similar to: [LLVMdev] [LLVMDev] Phi elimination: Who does what

Aye, between all current register allocators the 'AU.addRequiredID(PHIEliminationID);' will cause phi's to be eliminated to copies, but this misses the point of my question. What I am asking, is how does stack know that the value of the variable which the resulting value of the phi is currently allocated at. For instance take the instruction: Machine Basic Block (mbb) 12 reg16666 =

At the moment, phi elimination happens before register allocation, so there can be no phis between memory locations. Cameron On Oct 5, 2010, at 4:19 PM, Jeff Kunkel wrote: > When doing phi elimination, does one have to communicate with the > stack space at all? The problem I see is two distinctly different > registers may have two distinctly different stack spaces. When these >

The allocator you are building, is it the Hack's and Goos's polynomial time algorithm? On Tue, Oct 5, 2010 at 7:14 PM, Cameron Zwarich <zwarich at apple.com> wrote: > There is nothing that currently handles this properly, as far as I know. If you have a phi > > c = phi(a, b) > > where a, b and c are all assigned distinct stack slots, then copies must be inserted in

There is nothing that currently handles this properly, as far as I know. If you have a phi c = phi(a, b) where a, b and c are all assigned distinct stack slots, then copies must be inserted in the predecessor. If registers have already been allocated, then this memory copy might require a temporary register (unless you're on an architecture like x86 that lets you do memory-to-memory copies

For spilling, I plan to use the Hack-Braun generalization of the furthest-first heuristic for SSA: http://pp.info.uni-karlsruhe.de/uploads/publikationen/braun09cc.pdf For coloring, there are a few different approaches you can take, e.g. dominator tree scan, puzzle-solving, or a modified graph coloring / coalescing heuristic like IRC. The best quality for the least amount of implementation effort

I will try to make a standalone test case but the one that is failing uses a custom back end, so it's not really portable. So is the plan to have the strong PHI elimination behavior rolled into other passes? Andrew On 06/20/2012 06:54 PM, Cameron Zwarich wrote: > I'm the person who wrote it, and it's not really maintained, as we decided we wanted to go in a different direction

I'm the person who wrote it, and it's not really maintained, as we decided we wanted to go in a different direction long-term by having fewer passes making independent coalescing decisions rather than more. At the time I stopped working on it, it worked fine on x86 but caused problems with armv7 NEON code. If you file a PR with a test case, I am happy to take a quick look and try to fix

I've started using the strong PHI elimination pass, and it seems to work beautifully (producing much better placement of copy instructions) - though I'm seeing that it triggers an assert in debug+assert builds. The assertion is on line 1388 of RegisterCoalescer.C. Attached is the -debug output from the machine optimization part of the optimizer, for the simplest test case I could

Also note: there may be multiple MachineBasicBlock's for a single BasicBlock. - David M On Fri, Oct 15, 2010 at 4:59 AM, Jeff Kunkel <jdkunk3 at gmail.com> wrote: > I don't think you can. > > The BasicBlock is a member of MachineBasicBlock. It is not inherited, > so it cannot be cast. The number of the MachineBasicBlock is not the > same as any BasicBlock values.

Hi, In PHI node elimination pass to insert the copy in the predecessor block, there is a check if terminator is not an invoke instruction then place the copy there only. However for invoke terminator instruction a safe position is located for copy insertion. My doubt is why is this safe location search done only for invoke instruction and not for other terminators such as branch.

Sachin.Punyani at microchip.com wrote: > > Hi, > > > > In PHI node elimination pass to insert the copy in the predecessor > block, there is a check if terminator is not an invoke instruction > then place the copy there only. However for invoke terminator > instruction a safe position is located for copy insertion. > > > > My doubt is why is this safe

Hello, we can get BasicBlock from MachineBasicBlock through MachineBasicBlock::getBasicBlock() function, but how can I get MachineBasicBlock of a BasicBlock? Thank you!

On Jul 3, 2009, at 4:01 AM, Sanjiv Gupta wrote: > Sachin.Punyani at microchip.com wrote: >> >> Hi, >> >> >> >> In PHI node elimination pass to insert the copy in the predecessor >> block, there is a check if terminator is not an invoke instruction >> then place the copy there only. However for invoke terminator >> instruction a safe

On Tue, Oct 18, 2011 at 2:59 PM, Cameron Zwarich <zwarich at apple.com> wrote: > On Oct 18, 2011, at 2:53 AM, Chandler Carruth wrote: > > > Hello, > > > > I'm working on basic-block placement optimizations based on branch > probability information. I've run into a stumbling block though. One of the > existing passes to do this, essentially a dead pass

I don't think you can. The BasicBlock is a member of MachineBasicBlock. It is not inherited, so it cannot be cast. The number of the MachineBasicBlock is not the same as any BasicBlock values. So MachineFunction::getMachineBasicBlock( BasicBlock::{get the number} ) cannot work. I do not see much in the basic block which can identify it. So you can search for it. typedef struct findBlock {

On Oct 18, 2011, at 3:07 PM, Chandler Carruth wrote: > On Tue, Oct 18, 2011 at 2:59 PM, Cameron Zwarich <zwarich at apple.com> wrote: > I think this should really live as a CodeGen pass. Is there any good reason to make it an IR pass? > > So, as it happens, I was *completely* wrong here. CodeGen correctly preserves the ordering of blocks from IR, *unless* it can do folding,

Hi, The PHI elimination pass calls the function copyRegToReg for copy placement and then later tries to setkill to the temporary virtual register used in copy placement. For this setkill action it looks only in one instruction (last instruction for copyRegToReg) for virtual register with no use. My target has only one register and I can't do copyRegToReg in one instruction only. So I

Good Afternoon. I am a Computer Science undergraduate student in Brazil and as completion of course work, I am developing an register allocator, using the infrastructure of the LLVM. To accomplish this task, I have based my implementation in allocators already implemented in LLVM. But a question came to me while I was researching in books and articles of compiler theory and own documentation of

Is there an easy way to obtain all liveout variables of a basic block? Liveins can be found for each MachineBasicBlock, but I can only find liveouts for the whole function, at MachineRegisterInfo. Do I need to find them out manually?

Hi all, I am really stumped on a problem for long. I could not figure out why. That is why i am here. OK, here is the problem: I tried to insert a MachineBasicBlock into a function. Here is the code snippet: // insert a machine basic block with the error_label into MF and before I // Pred is the predecessor of the block to be inserted // the new basic block is inserted right before I void