//===- CGSCCPassManager.h - Call graph pass management ----------*- C++ -*-===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// /// \file /// /// This header provides classes for managing passes over SCCs of the call /// graph. These passes form an important component of LLVM's interprocedural /// optimizations. Because they operate on the SCCs of the call graph, and they /// traverse the graph in post-order, they can effectively do pair-wise /// interprocedural optimizations for all call edges in the program while /// incrementally refining it and improving the context of these pair-wise /// optimizations. At each call site edge, the callee has already been /// optimized as much as is possible. This in turn allows very accurate /// analysis of it for IPO. /// /// A secondary more general goal is to be able to isolate optimization on /// unrelated parts of the IR module. This is useful to ensure our /// optimizations are principled and don't miss oportunities where refinement /// of one part of the module influence transformations in another part of the /// module. But this is also useful if we want to parallelize the optimizations /// across common large module graph shapes which tend to be very wide and have /// large regions of unrelated cliques. /// /// To satisfy these goals, we use the LazyCallGraph which provides two graphs /// nested inside each other (and built lazily from the bottom-up): the call /// graph proper, and a reference graph. The reference graph is super set of /// the call graph and is a conservative approximation of what could through /// scalar or CGSCC transforms *become* the call graph. Using this allows us to /// ensure we optimize functions prior to them being introduced into the call /// graph by devirtualization or other technique, and thus ensures that /// subsequent pair-wise interprocedural optimizations observe the optimized /// form of these functions. The (potentially transitive) reference /// reachability used by the reference graph is a conservative approximation /// that still allows us to have independent regions of the graph. /// /// FIXME: There is one major drawback of the reference graph: in its naive /// form it is quadratic because it contains a distinct edge for each /// (potentially indirect) reference, even if are all through some common /// global table of function pointers. This can be fixed in a number of ways /// that essentially preserve enough of the normalization. While it isn't /// expected to completely preclude the usability of this, it will need to be /// addressed. /// /// /// All of these issues are made substantially more complex in the face of /// mutations to the call graph while optimization passes are being run. When /// mutations to the call graph occur we want to achieve two different things: /// /// - We need to update the call graph in-flight and invalidate analyses /// cached on entities in the graph. Because of the cache-based analysis /// design of the pass manager, it is essential to have stable identities for /// the elements of the IR that passes traverse, and to invalidate any /// analyses cached on these elements as the mutations take place. /// /// - We want to preserve the incremental and post-order traversal of the /// graph even as it is refined and mutated. This means we want optimization /// to observe the most refined form of the call graph and to do so in /// post-order. /// /// To address this, the CGSCC manager uses both worklists that can be expanded /// by passes which transform the IR, and provides invalidation tests to skip /// entries that become dead. This extra data is provided to every SCC pass so /// that it can carefully update the manager's traversal as the call graph /// mutates. /// /// We also provide support for running function passes within the CGSCC walk, /// and there we provide automatic update of the call graph including of the /// pass manager to reflect call graph changes that fall out naturally as part /// of scalar transformations. /// /// The patterns used to ensure the goals of post-order visitation of the fully /// refined graph: /// /// 1) Sink toward the "bottom" as the graph is refined. This means that any /// iteration continues in some valid post-order sequence after the mutation /// has altered the structure. /// /// 2) Enqueue in post-order, including the current entity. If the current /// entity's shape changes, it and everything after it in post-order needs /// to be visited to observe that shape. /// //===----------------------------------------------------------------------===// #ifndef LLVM_ANALYSIS_CGSCCPASSMANAGER_H #define LLVM_ANALYSIS_CGSCCPASSMANAGER_H #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/DenseSet.h" #include "llvm/ADT/MapVector.h" #include "llvm/ADT/PriorityWorklist.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallVector.h" #include "llvm/Analysis/LazyCallGraph.h" #include "llvm/IR/Function.h" #include "llvm/IR/InstIterator.h" #include "llvm/IR/PassManager.h" #include "llvm/IR/ValueHandle.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" #include #include #include namespace llvm { struct CGSCCUpdateResult; class Module; // Allow debug logging in this inline function. #define DEBUG_TYPE "cgscc" /// Extern template declaration for the analysis set for this IR unit. extern template class AllAnalysesOn; extern template class AnalysisManager; /// The CGSCC analysis manager. /// /// See the documentation for the AnalysisManager template for detail /// documentation. This type serves as a convenient way to refer to this /// construct in the adaptors and proxies used to integrate this into the larger /// pass manager infrastructure. using CGSCCAnalysisManager = AnalysisManager; // Explicit specialization and instantiation declarations for the pass manager. // See the comments on the definition of the specialization for details on how // it differs from the primary template. template <> PreservedAnalyses PassManager::run(LazyCallGraph::SCC &InitialC, CGSCCAnalysisManager &AM, LazyCallGraph &G, CGSCCUpdateResult &UR); extern template class PassManager; /// The CGSCC pass manager. /// /// See the documentation for the PassManager template for details. It runs /// a sequence of SCC passes over each SCC that the manager is run over. This /// type serves as a convenient way to refer to this construct. using CGSCCPassManager = PassManager; /// An explicit specialization of the require analysis template pass. template struct RequireAnalysisPass : PassInfoMixin> { PreservedAnalyses run(LazyCallGraph::SCC &C, CGSCCAnalysisManager &AM, LazyCallGraph &CG, CGSCCUpdateResult &) { (void)AM.template getResult(C, CG); return PreservedAnalyses::all(); } }; /// A proxy from a \c CGSCCAnalysisManager to a \c Module. using CGSCCAnalysisManagerModuleProxy = InnerAnalysisManagerProxy; /// We need a specialized result for the \c CGSCCAnalysisManagerModuleProxy so /// it can have access to the call graph in order to walk all the SCCs when /// invalidating things. template <> class CGSCCAnalysisManagerModuleProxy::Result { public: explicit Result(CGSCCAnalysisManager &InnerAM, LazyCallGraph &G) : InnerAM(&InnerAM), G(&G) {} /// Accessor for the analysis manager. CGSCCAnalysisManager &getManager() { return *InnerAM; } /// Handler for invalidation of the Module. /// /// If the proxy analysis itself is preserved, then we assume that the set of /// SCCs in the Module hasn't changed. Thus any pointers to SCCs in the /// CGSCCAnalysisManager are still valid, and we don't need to call \c clear /// on the CGSCCAnalysisManager. /// /// Regardless of whether this analysis is marked as preserved, all of the /// analyses in the \c CGSCCAnalysisManager are potentially invalidated based /// on the set of preserved analyses. bool invalidate(Module &M, const PreservedAnalyses &PA, ModuleAnalysisManager::Invalidator &Inv); private: CGSCCAnalysisManager *InnerAM; LazyCallGraph *G; }; /// Provide a specialized run method for the \c CGSCCAnalysisManagerModuleProxy /// so it can pass the lazy call graph to the result. template <> CGSCCAnalysisManagerModuleProxy::Result CGSCCAnalysisManagerModuleProxy::run(Module &M, ModuleAnalysisManager &AM); // Ensure the \c CGSCCAnalysisManagerModuleProxy is provided as an extern // template. extern template class InnerAnalysisManagerProxy; extern template class OuterAnalysisManagerProxy< ModuleAnalysisManager, LazyCallGraph::SCC, LazyCallGraph &>; /// A proxy from a \c ModuleAnalysisManager to an \c SCC. using ModuleAnalysisManagerCGSCCProxy = OuterAnalysisManagerProxy; /// Support structure for SCC passes to communicate updates the call graph back /// to the CGSCC pass manager infrsatructure. /// /// The CGSCC pass manager runs SCC passes which are allowed to update the call /// graph and SCC structures. This means the structure the pass manager works /// on is mutating underneath it. In order to support that, there needs to be /// careful communication about the precise nature and ramifications of these /// updates to the pass management infrastructure. /// /// All SCC passes will have to accept a reference to the management layer's /// update result struct and use it to reflect the results of any CG updates /// performed. /// /// Passes which do not change the call graph structure in any way can just /// ignore this argument to their run method. struct CGSCCUpdateResult { /// Worklist of the RefSCCs queued for processing. /// /// When a pass refines the graph and creates new RefSCCs or causes them to /// have a different shape or set of component SCCs it should add the RefSCCs /// to this worklist so that we visit them in the refined form. /// /// This worklist is in reverse post-order, as we pop off the back in order /// to observe RefSCCs in post-order. When adding RefSCCs, clients should add /// them in reverse post-order. SmallPriorityWorklist &RCWorklist; /// Worklist of the SCCs queued for processing. /// /// When a pass refines the graph and creates new SCCs or causes them to have /// a different shape or set of component functions it should add the SCCs to /// this worklist so that we visit them in the refined form. /// /// Note that if the SCCs are part of a RefSCC that is added to the \c /// RCWorklist, they don't need to be added here as visiting the RefSCC will /// be sufficient to re-visit the SCCs within it. /// /// This worklist is in reverse post-order, as we pop off the back in order /// to observe SCCs in post-order. When adding SCCs, clients should add them /// in reverse post-order. SmallPriorityWorklist &CWorklist; /// The set of invalidated RefSCCs which should be skipped if they are found /// in \c RCWorklist. /// /// This is used to quickly prune out RefSCCs when they get deleted and /// happen to already be on the worklist. We use this primarily to avoid /// scanning the list and removing entries from it. SmallPtrSetImpl &InvalidatedRefSCCs; /// The set of invalidated SCCs which should be skipped if they are found /// in \c CWorklist. /// /// This is used to quickly prune out SCCs when they get deleted and happen /// to already be on the worklist. We use this primarily to avoid scanning /// the list and removing entries from it. SmallPtrSetImpl &InvalidatedSCCs; /// If non-null, the updated current \c RefSCC being processed. /// /// This is set when a graph refinement takes place an the "current" point in /// the graph moves "down" or earlier in the post-order walk. This will often /// cause the "current" RefSCC to be a newly created RefSCC object and the /// old one to be added to the above worklist. When that happens, this /// pointer is non-null and can be used to continue processing the "top" of /// the post-order walk. LazyCallGraph::RefSCC *UpdatedRC; /// If non-null, the updated current \c SCC being processed. /// /// This is set when a graph refinement takes place an the "current" point in /// the graph moves "down" or earlier in the post-order walk. This will often /// cause the "current" SCC to be a newly created SCC object and the old one /// to be added to the above worklist. When that happens, this pointer is /// non-null and can be used to continue processing the "top" of the /// post-order walk. LazyCallGraph::SCC *UpdatedC; /// Preserved analyses across SCCs. /// /// We specifically want to allow CGSCC passes to mutate ancestor IR /// (changing both the CG structure and the function IR itself). However, /// this means we need to take special care to correctly mark what analyses /// are preserved *across* SCCs. We have to track this out-of-band here /// because within the main `PassManeger` infrastructure we need to mark /// everything within an SCC as preserved in order to avoid repeatedly /// invalidating the same analyses as we unnest pass managers and adaptors. /// So we track the cross-SCC version of the preserved analyses here from any /// code that does direct invalidation of SCC analyses, and then use it /// whenever we move forward in the post-order walk of SCCs before running /// passes over the new SCC. PreservedAnalyses CrossSCCPA; /// A hacky area where the inliner can retain history about inlining /// decisions that mutated the call graph's SCC structure in order to avoid /// infinite inlining. See the comments in the inliner's CG update logic. /// /// FIXME: Keeping this here seems like a big layering issue, we should look /// for a better technique. SmallDenseSet, 4> &InlinedInternalEdges; /// Weak VHs to keep track of indirect calls for the purposes of detecting /// devirtualization. /// /// This is a map to avoid having duplicate entries. If a Value is /// deallocated, its corresponding WeakTrackingVH will be nulled out. When /// checking if a Value is in the map or not, also check if the corresponding /// WeakTrackingVH is null to avoid issues with a new Value sharing the same /// address as a deallocated one. SmallMapVector IndirectVHs; }; /// The core module pass which does a post-order walk of the SCCs and /// runs a CGSCC pass over each one. /// /// Designed to allow composition of a CGSCCPass(Manager) and /// a ModulePassManager. Note that this pass must be run with a module analysis /// manager as it uses the LazyCallGraph analysis. It will also run the /// \c CGSCCAnalysisManagerModuleProxy analysis prior to running the CGSCC /// pass over the module to enable a \c FunctionAnalysisManager to be used /// within this run safely. class ModuleToPostOrderCGSCCPassAdaptor : public PassInfoMixin { public: using PassConceptT = detail::PassConcept; explicit ModuleToPostOrderCGSCCPassAdaptor(std::unique_ptr Pass) : Pass(std::move(Pass)) {} ModuleToPostOrderCGSCCPassAdaptor(ModuleToPostOrderCGSCCPassAdaptor &&Arg) : Pass(std::move(Arg.Pass)) {} friend void swap(ModuleToPostOrderCGSCCPassAdaptor &LHS, ModuleToPostOrderCGSCCPassAdaptor &RHS) { std::swap(LHS.Pass, RHS.Pass); } ModuleToPostOrderCGSCCPassAdaptor & operator=(ModuleToPostOrderCGSCCPassAdaptor RHS) { swap(*this, RHS); return *this; } /// Runs the CGSCC pass across every SCC in the module. PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM); static bool isRequired() { return true; } private: std::unique_ptr Pass; }; /// A function to deduce a function pass type and wrap it in the /// templated adaptor. template ModuleToPostOrderCGSCCPassAdaptor createModuleToPostOrderCGSCCPassAdaptor(CGSCCPassT Pass) { using PassModelT = detail::PassModel; return ModuleToPostOrderCGSCCPassAdaptor( std::make_unique(std::move(Pass))); } /// A proxy from a \c FunctionAnalysisManager to an \c SCC. /// /// When a module pass runs and triggers invalidation, both the CGSCC and /// Function analysis manager proxies on the module get an invalidation event. /// We don't want to fully duplicate responsibility for most of the /// invalidation logic. Instead, this layer is only responsible for SCC-local /// invalidation events. We work with the module's FunctionAnalysisManager to /// invalidate function analyses. class FunctionAnalysisManagerCGSCCProxy : public AnalysisInfoMixin { public: class Result { public: explicit Result() : FAM(nullptr) {} explicit Result(FunctionAnalysisManager &FAM) : FAM(&FAM) {} void updateFAM(FunctionAnalysisManager &FAM) { this->FAM = &FAM; } /// Accessor for the analysis manager. FunctionAnalysisManager &getManager() { assert(FAM); return *FAM; } bool invalidate(LazyCallGraph::SCC &C, const PreservedAnalyses &PA, CGSCCAnalysisManager::Invalidator &Inv); private: FunctionAnalysisManager *FAM; }; /// Computes the \c FunctionAnalysisManager and stores it in the result proxy. Result run(LazyCallGraph::SCC &C, CGSCCAnalysisManager &AM, LazyCallGraph &); private: friend AnalysisInfoMixin; static AnalysisKey Key; }; extern template class OuterAnalysisManagerProxy; /// A proxy from a \c CGSCCAnalysisManager to a \c Function. using CGSCCAnalysisManagerFunctionProxy = OuterAnalysisManagerProxy; /// Helper to update the call graph after running a function pass. /// /// Function passes can only mutate the call graph in specific ways. This /// routine provides a helper that updates the call graph in those ways /// including returning whether any changes were made and populating a CG /// update result struct for the overall CGSCC walk. LazyCallGraph::SCC &updateCGAndAnalysisManagerForFunctionPass( LazyCallGraph &G, LazyCallGraph::SCC &C, LazyCallGraph::Node &N, CGSCCAnalysisManager &AM, CGSCCUpdateResult &UR, FunctionAnalysisManager &FAM); /// Helper to update the call graph after running a CGSCC pass. /// /// CGSCC passes can only mutate the call graph in specific ways. This /// routine provides a helper that updates the call graph in those ways /// including returning whether any changes were made and populating a CG /// update result struct for the overall CGSCC walk. LazyCallGraph::SCC &updateCGAndAnalysisManagerForCGSCCPass( LazyCallGraph &G, LazyCallGraph::SCC &C, LazyCallGraph::Node &N, CGSCCAnalysisManager &AM, CGSCCUpdateResult &UR, FunctionAnalysisManager &FAM); /// Adaptor that maps from a SCC to its functions. /// /// Designed to allow composition of a FunctionPass(Manager) and /// a CGSCCPassManager. Note that if this pass is constructed with a pointer /// to a \c CGSCCAnalysisManager it will run the /// \c FunctionAnalysisManagerCGSCCProxy analysis prior to running the function /// pass over the SCC to enable a \c FunctionAnalysisManager to be used /// within this run safely. class CGSCCToFunctionPassAdaptor : public PassInfoMixin { public: using PassConceptT = detail::PassConcept; explicit CGSCCToFunctionPassAdaptor(std::unique_ptr Pass) : Pass(std::move(Pass)) {} CGSCCToFunctionPassAdaptor(CGSCCToFunctionPassAdaptor &&Arg) : Pass(std::move(Arg.Pass)) {} friend void swap(CGSCCToFunctionPassAdaptor &LHS, CGSCCToFunctionPassAdaptor &RHS) { std::swap(LHS.Pass, RHS.Pass); } CGSCCToFunctionPassAdaptor &operator=(CGSCCToFunctionPassAdaptor RHS) { swap(*this, RHS); return *this; } /// Runs the function pass across every function in the module. PreservedAnalyses run(LazyCallGraph::SCC &C, CGSCCAnalysisManager &AM, LazyCallGraph &CG, CGSCCUpdateResult &UR); static bool isRequired() { return true; } private: std::unique_ptr Pass; }; /// A function to deduce a function pass type and wrap it in the /// templated adaptor. template CGSCCToFunctionPassAdaptor createCGSCCToFunctionPassAdaptor(FunctionPassT Pass) { using PassModelT = detail::PassModel; return CGSCCToFunctionPassAdaptor( std::make_unique(std::move(Pass))); } /// A helper that repeats an SCC pass each time an indirect call is refined to /// a direct call by that pass. /// /// While the CGSCC pass manager works to re-visit SCCs and RefSCCs as they /// change shape, we may also want to repeat an SCC pass if it simply refines /// an indirect call to a direct call, even if doing so does not alter the /// shape of the graph. Note that this only pertains to direct calls to /// functions where IPO across the SCC may be able to compute more precise /// results. For intrinsics, we assume scalar optimizations already can fully /// reason about them. /// /// This repetition has the potential to be very large however, as each one /// might refine a single call site. As a consequence, in practice we use an /// upper bound on the number of repetitions to limit things. class DevirtSCCRepeatedPass : public PassInfoMixin { public: using PassConceptT = detail::PassConcept; explicit DevirtSCCRepeatedPass(std::unique_ptr Pass, int MaxIterations) : Pass(std::move(Pass)), MaxIterations(MaxIterations) {} /// Runs the wrapped pass up to \c MaxIterations on the SCC, iterating /// whenever an indirect call is refined. PreservedAnalyses run(LazyCallGraph::SCC &InitialC, CGSCCAnalysisManager &AM, LazyCallGraph &CG, CGSCCUpdateResult &UR); private: std::unique_ptr Pass; int MaxIterations; }; /// A function to deduce a function pass type and wrap it in the /// templated adaptor. template DevirtSCCRepeatedPass createDevirtSCCRepeatedPass(CGSCCPassT Pass, int MaxIterations) { using PassModelT = detail::PassModel; return DevirtSCCRepeatedPass(std::make_unique(std::move(Pass)), MaxIterations); } // Clear out the debug logging macro. #undef DEBUG_TYPE } // end namespace llvm #endif // LLVM_ANALYSIS_CGSCCPASSMANAGER_H