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Hi. Im currently investigating LLVM's implementation of PBQP as a part of a bachelors thesis im doing on register allocation for regular architectures. In particullar, im looking at the possibility for improving the spill rate of PBQP for a particular DSP architecture, by using register pairing. >From reading the source code of lib/CodeGen/RegAllocPBQP.cpp i conclude that support for

...target and set PBQP to be the default allocator for your system. If the CodeGen framework can represent this kind of pairing constraint now you could add your new PBQPBuilder to CodeGen so that other target writers can benefit from it. See lib/CodeGen/RegAllocPBQP.cpp for examples of how to write PBQPBuilders, and I'm happy to answer any questions, time permitting. :) Cheers, Lang. On Wed, Apr 27, 2011 at 5:59 PM, Jakob Stengård <jakobste at kth.se> wrote: > >Can you describe your pairing constraint in more detail? I've seen a few > different kinds of "pairing", and...

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 Arnaud, I'm glad to hear that your test case is working. I however still get my wrong allocation in some non trivial cases : the > pairing constraint is not fulfilled. > > I have tried to modify the 'ensure pairable' pass (the pass undoing some > of the coalescer's work) to always insert register copies for > instructions with the pairable constraint, instead of

Hi Lang, The assert is not triggered any longer on my testcases :) I however still get my wrong allocation in some non trivial cases : the pairing constraint is not fulfilled. I have tried to modify the 'ensure pairable' pass (the pass undoing some of the coalescer's work) to always insert register copies for instructions with the pairable constraint, instead of being smart and

Hi Lang, Thanks a lot for taking time to look into this. I will test the fix soon and let you know the results. Cheers, -- Arnaud de Grandmaison On Tuesday, April 03, 2012 17:30:33 Lang Hames wrote: > Hi Arnaud, > > Apologies for the delayed reply. > > Thank you for the excellent test case - it exposed a subtle bug in the > colorability heuristic. This has been fixed in

On Jun 6, 2011, at 7:07 AM, Arnaud Allard de Grandmaison wrote: > 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

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 Lang, I have reduced the testcase as much as possible. The log of the run and the dumped graphes are attached. Cheers, -- Arnaud de Grandmaison On Tuesday, March 27, 2012 01:20:35 Lang Hames wrote: > 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

Hi Arnaud, Apologies for the delayed reply. Thank you for the excellent test case - it exposed a subtle bug in the colorability heuristic. This has been fixed in r153958. In case you are curious, the bug was as follows: the PBQP solver applies applies a simplification step to each matrix. When all elements of a matrix row or column are equal, the value for those elements is "pushed

Hi All, 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. First a quick bit of background: The PBQP allocator is based on ideas described in [1]. I implemented this algorithm (with the improved heuristic

Hi Arnaud, LiveInterval::markNotSpillable() sets the live interval's spill weight to infinity. For well-formed PBQP graphs (i.e. ones that have some finite-cost solution), PBQP should never chose to spill such an interval. The two possibilities for this crash are that the input graph has no finite-cost solution, or that you've exposed a bug in the PBQP solver. >From memory your target

Arnaud, another way to look at it, if the description of your register sets includes "pairs", is that your assembly language syntax for MPQD is redundant, operand-2 is the second half of the register-pair in operand-0, so an alternative is to let llvm think this is a two operand instruction (one of them being a pair) rather than a three operand instruction. even

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