similar to: [LLVMdev] Register allocation on IR

Having worked on SSA register allocators in the past I have to say that SSA is actually a good fit for register allocation. However LLVM IR is indeed not. You don't have any target instructions or register classed/constraints. It wouldn't make much sense to designate registers to llvm IR values nor is there a way to express that in IR. llvm has the machine instruction (MI) representation

Thanks. I will also work on doing an SSA register allocation that returns SSA form (IR), since it is not yet implemented. On Fri, Jun 12, 2015 at 9:20 PM, Matthias Braun <mbraun at apple.com> wrote: > llvm uses three different representations until machine code is emitted: > > - the llvm language as specified in the llvm manuals, we usually call that > IR > - the selection

Hi Andrew, > Somewhere during optimization PHI nodes on pointer types (including > alloca instructions) are being introduced, and they persist through the > scalar replacement of aggregates pass and others. I can't seem to find > a combination of passes or transformations to get rid of them. Has > anyone had this problem before, and know a transformation to eliminate > it?

On 08/20/2012 03:46 PM, Duncan Sands wrote: > Hi Andrew, > >> Somewhere during optimization PHI nodes on pointer types (including >> alloca instructions) are being introduced, and they persist through the >> scalar replacement of aggregates pass and others. I can't seem to find >> a combination of passes or transformations to get rid of them. Has >> anyone

Hi Ben, That did help. I continue to notice the virtual register in the program. I use LLVM 3.4. The program i am looking at is a very simple one. Listed below int global_var; int *global_ptr; int32_t main(int32_t argc, char ** argv){ int p = 10; int k = 20; int *pp; char *c_pp; pp = &k; global_ptr = pp; pp = &p; global_ptr = &global_var; return 0; } BR/Nizam

Hi Leslie, I suggest adding these 3 papers to your reading list. Register allocation for programs in SSA-form Sebastian Hack, Daniel Grund, and Gerhard Goos http://www.rw.cdl.uni-saarland.de/~grund/papers/cc06-ra_ssa.pdf Simple and Efficient Construction of Static Single Assignment Form Matthias Braun , Sebastian Buchwald , Sebastian Hack , Roland Leißa , Christoph Mallon , and Andreas

On Fri, 2007-08-10 at 00:51 -0500, Seung Jae Lee wrote: > Hi, guys. > > I'm interested in using reg2mem pass but not sure about the concept of it. > Can you let me know a reference about it, if any? > Forgive my ignorance. -_-; The reg2mem pass undoes SSA form. That is, it turns SSA registers into alloca instructions with loads and stores. > > Thanks, > Seung J.

Somewhere during optimization PHI nodes on pointer types (including alloca instructions) are being introduced, and they persist through the scalar replacement of aggregates pass and others. I can't seem to find a combination of passes or transformations to get rid of them. Has anyone had this problem before, and know a transformation to eliminate it? My optimization passes rely on

Hello all, I am trying to use the LLVM libraries to do register allocation on LLVM IR code -- and output IR as the result. There are two problems that arise when we try this : a. The LLVM backend requires that one goes through all the steps sequentially namely -- Instruction selection -- Scheduling and Formation -- SSA-based machine code optimizations -- Register

All register uses are SSA. Memory is not in SSA. The mem2reg pass which promotes stack variables to registers effectively converts non- SSA to SSA. There was a reg2mem pass, written by Andrew Lenharth, I'm not sure if it's still being maintained. On Jul 7, 2008, at 8:47 AM, Matthieu Moy wrote: > Hi, > > Silly question from an LLVM newbie: the LLVM LRM say that the

On 01/22/2011 10:30 PM, Surinder wrote: > Hi, > > I am emitting llvm bit code using > > llvm-gcc -c -emit-llvm -O0 -o test.bc test.c > > and then optimizing it with > > opt -O3 -print-module test.bc > > in order to obtain a dump of generated IR. > > > The resulting code has Phi nodes and is perhaps in SSA form. I want > to undo the SSA form while

I tried using the mem2reg pass with opt, e.g. opt -reg2mem x.bc > x2.bc where x.bc was produced with: llvm-gcc -O2 -emit-llvm -c x.c -o x.bc This did not reduce the # of variables in x2.bc I use -O2 because it produces the least # of instructions and hence the least # of new SSA virtual registers. Do you have a set of options to give to llvm-gcc or opt in mind ? My goal is to take a .c

On 6 July 2017 at 23:13, Chris Lattner <clattner at nondot.org> wrote: >> Yes, as an extension to VectorType they can be manipulated and passed >> around like normal vectors, load/stored directly, phis, put in llvm >> structs etc. Address computation generates expressions in terms vscale >> and it seems to work well. > > Right, that works out through

Hi, Diego, Thanks for your quick reply. Inserting a copy instruction may not work here because I have a limitation of virtual register number. I need to assign registers with ssa form to registers without ssa form. I will look the source code you point out. Thanks Xiangyang On Fri, Apr 24, 2015 at 4:19 PM, Diego Novillo <dnovillo at google.com> wrote: > > > On Fri, Apr 24, 2015

Hi Jakob, After reading your blog article, I have some questions. :-) In [1], it says: "It was an important design goal to make the algorithm as flexible as possible, and to avoid introducing arbitrary constraints. It is possible to change machine code and live ranges at any time. Simply evict the relevant live ranges, make the change, and put them back on the queue." Q1. The

LiveVariables is the optimized and tested way to get variable liveness information (it's used by register allocation). Unfortunately it requires a MachineFunction to work - so you'll either need to lower to one of the built-in targets or add your own target to acquire access to this pass. Andrew On 03/31/2011 12:28 PM, Carlo Alberto Ferraris wrote: > I've read that LiveValues

Hi, Sorry if this question has been asked earlier: Is the -reg2mem the pass to convert SSA form of LLVM IR to non-SSA form (ie, eliminate all phi-functions from LLVM IR) ? I tried it with a small example and it did remove all the phi function, I just wanted to confirm that the pass guarantees to remove all phi functions. Also, assuming I have this pass as a required pass, is it safe to clone

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?

Hello. I am having difficulties to bundle MachineInstr instructions, before register allocation (RA). More exactly, I registered a simple pass in addPreRegAlloc() that is trying to create bundles. I see that it is written at http://llvm.org/docs/CodeGenerator.html#machineinstr-bundles: <<Packing / bundling of MachineInstr’s should be done as part of the register

I've read that LiveValues has been removed from trunk. Did it bitrot or was simply removed because a replacement is available? If it's the former, what caused the bitrotting? If it's the latter, what's the replacement? (I've found LiveVariables but I'm not sure it can be used in a ModulePass). b.r. -- Carlo Alberto Ferraris <cafxx at strayorange.com <mailto:cafxx