/issues/2817

A

Okay, welcome everyone to this week's compiler architecture meeting. So today we have.

B

B

Into the entire process, some tradition around us so for some.

A

In an issue you then created in issue 2012 and other.

C

So we're proposing to add the power of code of two recent development items. One of them is for debugging purpose to report all the field, access to VM and the other one is for pause list GC, where, whenever we load and dressed hypotheses people are going to cause to the end, to a success of whether if the object, the object is were in mood and so those in in both case, the field load would have side effect. So we we want to create new op codes to represent both the load value and the side effects.

C

With the current current designs that we would have a grid bar and Jerry's bar I group refers for a load from attitude and with bar I is for load from Natick fields and different field types with have. If we find.

C

The article uncle's would be similar to alcohol and will be I mean under our feet up so yeah. That's our initial.

D

Discussion on longer.

D

You have some idea of exactly what is going to be done when that's evaluated.

C

D

Do the evaluations look like on.

C

It mean value in the sequence: generative yeah. What.

D

C

You what would.

D

C

In in case of in some recent publicity, it would be two extra instruction to do a bunch edge to check if the object is in the valid G Val HD region and if not called to the DM CalPERS and full report for the dependent purpose. For the other items for the father, we will call every time we do a few to read. We would call out to VM helper to report the read and then to the normal load and come back.

C

Here those cases like with my holiday amount.

D

So it's possible that you have to do both like one or the other or both right. There.

C

Are two two different items? It's.

D

One up, coders and.

C

One is not it's: uh both of them use a rebar.

D

You show you what I mean what I'm asking is. You would there's a situation where you could be using pauses, PCM and the debugger at the same time. I. Could you have to do around check and the load and then notify the VM? No.

C

Debug I, don't think we'll be turning always.

B

C

E

Garbage collection move shouldn't be dependent on debuggable.

C

E

Spain Rosie's we have a pre barrier, is implemented, but we're not using Iowa or we do a reduction of Cochin time. There's no problem. What's 50 buck with cranes, Gavin Johnny's, I.

C

E

In general, it's useful for GT, just like we have right barriers on or I think, there's Alex mentioned previously from the GC team on open j9, but there's other flavors of garbage collections, which do it by Reed barriers from the middle, especially dictate in Egypt today. Similarly, to how we have card marking for right there, yours.

E

There's other GT policies that currently is going exist, at least an open j9 which could make use of readers. If we have I suppose GC is just one of them and.

C

I guess the answer is yes. Yes, so.

E

There's a sudden, I I, don't think the pile of code itself should have any side effects. You should just feel if you look at any other regular load. As far as the optimizer kids.

C

But for field work case, the other would want to know that all the theory, regional click.

E

C

Cannot comment, or so.

E

You cannot comment yeah.

C

E

That's going to be a problem.

D

Only if the debugger is really so, the behavior will change a little bit right on whether it has a side effect or not. It sounds like as they you don't want to propose with chase me, but you do want to trick the debuggers yeah.

C

So cosmas GC, we were thinking only transforms a note to rebar at a lower tree so that normal optimizations they will kick in for the load.

E

That sounds on Orthodox, okay, what's the point of having the il, if you're just going to reduce it to something up cogent time loop, you can reduce it to a call, for example, special calls barrier.

E

But the whole point of having the il is for that the optimizer does care about it and can do stuff. It I.

A

Guess you could make that argument for some of the other guy up code as well? Why do we have want to get lowered in the eye? For example, like multi new array, we.

F

Can focus over that and then do a call that.

E

Should be a causal I, don't a we should introduce these files, but the whole compiler should care about they're, really Italian coaching you're kind of trying to represent them intrinsic at that point in here, after optimization.

E

They need productive in oil that.

D

An argument for read over here.

A

E

Sets an argument idealization and.

A

Right there yourself right.

E

A

E

Caught it, the optimizer intrigued by barriers today, so quickly, a sports, the.

F

Right hand, side is a new for the moment mark the right bar. You don't need to do it in approving in this game, when there's a class of optimization that happens and value companies or or right to our situation,.

A

So extra to your question: are there any optimizations that could apply to green barriers of this kind? Like other example, are there any opportunities for eliminating these pre barriers.

D

By the optimizer you can proves properties.

D

Depend on if the debugger is funny or not if the family debugger is running, you want to be conservative or change anything, but the read barrier is for all those cheesy or other less restrictive purpose, probably one to do something.

A

And in the case of the debugger, where you need to report field accesses to the VM that that also include rights.

C

A

If you write to that field, you also have to report them yeah. Would you use this remember no.

C

That another topic we are still considering whether we need to add a write barrier of code for each type or we can just use the sort of code.

C

Because for right, the store would already have anything, so it is in wouldn't change or light or sewer code prefer.

C

It is a bit different from a normal.

D

Door, the store the behavior you want, you don't generate different trees but valuation time somebody's cooked check if field is being watched, yeah and then so. Ok, yeah.

C

And that also there's also problems with that, because samosa alt that normally we can do a store, cannot sit down in this case, so that implies we might need to change some. Why is that case?.

D

Yeah, what I don't.

E

D

Is it it ever since we're watching field.

C

If a user Villa fell over oh cool next morning, her the field after then, we want to accent.

E

Why would that matter if what, if the JIT sauce or why would that, whether you need.

D

People or not other compilers,.

E

If you want to debug optimized code, you.

D

Have to live with the fact that maybe they disappear or change that often like it will just reason. I asked is the java: let you do that, or did you have a say that it something is being watched, it has to changed in any way that would a malicious.

F

C

The last conversation with the M team I was told that we want to know the original. We that's right.

E

Then you can compile with no optimizations.

E

Happy I mean because you can't put spline il to behave differently based on text when.

F

The property is have to be the same, regardless of.

C

F

Modi array mm-hmm.

C

F

That you generate conceivably could be different, although that needs discussion, but depending on the different moon. But the properties better be saying right, like.

E

It's always a trade.

F

Off or not or as a different I.

F

Think you are setting, it has to be a treat on have a strap-on if the rest will be earliest. Certainly if allowing commenting of the operating circumstance, I'll correct the Faro.

C

Provocation detail all spend.

F

One else who wants to reuse this on food better be willing to adhere to those constraints.

F

If you want a read bar that is a floating read bar, not a treetop one. If you wanted some other aliasing or.

D

You wanted it to be.

F

Comment, this is not the awkward for you. Another way of saying can.

A

The children up can the low the underlying low of a barrier because.

C

There were no load, and so.

A

Like in your case, you can happen better next well, rebar I, with an a-level end, rinconete able that.

C

An old can we can be common good.

A

Town to get this model or because it's it's, it's child yeah.

C

Because right, it's an auto, it's nota! You.

E

C

Hear you, you have a arrow.

E

X 3 bar I, that implies you can comment. There is also to load bars, I'm reading. Is that what you intended or.

C

That one is like for compressor ax and we will have a different treat halls, but can reference to the same town.

C

To the same, let me.

C

D

Allow comedy upload: doesn't that kind of defeat the purpose of the root barrier, because what if somebody wants to use the read barrier to catch, to change the value before it's read? If you allow commenting as a not allow a little to happen earlier and you're, just using the value and yeah.

E

I'm not sure what what this for this loving commenting of loads, that our readers, hmm you have to have those every common to use. The results treat.

F

E

Howdy actually.

F

Call it downwards, because I couldn't be coming up.

E

What do you mean coming up.

D

With the load happens above and the great barrier, child is just the reference to previously. Okay.

E

D

Okay, I understand yeah.

D

Just be barrier to catch the little before in my change it in the debugger thing, yeah the.

E

Child of the reader should never be common. I was just different.

F

Than what we were of them sit in some written unless hi I'm sure we have something clear whether the rebar one is the read bars. Child Lily I, think we've nailed that down in this meeting I think the read bars in the place, the load, whatever the original Lord's children child was not.

C

F

The child of this rebar north of me factor M rather original.

B

C

F

C

F

Laws on the original, no dyes, probably what's going to be the same riff on this reef, alright.

F

Interesting retinol.

E

Ism and being better.

F

Reeling from Penelope clinical record.

F

A special gameplay.

A

Just out of curiosity, are there any other up codes where we strictly disallow commenting in same way call call okay, yeah.

F

News, because you have to nuevo yeah allocation is stuff.

B

Right: okay, I.

F

Think that was kind of the model that he's looking at right.

D

F

You're no commoning comment isn't quite put no commenting as I.

E

Was raised before boys.

F

Anchored to a treat, that's always anchor to a treat. All that kind of like saying it's Raph count will be too, but never more than two. They were less than two. Never more than this won't consider it there's one yeah, there's a tree top anchor. That's not a real consumer, though there's a real consumer who consumes it yeah that count becomes to yes and never increases.

E

Be here so why can't you come in at that point further down.

F

Because of one of the use cases she talked about.

E

You Reza's value of the field and I started into a local, so I would meet a rebar on the bead of the field, but then I start into local and then use the local pythons, so wanna be forced to use the.

F

Tom's, like fishin.

E

Yes, nobody wants. That was wrong with that I read a value for the field that did whatever I needed to to handle. That I think that take what we wanted to prevent was two Reapers being fused into one, because we're reading the same sentence.

F

We've been talking, probably don't, think it stinked calmly propagate on all right.

F

Fundamentally, she's in a mode where performance, equal, almost isn't at the top of or perilous at.

E

Least for the debug lady or the debunking.

F

E

You just disable hittin all your oxygen too long I mean you can't try to optimize your debugging. If you don't want to comment, no reason, people come along and complain it with us. Cool things are when I turn this over on. You can't go too far on that.

F

Sure it's intended to be used in full in the gel and javis full speed, debug one.

A

Of our two excuse.

F

E

F

Have another nice thing unit is in.

E

Production today, which is also GC on on dead, yes and our reads- behave exactly like every other read in the compiler, except that the very first read has to appear under a tree top anchor. That's it that's the only restriction, so I, don't understand why you would have to prevent common email. Also reads: area like our reach can have rep count that you want so follow along as the very first one appears on our tree top. That ensures that our reads very evaluator will generate the correct hardware, repair your sequence.

E

So guess the question is in the debug scenario: did you want kids code necessarily produce the same Stonefield, the event interpreter women right and if that's the case, I mean we should disable optimizations rather than limit what the spec pretty il is. That seems like a knob on the performance versus observability spectrum. I, think you could imagine people who would want to see every read and you know screw.

C

E

Don't want you to eliminate field reads and you could imagine. Other people are like well I just want to know when this thing got read and I, don't care.

C

E

I do that optimization rather than a patient yeah. That's where I'm going with it right, like it's kind of a you, don't really know what you want to see all the reads: stable, local 50 you'll have them all everything will be read very problem.

A

But it's not giving back a lot of the performance that we were putting it.

F

In so you can turn off local TV and you're right. All the ordering would be exactly how it needs to be, but that's not the only way you can achieve done in trees. I mean local TV does local copy propagation as well as local khamenei, just they're tough. You could continue to do local copy propagation.

F

Just turn off comments. Sure.

E

Yeah I'm just saying in general it it's an optimization, then we turned out if you want that desired effect, depending different specifications for the ayah, which depends on right.

F

Why was there a different resolution also.

E

There is in one scenario you are coming in and yell when you don't, how do you define Gail repetition is, does the opcode requires you would not comment or not I'll be proper year or whatever, or is that just an option or trick, and it's actually an option? Whatever scenario you imagine, your VM work.

E

Why can't a different VN, maybe a different VM I, don't know your Python. If we don't need to report, everything will feel watch just as one that's the jitters.

E

This case sure for those bmz would enable local, 50 and quiet it didn't seem so much a property, the opcode assaults by property, of what I think, what we want to represent is the very first time you're reading it you're accessing memory, and you need to do something after you've read it and it's in a register use it. However, you want that's totally fine you're, just moving a value around you're, not loading anything from memory in.

D

The in the Javits debug cane, how does somebody set a watch? What are they setting and watch on? So they just say: I want to watch this field, yeah.

C

D

To be notified of all read.

C

E

That becomes the nose or point as well. Oh yeah,.

C

So so we might start from normal hospitable and few watches turn down. We need to. Oh s, are we compel?

C

F

You get clarity on the specification if you missed one of these little three allowed to miss commonly how liberal is the specification in Africa.

C

Gag, that's not allowed yeah. Okay, you can.

D

Use, you think, interpret every good, oh yeah yeah. They never limited.

F

But might be something poking yeah, yeah I, don't want to add it a lot discussion. Why is it.

D

Not allowed it was specified somewhere, I, don't bump.

E

Answer goes back to the MT, either nothing like good answer or that it's some Java centric requirement. That's not a good enough answer. How's the ball posted behaving Omar. It's an argument to say that off code needs to support what open j9 needs with this whole food, but it doesn't necessarily employ the health code has to do exactly that in.

F

A specification you know.

E

F

The there's argument that one has to adhere to what the interpreter does, because different argument that one has to adhere to the spec is right. So if the spec gives us wiggle room, wiggle room that the interpreter doesn't take advantage on, doesn't mean we shouldn't take advantage of it. So.

C

F

E

It's still worth digging into a.

F

Still means that's.

E

One interpreter and one specification or more directly, no more off collect. There is an old.

F

E

Interpreter or specification, the determines what we have.

F

E

F

An interesting description of the sauce code right. What is it? Yes, that's actually one of the.

E

Things that I think is missing from distance like words, so I'll just refer, one finger or I think.

B

If words, it is, you are crazy.

E

What are its properties serrated the whole floor for crazy on the difficulty with had without having a read barrier. Opcode was that we were kind of mimicking it by anchoring the first load at Cochin time and the reason we had to do this was because a normal load appear anywhere the first time um and in code generator we have tons of sequences, wait, wait pattern match, you know some tree sequence or with full things into memory, references, etc, stuff that you can't do on the instruction which actually needs to generate the read barrier.

E

um So we have to know exactly the first time we feel alone. We can't use like load and add, does that flavor of instruction doesn't exist for a reader or a particular architecture. Also, they need to be anchored in a treetop so that we can recognize. Okay, I need to generate a very simple vanilla, read, barrier load and then, after that, in common entity, whatever you want it, but as long as the very first one appears underneath the garden load instruction for architecture that was kind of a big difficulty.

E

So did you say that you accomplished that placing a pass just before the code generator in the optimization that goes by and finds the first load and anchors it yeah yeah I'm, happy like that.

F

They're doing that transformation in the aisle and you still have other complexities in the evaluator or that passed before you.

C

F

Children walks the IL anchors first load currents of the load of your traitor. That's fall on me.

E

Has been a means, we have to disable a couple of other optimizations. We win for example, or are not yet especially I hold up, and my index and base are the same. It's a multiplication by two, so I just folded into that those types of all um all those have to be disabled for read, barriers, there's a whole bunch of cases in the coaching or we'd say: okay. Are we generating read barriers? Is this one of these special ones? Don't do this all right away, which would be a lot easier?

E

We had an actual read barrier up code now, I, don't know what other things you might be able to do on the optimizer side. So.

F

For sounds like your requirement would be, if you want the opcode, you want authors to be anchored under crate on in.

E

Other words otherwise behave.

F

E

Other, like alone, is.

F

E

Carefully time, yeah and shouldn't yeah there's no reason why the patient care, just the value, doesn't give use whatever you have to do associate with that local and use it all USB. All we care about is we need to very first time. We load this thing from memory right and do something about it. So, even just within Java we have the argument that which is just pop code needs to support a variety of use cases. There's a complex propagation, similar to right.

E

There, I mean right, there is more or less one should behave like a normal store, except there appears on their treetop, and you know it's do something special with it in any one. Your VM yeah.

F

So, even after that discussion comes back to the same point, are you allowed to common this or known people the answers yeah and keep pretty much habit, Marja little? Something else that we haven't heard about yet, but pretty much have a consistent story.

E

Across the debug and.

F

Positives be a treat on.

E

Doesn't local in I took locals? You see, there's an extension as an extension point, at least at simmering, for something we create something on the sim reps find out. Can I comment this thing um so I can't under the post, P debug or whatever I just create an extension point in open j9 and to say both on your debug? No, he can't come in this load.

F

Clients, probably how implement.

F

Because I don't think.

E

There's just and I hate Romney vacancy dir off levels and turned off at that Omar level. You should do it at the open, G, nine lovely! That's what you need.

C

E

That assumes that it's the same rest. That knows the answer to the question.

F

Right which, in this case and it does but.

E

Maybe not in our stills uh I'm a I'm, a user who wants to be the reads that actually happen where I want to do. I want to be able to see the events between reads that actually are done by my program, if it just optimizes to reads into one I: don't care I just want to be the ones that have actually done. That's not a stim ref answer, first, a although it could be configured, though you could have a simmer as the computers, its building x-ray, guys.

F

On calm, calm want to feed all the things that actually I guess. The question for me would be: is there if it's going to be the sim ref answering.

E

Yay or nay, is there a case where only some sim reps would answer? Yes, if that's true, then that's already out for the sim rest, knowing I mean.

B

If you can only logs.

E

It's always one or the other than that's an argument to me that.

F

Maybe something else's may.

E

In principle, against.

F

At the same point, that very magining.

B

F

Decides based on some rest who decide based on the note respect, then it does have all the influence pain. No thanks in this case, yep I.

E

Think your recent winters and like this for some parks, decimal commenting in open, G, nine or we didn't want to do local CSD on a particular, no with particular side effects, which is exactly what we want.

C

Yeah, it's just so Corey and you're just returned no.

C

That also giving tonight almost feel the reef as well, so we might need to change.

C

B

You husband intervention point yeah, oh.

C

That's true yeah, yes,.

F

Puma done copy complicated, yeah.

C

Is that's the only two all.

F

C

Yeah any other.

F

C

I should be worried about here.

F

Ian look I.

F

Think this discussion, good one that ended up in let's try to avoid.

C

F

Commenting through the optimizer, rather than anything on the off our code, allows company or doesn't say anything about, doesn't forbid calm.

F

Even our explore, you go back in like okay.

A

Together, the request was to perhaps.

A

Document, the actual semantics that you have in mind for the review job code so.

E

We have a I remember. Last time we met for aisle specifications. Do we have any sort of template of how we want these things? To look. This would be a perfect I was actually just thinking which huge like.

A

Three seconds ago, he was talking about that this, that who should actually come up the template or these kinds of things in the future and there's.

E

No better time next.

A

Information, you need to be able to provide for us to have this kind of discussion. I'll take that is it.

E

In Turkish, so if you do to make this thing um combinable on what are the implications on the rest of the optimizer which queries or things like? Oh, is this ping, a load Aloha? um Those places need to be switched to kind of acting on property, rather than my Allah codes. I would imagine still convey all relations that are specifically looking for a rank of code. Yes, the bowl need to change.

B

F

If there's no taco a load on.

E

You a tree bar I, think you shouldn't be LLL die or yes, a right bar I should be a property of all those of us that specific or.

B

C

E

But I actually editions that we get checked. Is this.

C

E

A load of an address or something okay, there's a load. This is build an address that an interrupt those those kinds of properties.

C

E

That's great, but better still a lot of code that I'm specifically looking for an opcode value and.

C

E

Information trip on these and those should be changed, look at properties not as Phillip says, to or or it's a rebar I. Yes, because of you there with.

E

Other things that are asses just keep descending or yeah.

A

So they're also going to provide the very least or each feel type that we have right now. Yes,.

A

B

V and spa yeah.

C

C

E

Complier there's to see that when she disappear, I have great hope and the alias death. Where does the array access fit in we've got you've got class, not a future indirect object. We're just little put an array load.

E

You need to remember that. Well,.

C

Partly key yes,.

F

Peters, for both, you need to try being ripped.

D

Only can you watch.

C

D

Of elements of an array now we're being asked for an element of an array: yes, okay, have.

C

E

About that, one I was more concerned about the GC, oh yeah, where you're loading an object, reference out of an array, that's kind of like a place where you might either be barrier.

F

If you're doing yeah.

C

F

Not just a problem in animating it in the Dom, the off chords use are the same. The.

E

Other you're doing.

F

In the race, until.

E

They have different different numbers of children or to be oh, we unified that point making.

F

Two of them, the.

E

Same they look the same, whether it's a field or an array.

C

E

And in Direction off something one.

F

Days, it's an object.

E

You locate very.

F

Actively in a lab or may I add on earth or very access, just an object. Yes, either case it's the hackers.

E

That mole, that a GC read barrier is going to need in order to update.

E

Potentially update, repeat I'm just worried that GC might want have a owning object, as well as the address of the element.

F

How do you guys deal with it currently with a lowered opcode.

E

We might not even know what the parent object is. The GC doesn't need to know it just needs to know the address of the right thing. That's being updated, yeah I mean it comes in through a parameter and it's an array element. Yes, you can never know.

D

I need specific instruction. Is there any reason why this would have to be evaluated in all of the code generators as opposed to some point before turning it into whoever whatever needs to be done? The call to authority, and then conventional load is the way we do things that I was sweet, that write barriers, go all the way to code generator and everybody more or less plus the same thing we repeated five times there any need to kind of go down that path.

C

Generally, before.

D

Code generator, could you generate a call.

D

That way, you wouldn't need any potential. You wouldn't need any Co generator changes. It would just work across three or four five and ago generators.

C

We have about sagar pays.

C

Always you need to see me to do some checking both to check in developers. We need to check something to see if we do watch that.

C

Call be a mouse too important.

B

D

Relevant for structures, gyrated, simpler ops, coated areas, already support express what you want done without having to do. However, you don't have to change any of the cogent.

C

4500, therefore, read.

D

A bit check of the steel being watched that, theoretically usually.

C

On train static and you can.

E

Do it a revolver trains or something.

D

Okay, yeah just the complexity is that going to have. Is that going to be harder for some I'm version, a technical reason which is possible.

B

E

Prefer coffee, it's right! That.

B

Effort anything to people what you want to do with I think.

E

You do this on your VM right. Yes, some cases impede Java or preventing that reduction, and it also might be different for architecture depending on how you want these three bears case.

E

I think we should be reducing anything at the home. Our level, though, although it's been principal already.

F

We're already just using loads anyways.

E

So the Breitbart could just eat lower to whatever thing it is the year. Does new code generators team office to generate an uncharted load instruction.

A

That I could Evi I'd, really love the most and a chair, especially if you fellows right under a tree top yeah.

E

We've had a matching a load, though.

A

You know I got it plugged in back. There.

E

My argument against his his proposal, which was lowering because the rivers yeah.

E

I'd wondered it, but people eat sort of solve that problem. The way it not be the way we want to do it like you're alone,.

F

So no bigger action for you from the point of view of the cogent is that, by virtue of using a separate off code in lock code, it breaks all existing pattern match. That's one of the attractions. Why do you want to be the rebar? Because.

E

I guarantee that at a treetop level, I know it's a reed barrier and I know the thing under it is what I want, in this case, an object and generates an appropriate instruction for that um without having patter, Magica plus Raja I have to consider everything understand what more shapes the thing can appear under any part on cable is very.

F

Easy then I thought yes, I.

B

F

Rate of any first, he was bully her to repeat quick.

E

And matching everything medicine in anyway. They sink that fear they're, trying to avoid that by having the aisle specification guarantees that the various tools.

F

E

F

Mandating to find the first occurrence of what tree you want in three order in visiting like using a visit can't like approach time. Ii visit alone is when you know pattern matching visit, then you picked up anchor it on retreat on depends near one. Why I need to batten anything to incur, but.

E

Can all have the voltage of the code is more complicated than that.

F

A

Really just pulling on something that you with said earlier about, um perhaps in the very near future needs is for rights as well um from a symmetry perspective. I think we'd be nice to actually all.

C

A

You can fix it explicit, it's read and write, but if there's some kind of a generic access barrier that we could come up with instead think of it.

A

Underneath generic, so instead as I having 9 times 2, so 18 read barriers and then.

B

Speaking for that 18 barriers, okay,.

E

Yes, let's are the rectory reused today, the type of the riparian for shell and.

D

The right pair house difference coming on the keyboard. Some of them wants for the rights of the more after the right, yeah.

B

F

A

I'm just trying to we can inject some symmetry, and it is because one of the other options you were saying is that you don't even need to have a an explicit barrier for stores, beifong's test.

E

Nordia president, here right, we already have load off, goes and store I'll close the term, but they're only differences.

E

Spying on those no pushing together or rebar or but every then you want to have right. There goes not.

B

Just fold into the store, like I, think what you're saying it's.

A

One possible: u of m-flint, do that if you want to expose to this reason, that's.

B

Fine I guess I.

F

Think we're not trouble defining what knock on does even without a generalization, okay. Well, so the original rain barrel. What is it you is? One of the questions are still out there.

A

Exaggerating to prove.

F

It sounds like a slippery slope where you can then start making the same argument. Maybe that's what marked the thing, but if you don't need a rebar on a right bar, do you need a loan in a store? Why not just have one thing that represents the lip door, but.

A

Different I'm, not at rebuilding, that is precisely.

B

Identity, children by.

F

Story, so you need extra tiles, so it lists so I'm. Just saying that's a a deep question that we're probably will end in the answer. Yes, we do want to distinguish between loads and stores. Oh yes, we do want to just reread bars and write bars. Okay, it's valid question to a hospital effort to be far off numbers down. We should do it a talk, but sure hope it doesn't end where I. Otherwise. This.

E

Is 200 awkward.

F

F

I know does that we dramatically.

A

Simplify our migration talking about this, do what it want this you. What I want all code? Three um then I think is well I. Guess you can even as part of how we want to. How do we want people to request new wyoweb codes to the feature link part ization part of the thing.

B

You need to think about.

A

It test, especially in the context our how we're going to test involve codes so that.

B

A

Whatever semantics come up with three barrier, we can actually test with a bill test or a color test.

F

To make sure that.

A

F

What we want it to do, yeah at least properties like- is it actually under a Klingon as it swung down? So we have validation is another one. Yes, very property. We are so anxious to see. It preserves earth treatment.

B

All right, um a.

A

More discussion.

E

On that one, what's the default implementation, we just not the right barriers to load.

E

What is it possible? Evaluator, no harm or Praetorian wonderful map.

A

Into its surface load.

A

And then objects will provide their own evaluator right. The evaluator I can.

E

Elegantly, which mean.

A

I've ever even.

E

Want to do we supply a right barrier, evaluators, no, more good, quick, I, just never.

A

Looked I'm sure, there's a big $7.

E

A

Think that's one of the things gets swapped in the table. The evaluator table. We.

B

Need a better role, we need a.

D

E

B

For that battle, room.

B

A

Yes, great bumpy and pedaled again.

B

A

Write in a candy without later.

B

A

D

It's probably okay, somebody ended up writing a touch. That is that they would override that to do with log call a function in their test framework, so I can use that to validate doing what at one, if they don't want to use it for actual purpose. Ism do the same. I reckon just for here.

E

Is that also begs the question? How would you generate these in the first place, so that is that a front-end tech thing Lord? Is that a configuration Omar saying how to generate read, bears.

E

Up here, shouldn't mostly creative aspect, read messes on.

E

There, like crate load, basically could use return bar I would avoid somebody manufacturing load of there is not realizing they had to make it to every bar right.

A

The time that subtle, what do we use create load for non? If you don't want to do this for each box right, so we'll done it instead, XO we access something off over a VM thread or some.

C

A

Of you know, data cells must be smurfing just and then you can still work around that, but you can create your own. No good I was using create low right. Yes, yeah.

F

So, top of pink a while, yes, like.

A

Is that how you were thinking of doing this timing like not explicitly going and creating a rebar but letting the existing framework say? Oh I know your reload of the heap, so I need to give you into something different back.

C

No, it's not what I'm thinking it's not that smart, it's just in Iowa jin-woo will know. If we are accessing on people, then they'll query, query! Well, content to be.

D

Generated all field.

C

E

We shouldn't limit the output in Omar.

E

So your gluten was, we shouldn't. We shouldn't implement the evaluator. There should be no default evaluator for a repair, there's no way to generate it. No more. They shouldn't be at people at validation,.

C

E

I write a read barrier to build their service you're going to make the implement the evaluator fork. You can map it to the Omar's flow devalue, no problem.

E

F

Downside about having an evaluator.

E

In I guess we don't know what it does right.

B

F

E

Because I don't know some VM, for example, Java only wanna go repairs on heap objects, I, don't know if I'm inflating, GCC ml right every read as a matter of it or not, but it along a field. Watch on an abstract allocated objects shouldn't like a puzzle. Gc implementations didn't sink into home or at that point become part of the rebar like.

E

If it's some other home or consumer wants to use a puzzle. Cc technology and the evaluators exist in Omar I, don't know what they do right now, but shouldn't that be an option available which would imply weep one valuators and more for.

E

Star, it won't take me very long right or.

D

B

You do that in what? If there are no.

D

Jobs actually provide other things to allow somebody to get a watch actually working yeah. The watch sure are you in love, you favorite. They would even have to tell you what do I call.

E

That seems like a very fun to need to thing. I mean for the budget. Just goes back to the. What does this all code, yeah.

A

Different yeah, if all you want to be able to do with some kind of platform specific function, when you see one of these right barriers for the first time, whatever.

C

A

Happens to be evenin Omar. We could map that to something that that does something that we can use to text right, I, don't normally print out the value or whatever it is you're. Reading I.

E

Mean presumably the lowest bar here is that the rebar is a load of the things little intro, so either you're, not in the TCD things that you want or you're, not watching fields or whatever it has to be able to load. So it seems like a good people to me, and we should provide is more.

E

Then we can generate tests which can run the I evaluate a validator which validates that the the read bar nodes are being handled appropriately throughout the optimizer at all more and they and functionally they do actually load a value right, which is what I are supposed to do at a minimum right seems to me a better default than unimplemented if, as long as we specified the feed barrier to be strict subset of what the properties of a load are true, which is DVD plenty, the specification difference exactly.

A

Okay, any more discussion on.

E

A

In next steps, um so I guess document what this thing does.

A

I think you were going to look into whether or not some of the constraints could be relaxed. I mean I, guess this is. This is going to get into the semantics of what this does right. So you need to kind of activate it to into that, and I need to come up with sort of a template for what information needs to be provided for, proposing a new pile.

B

A

I think that, hopefully you could follow some of that.

C

A

This, like super urgent for you, like you, have to get this just.

C

Wondering what your.

A

Expectation is for.

C

Emp max how about it is think of me: okay,.

A

I'm, just if you need something like by Friday know.

C

One thing, but.

A

If it another night right, okay, so testing and another consideration as well so.

D

When we're going to have.

A

This two or more so think about how we're going to test this for the various data types that's static and it for direct and indirect as well thing.

E

Modifying all the locations and the optimizer that care about yep, the specific aisle load needs to be changed to outcome properties instead.

A

All right, okay, um so that took longer.

C

A

I had expected, it would take so the other one is I'm, really hoping we can get through it in 20 minutes, but so it is a proposal to add IAP codes for actually going to time back to the 20 minutes enemies. So it doesn't. We can't conclude the discussion. Then we have to carry it on some other time, but the proposal is spring. It up here.

D

A

I'm going to speak on behalf of shabam who's, so one of the things that he's working on at the moment is adding support for F mas into into Omar. This isn't necessarily for languages, but it's not for languages like Java it's for, but there are uses of this in Java, and one of the things that you like to do is to add new scalar FMA up codes to Omar and the denied call those scalars because they're already our vector FM a pileup codes in Omar of all things, which is.

B

A

Which I, don't think are actually used or in any way shape or form, but they're part of those part of our API, so so anyways. The the proposals that these eight new aisle op codes, where they could potentially be generated, is actually during actually doing simplification, so we can actually recognize you're doing some kind of an idiom recognition pattern where it can discover these sorts of operations and then turn them into an OP code like this.

A

It can also do further simplification of these op codes as well, and, do you know value propagation or what happens folding as well? The semantics of these probably need to get specified a little bit more carefully. I think you've got the arithmetic operation here, but we may need to go a little bit deeper in terms of specifying what exactly it is of the semantics are going to be.

A

We had a discussion about a month ago on floating-point semantics in omr and really the answer that came out of that discussion was that we need to have a means, and we don't have this yet a means to actually delegate some kind of a language environment to ask it. What the proper floating-point semantics are in that environment.

A

We have the Aris end class the moment, but that may not that mean that may give surprising answers in some contexts that.

A

We that we need to colmar shouldn't be bent I'm sure when try to say gif Omar may get surprising answers that a particular language runtime may not may not want to give. So why did I say that well to define the actual semantics of these op codes if we're folding and then that kind of thing I think that we need to be able to provide some non surprising means of folding these kinds of operations, so.

A

Yeah, so the idea here then, is introduced. The dialogue codes have them generated either by a language front-end if it can or actually generated within the optimizer.

A

The back ends would then go and map these, ideally to two hardware: instructions, even if they're not necessarily supported, they could be implemented using instructions as well like Tomica, individual instructions, I'm, not sure why you would do that, but that's not the possibility or for breaking these apart and I. Would imagine these going to be creating some test cases as well to demonstrate demonstrate that my name is.

C

A lot of that Hospital.

A

To get documented documented here so any thoughts, opinions on this.

E

We expand the names, expand, what they meet.

E

One of the operations gets well either the ad or the scope gets written out and fold at the multiply and the neg don't so it just makes them hard to read. For me, I would prefer a small ad instead of mad F mold silver, or something like that. Okay,.

F

E

Ad I don't think the saving those two to four characters in the opcode and.

B

A

May have been just like copied from the vector here's a little wicked do the sands were added with a review permanence I. Think, though it's just were inherited from the active open sourcing. So, okay, great um suggestion, I'm just looking quickly at the pull request that was open for these and the properties table for these off codes. It says that the opcodes have three children of unspecified type.

A

This correct or either.

C

One not to the scalar.

A

Ones they should be floated double clicked.

B

A

B

A

That would be something to I believe that was probably copied from the vector one. Okay,.

B

Yeah, it should be floater double.

A

Any other thoughts was there a clear.

D

New page or motivation for this origin, um so we thought what you said made it ago about simple fire finding patterns and threatens this so the what can happen after that, but that's good what could happen after the simplified? That's good! What can happen after these things are created. That can't happen if they were left alone, everest multiplication.

A

Well, I guess the the there's motivation for finding them in a common place right as opposed to having beach back and recognize the pattern and turn them into an actual like a single instruction. He actually does have. Maybe there's even another pole request. That's kind of a work in progress that may or may or may not see the light of day where the pattern actually is recognized in the back end and the comments that he received on that were actually is recognized earlier.

A

More commonplace, so doesn't necessarily have to happen roots of the fire, but could happen, but there are some benefits, perhaps to here from folding and the propagation, whatever effort for recognizing them earlier power.

E

Has instructions these operations yeah.

D

E

This is talking to twin sixty-six, but you know reason why can't be right.

A

We have, um if you look at the implementation, that we have on f mas. It's got a very mixed history. In the code base, there seems to be three distinct eras in which f mas are introduced, and there is some very early code that was introduced to try to recognize an extreme corner cases for Java I, think that was done on the.

B

A

Sure and I think power as well and then I think later on. There was another mapping of FMA instructions to or FMA op codes. I think this were the double to the vector ones came in under control of an option. I think that's only done on Z if it's float math option which doesn't do anything at the moment, but we still code guarded with it and then there's this attempt here. So you want to clean this up to have one sort of consistent way of doing it.

A

There's these op codes, but then there's another sort of thing that he's working on as well for java 9, where there actually is a map that FM a method that was introduced to the math class math class, where they were Java, allows you to use to do 24, kaatham, a arithmetic basically and he's snapping that method to instructions in the back ends of supporters, so that won't use this. These are like 400, Marvell, non Java language ism.

A

E

The first of the conditionally generate these as participant simplification, depending on some code, generator query, yep.

A

That and whether or not the language environment supports response, one is.

E

The cogent point in time statement: it's just that we're we haven't implemented the other codons or not all clintus, which is my support. This.

A

The kokkonen question would be whether or not there's actually support there for it, whether or not potentially you actually want this. We actually want to do this victory coming. You have an option at this and what I don't want to do this, and whether or not the target is that they'd be at the target processor that your donor encode for actually supports these East.

B

E

There is a missing.

F

E

Them sorry, those queries right now we're missing from the full request, interpreters and buoyant support. Yes,.

D

Really complication power where an MMA doesn't behave, the same multiplied at a fully remember the exact details. There is something wrong: it's.

A

D

Internal precision of it is a.

A

Shame you forget yeah and.

D

And getting a little bit whatever so that wrinkle would have to with.

A

The fact that it has slightly different kind of comes out in the.

D

Question that you'd asked the language front-end I'm.

A

Going to do but but it doesn't rip necessary or fun I guess you might need a further refinement of it. The question may not be is so simply do to support FM a might be. You support us a page with these kind of semantics.

A

The subtle piece of bats haven't thought through refine those questions. Pimples, you can.

B

Follow such as immune, it's the differences between, let's say a power.

A

Fm, a an X, a beast, a crab ma and if there's some subtleties there, that there are, there are ton of to another one it'll pass.

D

Mac and F min don't don't behave the same way as X plus the wire term. X else walk our babe, the I Triple E definition of min and Max difference with the wheel. They don't.

A

Generate Excel, okay, well, I mean those kinds of questions we need to probably surface in that arithmetic layer, which is pretty thin right now.

E

So in the pull request right now, it looks like there's nothing that would actually generate in any one of these instructions right it resistible fire handler for right these types of operations of some of the operands or constant, but something would happen. Actually you.

A

Have to generate the behaves bezel code anyway, see tests like trail tests or something like that. I would drive drive this.

B

Somebody smile today.

A

Okay, so I guess next steps and this one is to again similar to the ones that the previous one is deprived, provide more details on the semantics of these and sort of the testing strategy, for this also got that extra wrinkle about folding. These things that and the floating-point semantics that we haven't. Really, we don't have a solution yet.

A

Okay, anything else.

A

Okay, all right thanks. Everyone we'll have another architecture meeting in in two weeks and I'll get the agenda up there so that people can add proposed ideas. I already have one thing in mind: already somebody lined up for that which might take the entire time but feel free to add. When you see, if you think you want to add something to that thanks, everyone.

A