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...or even faster than the current allocators (so please don't say "you'd better use a better algorithm" :-)). I've been reading the code of current allocators as well some documentation about them in blogs, etc., but I still have some doubts. I need to create a graph with the interference between LiveIntervals, where each node is a LiveInterval and an edge between two of them means they interfere. By "X interferes Y" I mean: "LiveInterval X and Y must me mapped to some register of a class Z AND there's an interception between the ranges of X and ranges of Y"...

...the current allocators (so please don't say "you'd better use a better algorithm" :-)). > > I've been reading the code of current allocators as well some documentation about them in blogs, etc., but I still have some doubts. > > I need to create a graph with the interference between LiveIntervals, where each node is a LiveInterval and an edge between two of them means they interfere. > > By "X interferes Y" I mean: "LiveInterval X and Y must me mapped to some register of a class Z AND there's an interception between the ranges of X and ranges...

Good Night. I'm implementing a Interference Graph in the Register Allocation pass. I'm building this graph BEFORE any assignment of a virtual register to physical register. But I have a doubt about how to check the interference between two Live Intervals (i.e. They live at same point), should I use: L1->overlaps(L2) Where L1 and L2...

Ok, just to clarify, RegUnits, as far I understand, are Physical registers or alias to Physical registers. They exist because some instructions use physical registers directly rather than virtual register. It's right? And why this RegUnits should be present in the Interference Graph? I thought were only the Live Intervals would be the nodes of the graph. Sorry about the trouble to understand my question, my English doesn't help that much, I'm from Brazil. Em 18/11/2015 10:19 PM, "Matthias Braun" <mbraun at apple.com> escreveu: > I'm not s...

Hi, Using Chaitin's approach, removing a copy via coalescing could expose more opportunities for coalescing. So he would iteratively rebuild the interference graph and check for more opportunities. Chaitin was also careful to make sure that the source and destination of a copy didn't interfere unnecessarily (because of the copy alone); that is, his approach to interference was very precise. The idea of computing interference from intersecting range...

...> >> The phi instruction is irrelevant; just the way I think about things. >> The question is if the allocator believes that t0 and t2 interfere. >> >> Perhaps the coalescing example was too simple. >> In the general case, we can't coalesce without a notion of interference. There is also logic in `LiveRange::overlaps()` that considers live ranges as not overlapping in some cases where they are related via copy instructions. This will also effect the interference during the main allocation algorithm. >> My worry is that looking at interference by ranges of inst...

...e mar. 11 sept. 2018 à 10:23, Preston Briggs > <preston.briggs at gmail.com> a écrit : > > > > Hi, > > > > Using Chaitin's approach, removing a copy via coalescing could expose > more opportunities for coalescing. > > So he would iteratively rebuild the interference graph and check for > more opportunities. > > I am not sure Chaitin's approach would lead to a better coalescing > than what LLVM does. > I believe most of the copies that we see in the final code comes from > live-range splitting (i.e., to avoid spill), not coalescing, but I...

...efined and used in block C, after which it is dead. A traditional live variable analysis would say that x and y do not interfere. However, what happens if the linear ordering of instructions puts block C before block B? Then it seems to me that the live intervals overlap and we'd see a false interference. Does the ability of LiveIntervals to have holes in them take care of this problem? Let's say block A has instructions 1-10, block C 11-20 and block B 21-30 and that x is defined at instruction 1 and last used at instruction 30. Let's say y is defined at instructions 11 and last used at...

The phi instruction is irrelevant; just the way I think about things. The question is if the allocator believes that t0 and t2 interfere. Perhaps the coalescing example was too simple. In the general case, we can't coalesce without a notion of interference. My worry is that looking at interference by ranges of instruction numbers leads to inaccuracies when a range is introduced by a copy. But perhaps I should focus on the links and, as you suggested, the debugging info. Thanks, Preston On Mon, Sep 10, 2018 at 5:02 PM, Matthias Braun <mbraun...

...than linear scan IMO (though doesn't really matcher >> either approach). >> >> RegAllocGreedy assigns the registers in an order based on the priority >> value computed in enqueu() we are not just scanning from top to bottom of >> the program. We also perform actual interference checks we just don't >> happen to build up an explicit interference graph up front. >> >> - Matthias >> >> On Sep 10, 2018, at 9:49 AM, Preston Briggs via llvm-dev < >> llvm-dev at lists.llvm.org> wrote: >> >> Why have we ended up using line...

...s not supported on it. However we suppose that could be possible put the two disk images in different HDD''s and use the iostat tool from the sysstat suite (which allow to sees disk activity in a per-device basis) to observe the behavior. - Is the behavior ok? We mean, we consider that this interference is undesirable for certain deployments (anyone with paravirtualized and HVM guests in the same box, like in example Linux+Windows2003, and you want a fair share of the disk transfer rate). What we are asking is if this is a consequence of the Xen design and a known behavior, and if there is a worka...

...that doesn't work with the register allocator of choice, we can output an error (or a warning and override the choice). > >> Also, on this particular file below. Seems to me these queries do not >> belong to the register allocator. Perhaps a utility class that tracks >> interference information that can be accessed by both the allocator >> and the coalescer? Also, why is coalesceThisCopy() needed? Shouldn't >> the coalescer be responsible for making the decision? > > Register allocators know information about interference, for example, > the interferen...

Hi, I worked in llvm to get some information from live variable analysis. If the live range of one variable interferes with another, we could record the related two variables into a pair. For example, with a function with local variables 'a', 'b', 'c', 'x' and 'y', the pair set { (a, b), (b,c), (x,y)} indicates that 'a' interferes with 'b',

Hi, I have a frontend that could insert many calls to an external threading library, my problem is that would interfere with optimizations, particularly the inliner. Is there some way to do this ? I've considered leaving textual markers in function names, is that a legitimate solution ? James -------------- next part -------------- An HTML attachment was scrubbed... URL:

...intended to be used as an internal interface, but if you really > would like it, I would have no problem promoting it to be a public > interface. Let me know what you'd like. A public interface. the interface of LiveIntervals is more convenient than LiveVariables when building build the interference graph, which is necessary for the family of Chaitin style register allocators. Actually I am surprised that some common graph like the interference graph and the data dependence graph (a.k.a. data precedence graph or scheduling graph) is not available in CodeGen, except the control flow graph. Tho...

...passes could make use of it. > For now, I think we leave it as it is. If the user picked a > coalescer that doesn't work with the register allocator of choice, we > can output an error (or a warning and override the choice). Ok. > > Register allocators know information about interference, for example, > > the interference graph in a coloring allocator. The classic > > coalescing > > algorithm examines the interference graph and looks for copies between > > allocation units whose corresponding nodes do not have an edge between > > them in the graph. T...

...C, after which it is dead. > > A traditional live variable analysis would say that x and y do not > interfere. However, what happens if the linear ordering of > instructions puts block C before block B? Then it seems to me > that the live intervals overlap and we'd see a false interference. > > Does the ability of LiveIntervals to have holes in them take care > of this problem? Let's say block A has instructions 1-10, block > C 11-20 and block B 21-30 and that x is defined at instruction 1 > and last used at instruction 30. Let's say y is defined at > inst...

Hi Kameshwar, You're best off sending emails such as this to the LLVM developers mailing list (llvmdev at cs.uiuc.edu). You'll reach a much wider audience. The PBQPRegAlloc::buildInterferenceMatrix method constructs a PBQP cost matrix representing a single interference constraint, which doesn't sound like what you want. It is only used by the PBQP allocator (-regalloc=pbqp), whereas LLVM uses linear scan by default (-regalloc=linscan). That's why you're not seeing it called....

...dead. >> >> A traditional live variable analysis would say that x and y do not >> interfere. However, what happens if the linear ordering of >> instructions puts block C before block B? Then it seems to me >> that the live intervals overlap and we'd see a false interference. >> >> Does the ability of LiveIntervals to have holes in them take care >> of this problem? Let's say block A has instructions 1-10, block >> C 11-20 and block B 21-30 and that x is defined at instruction 1 >> and last used at instruction 30. Let's say y is...

...an internal interface, but if you really >> would like it, I would have no problem promoting it to be a public >> interface. Let me know what you'd like. > > A public interface. the interface of LiveIntervals is more convenient > than LiveVariables when building build the interference graph, which > is necessary for the family of Chaitin style register allocators. Ok. > Actually I am surprised that some common graph like the interference > graph and the data dependence graph (a.k.a. data precedence graph or > scheduling graph) is not available in CodeGen, except th...