similar to: PBQP register allocation and copy propagation

Hi James, I’ve tried to play in the past with the allocation order, which can definitely be tweaked and improved. The metric we use for spill cost being what it is (i.e. not targeted for PBQP, but that’s a different subject), I found it made real sense to use some other heuristics to sort nodes (on top of the spill cost) when there was a tie between them. Of course, that’s a heuristic and it can

Hi, > > I think one idea to improve the situation is to consider the cost vector of adjacent nodes during RN. Let's say you decided to do a RN for node A and want to compute the costs for choosing register %Ri. The current implementation does this by computing min(row/column i of edge A <--> B) but you can do better by adding B's cost vector to the row/column before computing

> (1) Spill cost metrics. I think this one cannot be dissociated from some kind of live range pre-splitting. Cheers, Arnaud From: Lang Hames [mailto:lhames at gmail.com] Sent: 03 June 2016 23:15 To: James Molloy Cc: Arnaud De Grandmaison; llvm-dev at lists.llvm.org; Sebastian Buchwald; Bernhard Scholz Subject: Re: [llvm-dev] PBQP register allocation and copy propagation Hi James, Arnaud,

Hi All, I finally had a chance to get back to my pbqp trials, now using the 3.0 release. I still hit the same assert : "Attempting to spill already spilled value." This is triggered because in RegAllocPBQP::mapPBQPToRegAlloc, a vreg node is either : - a physical register (problem.isPRegOption(vreg, alloc)), - or a spill (problem.isSpillOption(vreg, alloc)) The problem is that pass

Hi Lang, > From memory your target is not public, so I won't be able to reproduce > the crash myself. Is that correct? Correct. > If that's the case, I could add functionality to dump the PBQP graphs > during allocation. I think they should give me enough information to > debug the issue. Would you be able to share the PBQP graphs? I can share the pbqp graph if you send

Hi Arnaud, Thanks for attaching those files. I'll take a look at them. Commit r153483 adds an option to the PBQP allocator, "-pbqp-dump-graphs", to dump the PBQP graph for each round of each function in a compilation unit. The generated files are named "<module id>.<function>.<round>.pbqpgraph", and contain a simple text representation of the PBQP graph.

Hi Jakob, > Out of curiosity, how are you dealing with live range splitting and > coalescing in PBQP? I know you added the LoopSplitter pass. > > For linear scan in LLVM we are going in the direction of aggressive > coalescing before allocation, and on-demand splitting during allocation. > > I know that other allocators use no early coalescing, and coalesce during >

On Sep 20, 2010, at 7:53 AM, Lang Hames wrote: > I've just committed some changes to the PBQP allocator which are designed to make it easier to implement custom register allocation constraints. This is a quick summary of those changes, and of the status of the PBQP allocator in general. Thanks, Lang! Out of curiosity, how are you dealing with live range splitting and coalescing in PBQP?

Hi, Please see the two ".ll' files attached. Command line used llc -march=pic16 -pre-RA-sched=list-burr -regalloc=pbqp new.obc The above test case crashes only when I use the combination of list-burr scheduler and pbqp register allocator. If any of them (scheduler or register allocator) is replaced with some alternate then I don't see the crash. I could not figure

Hi, I would like to ask about PBQPs use of InlineSpiller. The code output when using PBQP gets a lot bigger compared to when using RegAllocGreedy. PBQP does not split the live intervals, and a lot more (often redundant) reload instructions are emitted as a result, it seems. I wonder why this is, and if there are any plans to improve on this point? /Jonas Paulsson -------------- next part

This is a known issue with the current PBQP data structures. I'm working on an overhaul of the PBQP allocator at the moment which should address this. - Lang. On Sat, Oct 20, 2012 at 2:08 PM, Benjamin Kramer <benny.kra at gmail.com>wrote: > > On 20.10.2012, at 22:47, Jordan Rose <jordan_rose at apple.com> wrote: > > > Hi, everyone. Today I was trying to build LLVM

Hi all, I was wondering about whether the PBQP register allocator is likely to be maintained in the future. It's proving to be a nice way to encode some instruction encoding constraints for an out-of-tree backend we have, but there's concern about it being abandoned or bitrotting in the future. Also, if PBQP is likely to lapse out of regular maintenance in the future, is there a simple

This looks like a bug in the PBQP solver. I'm currently investigating. Cheers, Lang. On Thu, Nov 12, 2009 at 12:46 AM, <Sachin.Punyani at microchip.com> wrote: > Hi, > > > > Please see the two “.ll’ files attached. > > > > Command line used > > llc –march=pic16  –pre-RA-sched=list-burr –regalloc=pbqp new.obc > > > > The above test case

Hi All, My target has some instructions requiring register pairs. I decided to give a try to the PBQP allocator : it is working fine in 99% of the cases, but I am stumbling on the following issue. Instruction 'MPQD' takes 3 register operands inputs, with the constraint that operands 0 and 2 must be consecutive registers. Operand 1 has no particular constraint. It has no output register.

Hi Sachin, Confirmed: This is being caused by a subtle issue in the heuristic PBQP solver. Specifically: R1/R2 reductions as currently implemented can, on rare occasions, lead to the heuristic solver failing to find a finite cost solution, even though one exists. The infinite cost solution will always be in violation of some rule of register allocation (failing to handle an interference, or

Hi, everyone. Today I was trying to build LLVM with libc++ and C++11 enabled, and I ran into this: http://stackoverflow.com/questions/10065384/instantiation-of-a-list-with-an-incomplete-type-in-a-typedef Basically, PBQP/Graph.h forward-declares classes, then tries to get iterators for std::lists of those classes. This is technically undefined behavior. I tried fudging with the order of

Hello Sir, Im trying to test run pbqp register allocator for small C programs. by llc -regalloc=pbqp -debug <bitcode of the file> It is giving me segmentation fault for even very simple programs having loops or if statements. Please tell me where I'm going wrong. -- Regards, Smriti Jaiswal MTech Dept of Computer Science and Engg, IIT Kanpur -------------- next part --------------

Hello, we are currently working on my project that aims at improving the register allocation scheme by identifying if the interference graphs are chordal or not. we are working on the llvm compiler .we are forcing the compiler to use PBQP register allocation scheme by an option of ' ' regalloc=pbqp ' during the execution of prgm. we have been succesfull in accessing the interference

Hi, I have worked a little on the PBQP register allocator, and it is quite clear (at least to me) that it is not even a serious alternative to RegAllocGreedy at the moment, due to the poor handling of spilling. As Arnaud wrote below, it is not optimizing spilling at all, but rather just spills anything that does not get an assignment. The result is a lot more spill/reload instructions than

Thanks Lang! I think we can use linear scan as work around for short term. Thanks for your help. Regards Sachin > -----Original Message----- > From: Lang Hames [mailto:lhames at gmail.com] > Sent: Sunday, November 15, 2009 10:08 AM > To: Sachin Punyani - I00202 > Cc: llvmdev at cs.uiuc.edu > Subject: Re: [LLVMdev] Crash in PBQP register allocator > > Hi Sachin, >