This implies that all passes MUST be allocated with 'new'. Although the pass manager infrastructure is not the only blocker, the legacy PM did have a couple of issues blocking parallelization. inner pass manager finishes, so accessing mutable analyses would give invalid So just in time for the legacy pass manager to finally sail off into the coding . // Clear the entry in the analysis manager for function F2 if we've completely removed it from the module. functions before a module pass: LLVM currently contains two pass managers, the legacy PM and the new PM. To use it, you need to include LegacyPassManager.h. dominator tree) should be shared between passes whenever possible for efficiency reasons, since recomputing analyses can be expensive. Closed Public. Take care in the pass to either clear the Now I have seen that LLVM has two PassManagers, a new one and an old one. Turning this on locally of course initially caused many tests to fail. For example, adding function passes after a module pass implicitly creates a function pass manager over a contiguous list of function passes. Set the initial size of the module if the user has specified that they want remarks for size. TargetPassConfig::addCodeGenPrepare(). At the call graph level, only sibling SCCs can be parallelized. P. ) inline. about the CFG, the FooAnalysisResult should not be invalidated. manager to compute an outer level IR analysis is not allowed. in TargetMachine::adjustPassManager() are part of the optimization Calculating these can be expensive, so the new pass manager has transformation, or tell the analysis manager that analyses are no longer So we need to keep the whole graph in memory to have something to use as a key. Currently The nesting is: module (-> cgscc) -> function -> loop, where the CGSCC nesting is optional. For example, a module llvm::legacy::PassManager Class Reference. run - Execute all of the passes scheduled for execution. Definition at line 479 of file LegacyPassManager.cpp. manually recomputed somewhere in the optimization pipeline if we want precision, added to a ModulePassManager: Generally you want to group CGSCC/function/loop passes together in a pass Just to list a couple: bugpoint, the LLVM C API, GPU divergence analysis. Loop passes often use function analyses such For . for more details. If passes The `llvm-lto` and `llvm-lto2` command line tools do support PassPlugin though -- but these tools are only intended for debug and development. 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. References llvm::createPrintModulePass(), and llvm::RISCVFenceField::O. 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. In these cases, the analysis manager can provide a This currently compiles esp xmm0 movsd esp eax eax esp ret We should use not the dag combiner This is because dagcombine2 needs to be able to see through the X86ISD::Wrapper which DAGCombine can t really do The code for turning x load into a single vector load is target independent and should be moved to the dag combiner The code for turning x load into a vector load can only handle a direct . For example, a function pass receives an analysis Upon inspection, some passes that were expected to be run in something like the -O2 pipeline werent being run. will call TargetMachine::registerPassBuilderCallbacks() to allow the Both types of passes are run on some given LLVM target bitcode, also referred to as LLVM intermediate representation or LLVM IR for short. Alias analysis is a function-level analysis, but there are Otherwise, it's, OuterAnalysisManagerProxy::Result::registerOuterAnalysisInvalidation(), 'no-op-module,cgscc(no-op-cgscc,function(no-op-function,loop(no-op-loop))),function(no-op-function,loop(no-op-loop))', 'function(no-op-function,no-op-function)', 'function(require),my-module-pass', Just Tell Me How To Run The Default Optimization Pipeline With The New Pass Manager, Status of the New and Legacy Pass Managers, If the first pass is not a module pass, a pass manager of the first pass is And some pipelines want to run a CGSCC pass independently of a function pass that comes right after, rather than nesting the function pass into the CGSCC pass via a CGSCC pass manager. To make tests using opt run against the new PM, we can either manually make them run twice, once against the legacy PM and once against the new PM, or we can automatically translate opt -instcombine to opt -passes=instcombine when the new PM is on by default. getPassID - Return the PassID number that corresponds to this pass. trigger outer level analysis computation could result in non-determinism if This passes ownership of the Pass to the PassManager. Or it may want to look at some function analyses in loop passes. runOnFunction for DominatorTree is called by pass manager before returning a reference to . they are LLVM IR passes (whereas all MIR passes are codegen passes). couple reasons. passes which work on a fixed scope. Diff Detail analyses for the functions inside the SCC. Currently the new PM applies only to the middle-end optimization pipeline working with LLVM IR. HelloWorld.cpp: Analyses (e.g. And if we have a persistent call graph, we need to make sure it is up to date if passes change its structure. Diff Detail cases, PassBuilder exposes callbacks that allow injecting passes into There are a couple of special cases for easier typing: For a list of available passes and analyses, including the IR unit (module, 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). The pass manager makes sure we visit SCCs bottom-up so that callees are as optimized as possible when we get to their callers and callers have as precise information as possible. this wouldnt be an issue, but that would be a lot of work to ensure every pass The legacy PM did not support retrieval of analyses for arbitrary functions in a CGSCC pass. creating a pass manager is to use a PassBuilder and call something like When the PassManager is destroyed, the pass will be destroyed as well, so there is no need to delete the pass. Definition at line 468 of file LegacyPassManager.cpp. The pass manager tells the analysis manager to handle invalidated cached analyses. When the PassManager is destroyed, the pass will be destroyed as well, so there is no need to delete the pass. -load-pass-plugin=path/to/plugin.so loads a pass plugin into opt. However, the typical use case is to run a predetermined pass pipeline. mustPreserveAnalysisID - This method serves the same function as getAnalysisIfAvailable, but works if you just have an AnalysisID. cached/invalidated, you can mark the analysis manager proxy as preserved, Rather than having the pass manager take care of analyses, a separate analysis manager is in charge of computing, caching, and invalidating analyses. Pass Manager itself does not invalidate any analysis info. Actions. This is the complete list of members for llvm::legacy::PassManagerImpl, including all inherited members. as the dominator tree. the optimization pipeline. The typical way to invalidate analysis results is for a pass to declare what includes anything added via TargetPassConfig hooks, e.g. When the PassManager is destroyed, the pass will be destroyed as well, so there is no need to delete the pass. FunctionAnalysisManager from a CGSCCAnalysisManager, you can call, and use FAM as a typical FunctionAnalysisManager that a function pass To use the legacy pass manager with opt, pass the -enable-new-pm=0 flag to all opt invocations. // We haven't made any control flow changes, any analyses that only care about the control flow are still valid. analyses, or PreservedAnalyses preserves all analyses that only care making sure GlobalsAA has been computed before running a function pipeline. When a pass runs on some IR, it also receives an analysis manager which it can query for analyses. optimization pipeline (aka the middle-end) works with both the legacy PM and remove its usage. level pass manager. results for that function or not use inner analyses at all. Edit Revision; Update Diff; Download Raw Diff; . Find the pass that implements Analysis AID. The C API also supports most of this, see llvm-c/Transforms/PassBuilder.h. any existing inner proxies. essentially saying that all deleted entries have been taken care of manually. Since passes can ask for a cached analysis result, allowing passes to Asking for a cached and immutable outer level IR analysis works via void llvm::legacy::FunctionPassManagerImpl::add. Otherwise to mark some analysis pass on each one. manually updated in the loop passes to ensure that invalidation is not This is the reason behind the complexity of the CGSCC pass manager in the new PM. It includes PassManager to manage module pass and FunctionPassManager to manage FunctionPasses. For example, a FunctionPassManager References M, and llvm::legacy::PassManagerImpl::run(). FunctionPassManager, the loop pass must be wrapped in a function pass will run FunctionPass1 on each function in a module, then run // Invalidate all analysis results for function F1. compile times as low as possible. To add a pass to a new PM pass manager, the important thing is to match the pipeline, and should have a corresponding line in add . I appreciate your response. Since analyses are handled by an analysis manager in the new PM, the analysis manager can cache arbitrary analyses for arbitrary functions. updates all outer level analyses, and so far this hasnt been necessary and References assert(), N, and llvm::PMTopLevelManager::PassManagers. Member Function Documentation add () Add a pass to the queue of passes to run. doFinalization - Virtual method overriden by subclasses to do any necessary clean up after all passes have run. This is for a comes from trying to invalidate as few analysis results as possible to keep Scheduling can be simple, such as running a list of module passes, or running function passes on every function inside a module. TargetMachine::registerPassBuilderCallbacks(). rGb0f7f6f78d05: [mlir] Remove uses of LLVM's legacy pass manager Summary Use the new pass manager. However, a vast majority of LLVM tests were still only testing the legacy PM. Consider the following SCC containing two functions. managers created by that PassBuilder. Generally for outer proxies, analysis results from the outer analysis manager manually within the pass: One thing to note when accessing inner level IR analyses is cached results for // We've made transformations and don't want to bother to update any analyses. Created using, // Take a look at the PassBuilder constructor parameters for more, // customization, e.g. Since the legacy PM modelled analyses as passes to be scheduled and run, we cant efficiently access analyses to arbitrary functions. If a pass wants to keep some specific LLVM Project News and Details from the Trenches. there isnt infrastructure for this (aside from function analyses in loop passes For example, all Clang tests had been passing with the new PM for a while. For how to write a new PM pass, see this page. This may even destroy the pass right away if it is found to be redundant. The analysis manager only provides analysis results for the same IR type as Module analyses can be computed from function passes in the legacy PM. LLVM currently has two separate pass managers: the legacy pass manager (legacy PM) and the new pass manager (new PM). Although there has been work to start making the codegen pipeline work with the new PM, it is still very far from being usable. The starting point for LLVM passes is the Pass class, which is a superclass of all the passes. will run FunctionPass1 and FunctionPass2 on the first function in a Otherwise the proxy The legacy CGSCC pass manager would simply move on to the next part of the call graph. This may even destroy the pass right away if it is found to be redundant. Add RequiredPass into list of lower level passes required by pass P. Initialize available analysis information. contain pointers to IR that is no longer valid, meaning that the inner proxy Please file bugs for any regressions. An analysis can implement So as part of the new PMs incremental call graph update, if an SCC is split, we make sure to visit the newly split SCCs bottom-up. Does the <value> here mean built-in pass names like `dce`/`mem2reg`, information on writing a pass plugin, see Writing an LLVM Pass. But we need some way for a pass manager builder to be aware of all passes for testing purposes. These invalidations happen after the See ( #include "llvm/IR/LegacyPassManager.h") llvm::PassManager is actually a class template. Women in Compilers and Tools Meetup Series, Various target-specific tests were failing. PassManagerImpl manages MPPassManagers. The BasicBlockManager was improperly tested and found to be potentially broken, and was deprecated as of rL373254. We now want to revisit foo since we have better information, most notably that foo is in its own SCC. Normally a tutorial for writing a (legacy) LLVM Pass would start with telling you to write a class which inherits one of the llvm::Pass family, llvm::FunctionPass for example, then implemented . For example, opt 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. 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. This implies that all passes MUST be allocated with 'new'. Separately, Chrome recently started using PGO and ThinLTO to make Chrome faster, each with noticeable performance wins. For example, clang -O2 runs a predetermined set of passes on the input IR. You can also ask the analysis manager to only return an analysis if its For that, I want to utilize several analysis passes but not from a pass context. when results are no longer valid. Definition at line 39 of file LegacyPassManager.h. For example, running all loop passes on a loop may cause a // We've specifically updated the dominator tree alongside any transformations, but other analysis results may be invalid. analyses have access to which is passed into loop passes as a results. Initialize top level manager. analysis manager proxy which will clear all cached analyses, conservatively However, if youd like to be more selective about which analyses are PassBuilder::buildPerModuleDefaultPipeline() which creates a typical It does not use the legacy pass manager. Calculating these can be expensive, so the new pass manager has infrastructure to cache analyses and reuse them when possible. adaptor: A more complete example, and -debug-pass-manager to show the execution In my. I noticed throughout the project that even though I would have really liked to rewrite my pass using the new pass manager I could not invest that much time. as described below). Loop, where going through a CGSCC is optional. says that if the PreservedAnalyses specifically preserves The IR nesting in the new PM is module (-> CGSCC) -> function -> loop, where the CGSCC nesting is optional. Other options, like debugging the execution of a pass manager, are also specified via the constructor, and not through a global flag. Then hopefully at some point we can start to remove parts of the optimization pipeline that are legacy PM-specific. To make sure an analysis named foo is available before a pass, add Referenced by codegen(), llvm::MCJIT::emitObject(), llvm::lintModule(), and llvm::orc::SimpleCompiler::operator()(). This is better for cache locality around LLVM data structures. invalidate() to be more conservative when it comes to invalidation. Users of a pass manager builder can add plugins that register parsing callbacks to handle custom out-of-tree passes. When transforming As mentioned before, passes added While we cant yet remove the legacy pass manager, we can start the deprecation of it, at least for the optimization pipeline. This pass is also subject to proper nesting. This because PassRegistry::getPassRegistry ()->getPassInfo (AID) call in it returns nullptr as well. The legacy PM has been in use for a very long time and did its job fairly well. Self-updating analyses that gracefully degrade also handle Populate UsedPasses with analysis pass that are used or required by pass P and are available. AM.invalidate(M, PreservedAnalyses::none()); will invalidate the inner (. as the key for cached analyses. Reimplemented in llvm::DebugifyCustomPassManager. However, it is with the passs returned PreservedAnalyses. This has the downside of needing to make sure that certain higher-level analyses are present before running a lower-level pipeline, e.g. P. ) inline. Definition at line 1665 of file LegacyPassManager.cpp. Some IR passes are considered part of the backend codegen pipeline even if would have access to. Definition at line 524 of file LegacyPassManager.cpp. There are two ways to deal with potentially invalid analysis results. immutable global analysis. One is Needs investigation. Otherwise it will construct a When the PassManager is destroyed, the pass will be destroyed as well, so there is no need to delete the pass. For should be immutable, so invalidation shouldnt be a concern. Add a pass to the queue of passes to run. Outer analyses unused by inner passes can and often will be The first reason is that running analyses across outer level IR in inner level 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). could keep outer level analyses up to date rather than computing them on demand When the PassManager is destroyed, the pass will be destroyed as well, so there is no need to delete the pass. To get access to an outer level IR analysis, you can order: Improper nesting can lead to error messages such as. There were some efforts upstream to make the new PM work for all use cases. getAdjustedAnalysisPointer - This method is used when a pass implements an analysis interface through multiple inheritance. adaptor that goes through all the loops in the function and runs the loop example, a FunctionPassManager is a function pass, meaning it can be Clang dropped legacy PM support . However, there were some missing features required for better optimization opportunities, most notably the ability to use function analysis results for arbitrary functions from the inliner. When a pass runs on some IR, it also receives an analysis manager which it can For example, a function valid and should be invalidated. The backend codegen pipeline still works only with the legacy PM, mostly because most codegen passes dont work on LLVM IR, but rather machine IR (MIR), and nobody has yet put in the time to create the new PM infrastructure for MIR passes and to migrate all of the backends to use the new PM. We can manually create analyses for other functions, but they wont be cached anywhere, leading to lots of redundant work and unacceptable compile time regressions. results. PMs TargetMachine::adjustPassManager(). For example, a function pass manager can only contain function passes. To avoid too much redundant work regenerating a potentially large but sparse graph, we need to incrementally update the graph. For more details, see Writing an LLVM Pass and Using the New Pass Manager. example, to make sure some function analysis is already computed for all C++ source code API documentation for LLVM. types of analyses it preserves and what types it does not. in PAC.preserved()), or if PreservedAnalyses preserves all function if the proxy itself should be invalidated. can only contain function passes: If you want to add a loop pass that runs on all loops in a function to a However, some passes want to peek up or Find analysis usage information for the pass P. isPassDebuggingExecutionsOrMore - Return true if -debug-pass=Executions or higher is specified. Rather than manually adding passes to a pass manager, the typical way of Scheduling can also be more involved, such as making sure we visit SCCs in the call graph in the correct order. However, the legacy CGSCC pass manager only stored the functions in the current SCC in memory and did not have a persistent call graph data structure to use as keys to cache analyses. PassBuilder::buildPerModuleDefaultPipeline(), TargetMachine::registerPassBuilderCallbacks(), AMDGPUTargetMachine::registerPassBuilderCallbacks(). 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. it has already computed the result for the requested IR. Inheritance diagram for llvm::legacy::PassManagerImpl: Collaboration diagram for llvm::legacy::PassManagerImpl: llvm::PMTopLevelManager::getImmutablePasses(), llvm::PMTopLevelManager::getNumContainedManagers(), llvm::PMTopLevelManager::initializeAllAnalysisInfo(). PassBuilder for the various places that passes can be added. By inheriting this class we allow the entire module to be analyzed at once. When referring to "legacy PM" and "new PM", this includes all of the surrounding infrastructure, not just the entity that manages passes. For example, an SCC pass may want to look at function A pass manager schedules transformation passes and analyses to be run on IR in a specific order. It turns out that the new PM CGSCC infrastructure didnt support extracting parts of a function into another (aka outlining) in a CGSCC pass. Add a pass to the queue of passes to run. . Definition at line 484 of file LegacyPassManager.cpp. Sep 20 2021, 12:56 PM. Making the LLVM Legacy Pass Manager 1.65x Faster. For things like functions and loops, we have persistent data structures for those to use as keys. The exception to not being able to access outer level analyses is accessing manager, that is implicitly created. In order for a pass to communicate that analyses have been invalidated, it returns which analyses it has preserved.
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