But, the branch folding pass, or whatever passes are supposed to reorder the blocks based on the CFG, are not doing so in this case. Otherwise there is no way that blocks 2 and 4 should be printing out before blocks 3 & 5. Renumber blocks just seems to reorder the values based on their pre-set block number, but when the CFG is modified these number should modified also to follow the new ordering, which is not occurring. ________________________________ From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Dale Johannesen Sent: Monday, October 13, 2008 5:28 PM To: LLVM Developers Mailing List Subject: Re: [LLVMdev] CFG modifcations and code gen On Oct 13, 2008, at 5:14 PMPDT, Villmow, Micah wrote: As stated in an earlier email, I am working on getting break/continue to work correctly for my backend, but I ran into another issue with codegen and the CFG. It seems that code gen is not done based on the CFG, but rather on the block numbers, and the function call MachineFunction::RenumberBlocks doesn't renumber the blocks based on the CFG. So how can I modify the CFG so that when codegen occurs, it follows the graph and not just does a linear scan over the MachineBasicBlock vector? It's not intended to work that way. The BranchFolding pass, which runs later, is responsible for rearranging things into a more reasonable order. In the attached dot file, block 2 gets printed before block 3 and 5 and block 4 gets printed between blocks 3 and 5. This obviously is not what the CFG is saying it should be done. The code I'm using to do this transformation, which takes 2 & 4 and places them after block 5 is: MachineBasicBlock* newExitPath = findLowestNumSuccBB(root); pHigh->addSuccessor(newExitPath); root->removeSuccessor(newExitPath); root->CorrectExtraCFGEdges(*root->succ_begin(), NULL, false); pHigh->CorrectExtraCFGEdges(*pHigh->succ_begin(), newExitPath, false); newExitPath->moveAfter(pHigh); root->getParent()->RenumberBlocks(); So what am I doing wrong? Thanks, Micah Villmow Systems Engineer Advanced Technology & Performance Advanced Micro Devices Inc. 4555 Great America Pkwy, Santa Clara, CA. 95054 P: 408-572-6219 F: 408-572-6596 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20081014/62772382/attachment.html>
On Oct 14, 2008, at 9:16 AM, Villmow, Micah wrote:> But, the branch folding pass, or whatever passes are supposed to > reorder the blocks based on the CFG, are not doing so in this case. > Otherwise there is no way that blocks 2 and 4 should be printing out > before blocks 3 & 5. Renumber blocks just seems to reorder the > values based on their pre-set block number, but when the CFG is > modified these number should modified also to follow the new > ordering, which is not occurring.Did you implement TargetInstrInfo::AnalyzeBranch for your target? Check out the large comment above it in TargetInstrInfo.h -Chris -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20081014/79a665e2/attachment.html>
Chris, I took a look at AnalyzeBranch and I don't see how it can solve my problem. The issue itself isn't with branching, as I can handle branches fairly well in my custom pass(see the before and after dot files attached). I can take a bunch of branches and construct high level control flow for my backend since I have no ability to do goto/jump, only whileloop and ifs. So analyzing the branch's isn't the problem. The problem comes with emit'ing the code. Even though I've renumbered the blocks and re-ordered the CFG into a more sane control flow. The code emitter still processes the blocks in the old order. So instead of going from 0-5, it prints out the instructions in the order, 0, 1, 2, 5, 3, 4. This is the order that the old CFG is in, not the new one after this pass is done. I've added this analysis pass as a PreEmitPass, is this the correct location to implement this? Or should I be implementing it earlier? Later? Thanks for any advice, ________________________________ From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Chris Lattner Sent: Tuesday, October 14, 2008 9:50 AM To: LLVM Developers Mailing List Subject: Re: [LLVMdev] CFG modifcations and code gen On Oct 14, 2008, at 9:16 AM, Villmow, Micah wrote: But, the branch folding pass, or whatever passes are supposed to reorder the blocks based on the CFG, are not doing so in this case. Otherwise there is no way that blocks 2 and 4 should be printing out before blocks 3 & 5. Renumber blocks just seems to reorder the values based on their pre-set block number, but when the CFG is modified these number should modified also to follow the new ordering, which is not occurring. Did you implement TargetInstrInfo::AnalyzeBranch for your target? Check out the large comment above it in TargetInstrInfo.h -Chris -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20081014/8b38eb37/attachment.html> -------------- next part -------------- A non-text attachment was scrubbed... Name: before_control_flow_pass.dot Type: application/octet-stream Size: 2896 bytes Desc: before_control_flow_pass.dot URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20081014/8b38eb37/attachment.obj> -------------- next part -------------- A non-text attachment was scrubbed... Name: after_control_flow_pass.dot Type: application/octet-stream Size: 2455 bytes Desc: after_control_flow_pass.dot URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20081014/8b38eb37/attachment-0001.obj>