similar to: [LLVMdev] request for tutorial

(Sorry about the wall of text, it ended up as a brain dump of a bunch of backend-related documentation that I know about/have bookmarked in the past. Hopefully there's something useful in there.) If you haven't stumbled across them already, these might be helpful: http://llvm.org/devmtg/2009-10/Korobeynikov_BackendTutorial.pdf http://jonathan2251.github.io/lbd/

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.

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

Yes, I quite liked the things I've read about the PBQP allocator. Given what the hardware folks have to go through to get 1% improvements in scalar code, spending 20% (or whatever) compile time (under control of a flag) seems like nothing. And falling back on "average code" is a little disingenuous. People looking for performance don't care about average code; they care about

> The underlying liveness datastructure is a list of ranges where each vreg is alive > (ranges in terms of instructions numbered). I remember a couple of later linear scan > papers describing the same thing (Traub et.al. being the first if I remember correctly). > That should be as accurate as you can get in terms of liveness information. It depends on the details. For example, given

> On Sep 10, 2018, at 5:25 PM, Matthias Braun <mbraun at apple.com> wrote: > > > >> On Sep 10, 2018, at 5:11 PM, Preston Briggs <preston.briggs at gmail.com <mailto:preston.briggs at gmail.com>> wrote: >> >> The phi instruction is irrelevant; just the way I think about things. >> The question is if the allocator believes that t0 and t2

How precise is the interference checking (to my mind, a great weakness of linear scan)? Is there way to do coalescing (the great strength of coloring)? I ask these questions because we (guys I work with) see loops where there's a little register juggling that seems unnecessary. Is there a paper that describes what y'all do? Thanks, Preston On Mon, Sep 10, 2018 at 9:57 AM, Matthias

Thanks all, for all the pointers. I'd read some of them, but others are new. Jim, I'd certainly appreciate the chance to get together at the dev conference. I think y'all's ideas of a stub back end sound good, though I can appreciate the maintenance difficulties. Karen's idea for a new design guide is also good, though I think the idea of looking at other back ends for examples

I think y'all underestimate how important documentation can be. There are, after all, documents out there that purport to be guides to writing a back end for LLVM. I know of 2 other experienced & motivated compiler writers who read the available documentation, wrote some code, foundered, gave up, and wrote their own back end from scratch. So there's three of us that I know about, and I

On 25 September 2013 22:13, Preston Briggs <preston.briggs at gmail.com> wrote: > A lot of my difficulty in reading other examples is that it's not clear > what matters and what doesn't. It's what I hope to get by sitting next to > someone and asking questions. Some of this could be addressed in a guide. > I'd start with a chapter on planning. > Another

On 25 September 2013 12:28, Sean Silva <chisophugis at gmail.com> wrote: > > > > On Wed, Sep 25, 2013 at 7:02 AM, Renato Golin <renato.golin at linaro.org> > wrote: >> > (Devil's advocate, but half serious): > > It may be a good idea to require that the dummy backend is kept up to date, > as a way to keep a pulse on changes to the interfaces between

On Thu, Sep 26, 2013 at 12:22 PM, Preston Briggs <preston.briggs at gmail.com>wrote: > I think y'all underestimate how important documentation can be. > I'm a strong proponent for good documentation, and whenever I get a solid understanding of a specific part of LLVM I will usually write documentation for it. (I'm pretty clueless about backend stuff, which is why I

Erkan, you're right. Sorry about that. Attached is the most recent version. Preston Hi Preston, > I am trying to use DA as well. I used your example and commands that you > wrote in order to get DA information. > However, it does not report any dependence info. > I am wondering whether your local copy differs from the one on the > repository ? > Thanks. > Erkan.

On Wed, Oct 3, 2012 at 10:15 AM, Matthieu Moy <Matthieu.Moy at grenoble-inp.fr> wrote: > Preston Briggs <preston.briggs at gmail.com> writes: >> Think about costs asymptotically; that's what matters. Calls and >> returns require constant time, just like addition and multiplication. > > Constant time, but not necessarily constant memory. > > Deep recursion

Hi all, Unfortunately, all my Hunks are failed when I apply : patch -p1 < da.patch command. The problem might be due to the fact that da.patch file was created against revision 167549, but I am on revision 167719 (I believe the most recent one). I am not sure if this cause the problem ? But Preston may I ask you to generate the patch file against revison 167719 ? Thanks in advance. On

On 11/02/2012 11:02 AM, Hal Finkel wrote: > ----- Original Message ----- >> From: "Tobias Grosser" <tobias at grosser.es> >> To: "preston briggs" <preston.briggs at gmail.com> >> Cc: "Benjamin Kramer" <benny.kra at gmail.com>, "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu> >> Sent: Friday, November

On 11/02/2012 10:21 AM, Preston Briggs wrote: > > My initial guess is that a conservative fix is quick and small (make > sure the underlying pointers are loop invariant, otherwise give up). A > better approach would be to somehow turn code like the example into > array references that can be analyzed. I'll need to think about this and > do some reading. Hi Preston, I looked

Preston, thanks for the explanation and patch. Now it's printing the direction and distance values. On Tue, Nov 13, 2012 at 12:22 PM, Preston Briggs <preston.briggs at gmail.com>wrote: > Erkan, you're right. Sorry about that. > Attached is the most recent version. > > Preston > > > > Hi Preston, >> I am trying to use DA as well. I used your example

I'd like a value, call it Bottom, such that SE->getAddExpr(Bottom, X) => Bottom SE->getMulExpr(Bottom, X,) => Bottom isKnownPredicate(any, Bottom, X) => false etc. I can write code to make NULL work like I want, but it would be simpler if something was already defined. I'm wondering about SCEV::Unknown. The documentation suggests I could perhaps use it for a

My problem was that the constructor for DenseMap has an undocumented constraint. explicit DenseMap(unsigned NumInitBuckets = 0) { init(NumInitBuckets); } if given an explicit argument, requires that the argument be a power of 2. It's checked by an assert in init(), but for some reason my code didn't trip the assertion. Is there a special way I must make to enable asserts? Thanks,