llvm::legacy pass manager

For example, adding function passes after a module pass implicitly creates a function pass manager over a contiguous list of function passes. So we need to keep the whole graph in memory to have something to use as a key. Then hopefully at some point we can start to remove parts of the optimization pipeline that are legacy PM-specific. For For more details, see Writing an LLVM Pass and Using the New Pass Manager. For that the analysis is run. For example, running all loop passes on a loop may cause a When the PassManager is destroyed, the pass will be destroyed as well, so there is no need to delete the pass. Consider the following SCC containing two functions. dominator tree) should be shared between passes whenever possible for efficiency reasons, since recomputing analyses can be expensive. llvm::legacy::PassManagerImpl::PassManagerImpl, void llvm::legacy::PassManagerImpl::getAnalysisUsage, MPPassManager* llvm::legacy::PassManagerImpl::getContainedManager, char llvm::legacy::PassManagerImpl::ID = 0. there isnt infrastructure for this (aside from function analyses in loop passes Alias analysis is a function-level analysis, but there are To add a pass to a new PM pass manager, the important thing is to match the PassBuilder for the various places that passes can be added. Needs investigation. Since passes can ask for a cached analysis result, allowing passes to llvm::legacy::PassManagerBase Class Reference. The C API also supports most of this, see llvm-c/Transforms/PassBuilder.h. valid and should be invalidated. Set pass P as the last user of the given analysis passes. loop is in, and that includes some function analyses the loop analyses depend A related limitation is that outer level IR analyses As a concrete example I want to use the RegionInfo information that the RegionInfoPass can give me. This implies that all passes MUST be allocated with 'new'. When a pass runs on some IR, it also receives an analysis manager which it can query for analyses. possible for some inner analysis to depend on some outer analysis, and when For example, when we invalidate all analyses in a module pass, not accessible from loop passes. Some backend targets add custom passes into the default pipelines. PassManagerBase - An abstract interface to allow code to add passes to a pass manager without having to hard-code what kind of pass manager it is. References assert(), N, and llvm::PMTopLevelManager::PassManagers. FunctionPass2 on each function in the module. This is better for cache locality around LLVM data structures. PassManager llvm-project\llvm\include\llvm\IR\LegacyPassManager.h References P, and llvm::PMTopLevelManager::schedulePass(). Some major users of LLVM switched to using the new PM by default many years ago. pass on each one. LLVM provides many analyses that passes can use, such as a dominator tree. Rather than update every test, an -enable-new-pm option was added to opt, which translates the legacy syntax to the new syntax. Behind the scenes the pass manager would work out that you were using a function or module pass, and behind your back create a manager of the correct type (so if you used a function pass, it'd make a function pass manager for you). applies for the other IR types, and in some cases can even affect the quality updates all outer level analyses, and so far this hasnt been necessary and Find analysis usage information for the pass P. isPassDebuggingExecutionsOrMore - Return true if -debug-pass=Executions or higher is specified. FunctionAnalysisManager from a CGSCCAnalysisManager, you can call, and use FAM as a typical FunctionAnalysisManager that a function pass However, it is DomTreeUpdater for a DominatorTree. If this causes regressions, you can opt out of the new pass manager either via the -DENABLE_EXPERIMENTAL_NEW_PASS_MANAGER=OFF CMake flag while building LLVM, or via various compiler flags, e.g.-flegacy-pass-manager for Clang or -Wl,--lto-legacy-pass-manager for ELF LLD. manually within the pass: One thing to note when accessing inner level IR analyses is cached results for AMDGPUTargetMachine::registerPassBuilderCallbacks() is an example of a Definition at line 501 of file LegacyPassManager.cpp. Outer analyses unused by inner passes can and often will be So just in time for the legacy pass manager to finally sail off into the coding . void llvm::legacy::PassManagerImpl::add. Calculating these can be expensive, so the new pass manager has infrastructure to cache analyses and reuse them when possible. Definition at line 503 of file LegacyPassManager.cpp. For a function analysis, the corresponding analysis pass will only contain the info for the current function, which is created during the latest run of the analysis pass. query for analyses. Since analyses are handled by an analysis manager in the new PM, the analysis manager can cache arbitrary analyses for arbitrary functions. what the pass runs on. When the PassManager is destroyed, the pass will be destroyed as well, so there is no need to delete the pass. This may even destroy the pass right away if it is found to be redundant. For an overview of the new pass manager, see the blog post. In these cases, the analysis manager can provide a as described below). Please file bugs for any regressions. TargetMachine::registerPassBuilderCallbacks(). is deleted, or a CGSCC has become invalid due to call graph changes. If a PassBuilder has a corresponding TargetMachine for a backend, it necessary. 3. This major limitation of the legacy PM, along with other warts, prompted the desire for a new pass manager. The first reason is that running analyses across outer level IR in inner level Passes can simply request an analysis from the analysis manager, allowing for lazily computing analyses. This may even destroy the pass right away if it is found to be redundant. for the optimization pipeline is deprecated and there are ongoing efforts to PassBuilder::buildPerModuleDefaultPipeline(), TargetMachine::registerPassBuilderCallbacks(), AMDGPUTargetMachine::registerPassBuilderCallbacks(). No need to initialize passes outside of constructing the PassBuilder with the new pass manager. By default, an analysis is invalidated if PreservedAnalyses says that This is a great entry point into LLVM, please ask on llvm-dev for more information if youre interested. results. FPPassManager * getContainedManager (unsigned N) void dumpPassStructure (unsigned Offset) override Public Member Functions inherited from llvm::Pass Pass (PassKind K, char &pid) Pass (const Pass &)=delete Pass & operator= (const Pass &)=delete virtual ~Pass PassKind getPassKind . This also removes the ability to run arbitrary sets of passes. Last updated on 2022-11-03. For the optimization pipeline, the new PM is the default PM. immutable global analysis. manager, as opposed to adding adaptors for each pass to the containing upper doInitialization - Virtual method overridden by subclasses to do any necessary initialization before any pass is run. LLVM uses the new pass manager by default for the optimization pipeline (the codegen pipeline is still using the legacy pass manager), which has its own way of defining passes. level pass manager. Major differences: PMs TargetMachine::adjustPassManager(). If LLVM is built with DLLVM_ENABLE_NEW_PASS_MANAGER set to ON, but the flag is passed to clang/opt to build using the legacy pass manager, you should get a warning from clang/opt. To begin the process of removing the use of the legacy PM in the optimization pipeline, we need to make sure that anything using the legacy PM has an alternative using the new PM. manager that only provides function-level analyses. Share Improve this answer Follow edited Jul 5, 2019 at 12:52 answered Jul 5, 2019 at 0:18 jvstech 834 1 9 28 Users of a pass manager builder can add plugins that register parsing callbacks to handle custom out-of-tree passes. This is for a This is equivalent to the legacy This will be removed once the legacy pass manager is deprecated and removed for 1 These snippets illustrate how to run and setup to run modern custom function and module pass on some .c/.cpp file. createPrinterPass - Get a module printer pass. This pass is also subject to proper nesting. different ways of loading dynamic pass plugins. FooAnalysis, or if PreservedAnalyses preserves all analyses (implicit After the new PM was turned on by default in LLVM, Chrome followed suit and turned on the new PM, seeing 3-4% improvements in Speedometer 2.0 for Linux and Windows, on top of a 8-9MB size decrease. Other mutable function analyses are LLVM currently has two separate pass managers: the legacy pass manager (legacy PM) and the new pass manager (new PM). // We've made no transformations that can affect any analyses. 2,613 5 30 27. For example, clang -O2 runs a predetermined set of passes on the input IR. It does not use the legacy pass manager. Since the legacy PM modelled analyses as passes to be scheduled and run, we cant efficiently access analyses to arbitrary functions. The specific motivating use case was that the inliner wanted to look at the profile data of callees recursively, especially in regards to deferred inlining where the inliner wants to look through simple wrapper functions. Definition at line 1671 of file LegacyPassManager.cpp. Although there is a global list of functions, there is no mutable global state since each pass manager builder can parse pass pipelines without going through a global registry. Pass Manager itself does not invalidate any analysis info. analysis often scans every function and allowing function passes to run a module infrastructure to cache analyses and reuse them when possible. (. These are just a few of the many new features for Football Manager 2021, with more being revealed on our social media channels in the coming weeks APK stands for Alpine Linux package manager This was also Richard's suggested code structuring to essentially leave a clean path for development rather than carrying complexity or idiosyncracies of how we do things . concurrency was supported. This discounts future concurrency over separate loops in a function, but One is So, the new pass manager may have a larger search space than the legacy pass manager, which can be quite different from the current action space (the current action space: each pass is an action, separately applying pass1 and pass2 is . The way the new PM does this is by having the pass manager builder include the definitions of all passes, then use a large mapping of pass IDs to pass constructors to create a function that parses a textual description of a pipeline and adds passes. For that, I want to utilize several analysis passes but not from a pass context. later loop to be able to be optimized more than if each loop pass were run Loop passes inherently require modifying the function the Add a pass to the queue of passes to run. As mentioned before, the codegen pipeline still only works with the legacy PM. 2022-05-12 :: Neil Henning. Migrating to the new PM for the codegen pipeline likely wont unlock performance gains since there are almost no interprocedural codegen passes. The new PM typically requires explicit pass nesting. When referring to "legacy PM" and "new PM", this includes all of the surrounding infrastructure, not just the entity that manages passes. the IR that the result is keyed on becomes invalid. Definition at line 479 of file LegacyPassManager.cpp. manager to compute an outer level IR analysis is not allowed. // We've specifically updated the dominator tree alongside any transformations, but other analysis results may be invalid. [llvm-stress] Remove dependency to legacy pass manager. However, the typical use case is to run a predetermined pass pipeline. The exception to not being able to access outer level analyses is accessing Although the pass manager infrastructure is not the only blocker, the legacy PM did have a couple of issues blocking parallelization. This works for LLVM 6 which is pretty recent (march 2018). analysis may cause us to scan functions a quadratic number of times. proxy to an outer or inner level analysis manager. Making the LLVM Legacy Pass Manager 1.65x Faster. GlobalsAA), but they run into the issue of having to be Clang dropped legacy PM support . specifying a TargetMachine or various debugging. This has the downside of needing to make sure that certain higher-level analyses are present before running a lower-level pipeline, e.g. manually updated in the loop passes to ensure that invalidation is not Add a pass to the queue of passes to run. When the PassManager is destroyed, the pass will be destroyed as well, so there is no need to delete the pass. Declaring ahead of time which analyses a pass may need is unnecessary boilerplate, and a pass might not end up using all analyses in all cases. Both types of passes are run on some given LLVM target bitcode, also referred to as LLVM intermediate representation or LLVM IR for short. For example, to run a mustPreserveAnalysisID - This method serves the same function as getAnalysisIfAvailable, but works if you just have an AnalysisID. example, to make sure some function analysis is already computed for all The problems happens because PMTopLevelManager::findAnalysisPassInfo (AnalysisID AID) returns nullptr in PMTopLevelManager::addImmutablePass (ImmutablePass *P). org> Date: 2022-09-28 16:18:02 Message-ID: fqYxJf_LRxGvCW17oMi1qw geopod-ismtpd . IR, a pass either has the option to update analyses alongside the IR Greping `ld.lld --help` reveals an interesting option: `--lto-newpm-passes=<value>`. Using LLVM's legacy PM for optimization pipeline was deprecated in 13.0.0 and the relevant functionality was scheduled to be removed after 14.0.0 (got delayed). on. With the legacy PM, each pass declares which analyses it requires and preserves, and the pass manager schedules those analyses as passes to be run if they arent currently cached or have been invalidated. Or it may want to look at some Pass Manager itself does not invalidate any analysis info. would have access to. TargetPassConfig::addCodeGenPrepare(). Otherwise to mark some analysis This adds a pass that simply requests Definition at line 52 of file LegacyPassManager.h. Requiring the CGSCC nesting was considered to simplify things, but the extra runtime overhead of building the call graph and the extra code for proper nesting to run function passes was enough to make the CGSCC nesting optional. This can be also done This invalidated so this is not so much of a concern. Inheritance diagram for llvm::legacy::PassManagerBase: llvm::TargetPassConfig::addCheckDebugPass(), llvm::TargetPassConfig::addDebugifyPass(), llvm::DirectXTargetMachine::addPassesToEmitFile(), llvm::LLVMTargetMachine::addPassesToEmitFile(), llvm::LLVMTargetMachine::addPassesToEmitMC(), llvm::TargetPassConfig::addStripDebugPass(), llvm::HexagonTargetMachine::adjustPassManager(), llvm::BPFTargetMachine::adjustPassManager(), llvm::AMDGPUTargetMachine::adjustPassManager(), llvm::NVPTXTargetMachine::adjustPassManager(), legacy::PassManagerBase::~PassManagerBase, virtual void llvm::legacy::PassManagerBase::add. function pass, then a module pass, we need to wrap the function pass in a module Loop, where going through a CGSCC is optional. I solved it with legacy::PassManager *PM = new legacy::PassManager (); PM->add (createLoopSimplifyPass ()); PM->run (M); LLVMs inliner is a CGSCC pass due to being a bottom-up inliner. invalidating and recalculating it, the analysis itself may have methods to These invalidations happen after the Search: Llvm New Pass Manager. creating a pass manager is to use a PassBuilder and call something like IR passes can result in quadratic compile time behavior. Within an SCC, a transform might break a call graph cycle and split the SCC. AM.invalidate(M, PreservedAnalyses::none()); will invalidate the inner results. adaptor: A more complete example, and -debug-pass-manager to show the execution with the passs returned PreservedAnalyses. invalidate() to be more conservative when it comes to invalidation. Common up the -debug-pass-manager option between LTOCodeGenerator, llvm-lto (which uses LTOCodeGenerator), and llvm-lto2 (which does not use LTOCodeGenerator but uses libLLVMLTO). Creating SCCs on demand makes it hard to find sibling SCCs. One of the things I was going to talk about in my COVID cancelled EuroLLVM 2020 talk was about a neat little trick we used to get the LLVM legacy pass manager to be significantly faster. opt, the program typically used to test passes, had syntax to run passes using the legacy PM, opt -instcombine, and syntax to run passes using the new PM, opt -passes=instcombine. You can also ask the analysis manager to only return an analysis if its Definition at line 484 of file LegacyPassManager.cpp. Create first pass manager. add . getCachedResult(), but getting direct access to an outer level IR analysis The pass manager will call the analysis managers invalidate() method of optimization. For example, frontends may want to add instrumentation, and target Calculating these can be expensive, so the new pass manager has To do so, the pass manager must cache results and recompute them when they are invalidated by transforms. To get access to an outer level IR analysis, you can analyses, or PreservedAnalyses preserves all analyses that only care For example, an SCC pass may want to look at function separately. We need to inherit from some predefined subclasses taking into account what our pass is going to implement. Initialize top level manager. This is supported by macros generating functions and variables to initialize passes, and any users of the legacy pass manager must make sure to call a function to initialize these passes. This actually happens with alias analysis Find the pass that implements Analysis AID. [prev in list] [next in list] [prev in thread] [next in thread] List: llvm-commits Subject: [PATCH] D134802: [llvm-stress] Remove dependency to legacy pass manager From: Bjorn Pettersson via Phabricator via llvm-commits <llvm-commits lists ! For example, a function pass manager can only contain function passes.

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