llvm-6502/include/llvm/Analysis/LazyCallGraph.h
Chandler Carruth c9109225e2 Revert r225854: [PM] Move the LazyCallGraph printing functionality to
a print method.

This was formulated on a bad idea, but sadly I didn't uncover how bad
this was until I got further down the path. I had hoped that we could
provide a low boilerplate way of printing analyses, but it just doesn't
seem like this really fits the needs of the analyses. Not all analyses
really want to do printing, and those that do don't all use the same
interface. Instead, with the new pass manager let's just take advantage
of the fact that creating an explicit printer pass like the LCG has is
pretty low boilerplate already and rely on that for testing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225861 91177308-0d34-0410-b5e6-96231b3b80d8
2015-01-14 00:27:45 +00:00

575 lines
22 KiB
C++

//===- LazyCallGraph.h - Analysis of a Module's call graph ------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
/// \file
///
/// Implements a lazy call graph analysis and related passes for the new pass
/// manager.
///
/// NB: This is *not* a traditional call graph! It is a graph which models both
/// the current calls and potential calls. As a consequence there are many
/// edges in this call graph that do not correspond to a 'call' or 'invoke'
/// instruction.
///
/// The primary use cases of this graph analysis is to facilitate iterating
/// across the functions of a module in ways that ensure all callees are
/// visited prior to a caller (given any SCC constraints), or vice versa. As
/// such is it particularly well suited to organizing CGSCC optimizations such
/// as inlining, outlining, argument promotion, etc. That is its primary use
/// case and motivates the design. It may not be appropriate for other
/// purposes. The use graph of functions or some other conservative analysis of
/// call instructions may be interesting for optimizations and subsequent
/// analyses which don't work in the context of an overly specified
/// potential-call-edge graph.
///
/// To understand the specific rules and nature of this call graph analysis,
/// see the documentation of the \c LazyCallGraph below.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_LAZYCALLGRAPH_H
#define LLVM_ANALYSIS_LAZYCALLGRAPH_H
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/iterator.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Support/Allocator.h"
#include <iterator>
namespace llvm {
class PreservedAnalyses;
class raw_ostream;
/// \brief A lazily constructed view of the call graph of a module.
///
/// With the edges of this graph, the motivating constraint that we are
/// attempting to maintain is that function-local optimization, CGSCC-local
/// optimizations, and optimizations transforming a pair of functions connected
/// by an edge in the graph, do not invalidate a bottom-up traversal of the SCC
/// DAG. That is, no optimizations will delete, remove, or add an edge such
/// that functions already visited in a bottom-up order of the SCC DAG are no
/// longer valid to have visited, or such that functions not yet visited in
/// a bottom-up order of the SCC DAG are not required to have already been
/// visited.
///
/// Within this constraint, the desire is to minimize the merge points of the
/// SCC DAG. The greater the fanout of the SCC DAG and the fewer merge points
/// in the SCC DAG, the more independence there is in optimizing within it.
/// There is a strong desire to enable parallelization of optimizations over
/// the call graph, and both limited fanout and merge points will (artificially
/// in some cases) limit the scaling of such an effort.
///
/// To this end, graph represents both direct and any potential resolution to
/// an indirect call edge. Another way to think about it is that it represents
/// both the direct call edges and any direct call edges that might be formed
/// through static optimizations. Specifically, it considers taking the address
/// of a function to be an edge in the call graph because this might be
/// forwarded to become a direct call by some subsequent function-local
/// optimization. The result is that the graph closely follows the use-def
/// edges for functions. Walking "up" the graph can be done by looking at all
/// of the uses of a function.
///
/// The roots of the call graph are the external functions and functions
/// escaped into global variables. Those functions can be called from outside
/// of the module or via unknowable means in the IR -- we may not be able to
/// form even a potential call edge from a function body which may dynamically
/// load the function and call it.
///
/// This analysis still requires updates to remain valid after optimizations
/// which could potentially change the set of potential callees. The
/// constraints it operates under only make the traversal order remain valid.
///
/// The entire analysis must be re-computed if full interprocedural
/// optimizations run at any point. For example, globalopt completely
/// invalidates the information in this analysis.
///
/// FIXME: This class is named LazyCallGraph in a lame attempt to distinguish
/// it from the existing CallGraph. At some point, it is expected that this
/// will be the only call graph and it will be renamed accordingly.
class LazyCallGraph {
public:
class Node;
class SCC;
typedef SmallVector<PointerUnion<Function *, Node *>, 4> NodeVectorT;
typedef SmallVectorImpl<PointerUnion<Function *, Node *>> NodeVectorImplT;
/// \brief A lazy iterator used for both the entry nodes and child nodes.
///
/// When this iterator is dereferenced, if not yet available, a function will
/// be scanned for "calls" or uses of functions and its child information
/// will be constructed. All of these results are accumulated and cached in
/// the graph.
class iterator
: public iterator_adaptor_base<iterator, NodeVectorImplT::iterator,
std::forward_iterator_tag, Node> {
friend class LazyCallGraph;
friend class LazyCallGraph::Node;
LazyCallGraph *G;
NodeVectorImplT::iterator E;
// Build the iterator for a specific position in a node list.
iterator(LazyCallGraph &G, NodeVectorImplT::iterator NI,
NodeVectorImplT::iterator E)
: iterator_adaptor_base(NI), G(&G), E(E) {
while (I != E && I->isNull())
++I;
}
public:
iterator() {}
using iterator_adaptor_base::operator++;
iterator &operator++() {
do {
++I;
} while (I != E && I->isNull());
return *this;
}
reference operator*() const {
if (I->is<Node *>())
return *I->get<Node *>();
Function *F = I->get<Function *>();
Node &ChildN = G->get(*F);
*I = &ChildN;
return ChildN;
}
};
/// \brief A node in the call graph.
///
/// This represents a single node. It's primary roles are to cache the list of
/// callees, de-duplicate and provide fast testing of whether a function is
/// a callee, and facilitate iteration of child nodes in the graph.
class Node {
friend class LazyCallGraph;
friend class LazyCallGraph::SCC;
LazyCallGraph *G;
Function &F;
// We provide for the DFS numbering and Tarjan walk lowlink numbers to be
// stored directly within the node.
int DFSNumber;
int LowLink;
mutable NodeVectorT Callees;
DenseMap<Function *, size_t> CalleeIndexMap;
/// \brief Basic constructor implements the scanning of F into Callees and
/// CalleeIndexMap.
Node(LazyCallGraph &G, Function &F);
/// \brief Internal helper to insert a callee.
void insertEdgeInternal(Function &Callee);
/// \brief Internal helper to insert a callee.
void insertEdgeInternal(Node &CalleeN);
/// \brief Internal helper to remove a callee from this node.
void removeEdgeInternal(Function &Callee);
public:
typedef LazyCallGraph::iterator iterator;
Function &getFunction() const {
return F;
};
iterator begin() const {
return iterator(*G, Callees.begin(), Callees.end());
}
iterator end() const { return iterator(*G, Callees.end(), Callees.end()); }
/// Equality is defined as address equality.
bool operator==(const Node &N) const { return this == &N; }
bool operator!=(const Node &N) const { return !operator==(N); }
};
/// \brief An SCC of the call graph.
///
/// This represents a Strongly Connected Component of the call graph as
/// a collection of call graph nodes. While the order of nodes in the SCC is
/// stable, it is not any particular order.
class SCC {
friend class LazyCallGraph;
friend class LazyCallGraph::Node;
LazyCallGraph *G;
SmallPtrSet<SCC *, 1> ParentSCCs;
SmallVector<Node *, 1> Nodes;
SCC(LazyCallGraph &G) : G(&G) {}
void insert(Node &N);
void
internalDFS(SmallVectorImpl<std::pair<Node *, Node::iterator>> &DFSStack,
SmallVectorImpl<Node *> &PendingSCCStack, Node *N,
SmallVectorImpl<SCC *> &ResultSCCs);
public:
typedef SmallVectorImpl<Node *>::const_iterator iterator;
typedef pointee_iterator<SmallPtrSet<SCC *, 1>::const_iterator> parent_iterator;
iterator begin() const { return Nodes.begin(); }
iterator end() const { return Nodes.end(); }
parent_iterator parent_begin() const { return ParentSCCs.begin(); }
parent_iterator parent_end() const { return ParentSCCs.end(); }
iterator_range<parent_iterator> parents() const {
return iterator_range<parent_iterator>(parent_begin(), parent_end());
}
/// \brief Test if this SCC is a parent of \a C.
bool isParentOf(const SCC &C) const { return C.isChildOf(*this); }
/// \brief Test if this SCC is an ancestor of \a C.
bool isAncestorOf(const SCC &C) const { return C.isDescendantOf(*this); }
/// \brief Test if this SCC is a child of \a C.
bool isChildOf(const SCC &C) const {
return ParentSCCs.count(const_cast<SCC *>(&C));
}
/// \brief Test if this SCC is a descendant of \a C.
bool isDescendantOf(const SCC &C) const;
/// \brief Short name useful for debugging or logging.
///
/// We use the name of the first function in the SCC to name the SCC for
/// the purposes of debugging and logging.
StringRef getName() const { return (*begin())->getFunction().getName(); }
///@{
/// \name Mutation API
///
/// These methods provide the core API for updating the call graph in the
/// presence of a (potentially still in-flight) DFS-found SCCs.
///
/// Note that these methods sometimes have complex runtimes, so be careful
/// how you call them.
/// \brief Insert an edge from one node in this SCC to another in this SCC.
///
/// By the definition of an SCC, this does not change the nature or make-up
/// of any SCCs.
void insertIntraSCCEdge(Node &CallerN, Node &CalleeN);
/// \brief Insert an edge whose tail is in this SCC and head is in some
/// child SCC.
///
/// There must be an existing path from the caller to the callee. This
/// operation is inexpensive and does not change the set of SCCs in the
/// graph.
void insertOutgoingEdge(Node &CallerN, Node &CalleeN);
/// \brief Insert an edge whose tail is in a descendant SCC and head is in
/// this SCC.
///
/// There must be an existing path from the callee to the caller in this
/// case. NB! This is has the potential to be a very expensive function. It
/// inherently forms a cycle in the prior SCC DAG and we have to merge SCCs
/// to resolve that cycle. But finding all of the SCCs which participate in
/// the cycle can in the worst case require traversing every SCC in the
/// graph. Every attempt is made to avoid that, but passes must still
/// exercise caution calling this routine repeatedly.
///
/// FIXME: We could possibly optimize this quite a bit for cases where the
/// caller and callee are very nearby in the graph. See comments in the
/// implementation for details, but that use case might impact users.
SmallVector<SCC *, 1> insertIncomingEdge(Node &CallerN, Node &CalleeN);
/// \brief Remove an edge whose source is in this SCC and target is *not*.
///
/// This removes an inter-SCC edge. All inter-SCC edges originating from
/// this SCC have been fully explored by any in-flight DFS SCC formation,
/// so this is always safe to call once you have the source SCC.
///
/// This operation does not change the set of SCCs or the members of the
/// SCCs and so is very inexpensive. It may change the connectivity graph
/// of the SCCs though, so be careful calling this while iterating over
/// them.
void removeInterSCCEdge(Node &CallerN, Node &CalleeN);
/// \brief Remove an edge which is entirely within this SCC.
///
/// Both the \a Caller and the \a Callee must be within this SCC. Removing
/// such an edge make break cycles that form this SCC and thus this
/// operation may change the SCC graph significantly. In particular, this
/// operation will re-form new SCCs based on the remaining connectivity of
/// the graph. The following invariants are guaranteed to hold after
/// calling this method:
///
/// 1) This SCC is still an SCC in the graph.
/// 2) This SCC will be the parent of any new SCCs. Thus, this SCC is
/// preserved as the root of any new SCC directed graph formed.
/// 3) No SCC other than this SCC has its member set changed (this is
/// inherent in the definition of removing such an edge).
/// 4) All of the parent links of the SCC graph will be updated to reflect
/// the new SCC structure.
/// 5) All SCCs formed out of this SCC, excluding this SCC, will be
/// returned in a vector.
/// 6) The order of the SCCs in the vector will be a valid postorder
/// traversal of the new SCCs.
///
/// These invariants are very important to ensure that we can build
/// optimization pipeliens on top of the CGSCC pass manager which
/// intelligently update the SCC graph without invalidating other parts of
/// the SCC graph.
///
/// The runtime complexity of this method is, in the worst case, O(V+E)
/// where V is the number of nodes in this SCC and E is the number of edges
/// leaving the nodes in this SCC. Note that E includes both edges within
/// this SCC and edges from this SCC to child SCCs. Some effort has been
/// made to minimize the overhead of common cases such as self-edges and
/// edge removals which result in a spanning tree with no more cycles.
SmallVector<SCC *, 1> removeIntraSCCEdge(Node &CallerN, Node &CalleeN);
///@}
};
/// \brief A post-order depth-first SCC iterator over the call graph.
///
/// This iterator triggers the Tarjan DFS-based formation of the SCC DAG for
/// the call graph, walking it lazily in depth-first post-order. That is, it
/// always visits SCCs for a callee prior to visiting the SCC for a caller
/// (when they are in different SCCs).
class postorder_scc_iterator
: public iterator_facade_base<postorder_scc_iterator,
std::forward_iterator_tag, SCC> {
friend class LazyCallGraph;
friend class LazyCallGraph::Node;
/// \brief Nonce type to select the constructor for the end iterator.
struct IsAtEndT {};
LazyCallGraph *G;
SCC *C;
// Build the begin iterator for a node.
postorder_scc_iterator(LazyCallGraph &G) : G(&G) {
C = G.getNextSCCInPostOrder();
}
// Build the end iterator for a node. This is selected purely by overload.
postorder_scc_iterator(LazyCallGraph &G, IsAtEndT /*Nonce*/)
: G(&G), C(nullptr) {}
public:
bool operator==(const postorder_scc_iterator &Arg) const {
return G == Arg.G && C == Arg.C;
}
reference operator*() const { return *C; }
using iterator_facade_base::operator++;
postorder_scc_iterator &operator++() {
C = G->getNextSCCInPostOrder();
return *this;
}
};
/// \brief Construct a graph for the given module.
///
/// This sets up the graph and computes all of the entry points of the graph.
/// No function definitions are scanned until their nodes in the graph are
/// requested during traversal.
LazyCallGraph(Module &M);
LazyCallGraph(LazyCallGraph &&G);
LazyCallGraph &operator=(LazyCallGraph &&RHS);
iterator begin() {
return iterator(*this, EntryNodes.begin(), EntryNodes.end());
}
iterator end() { return iterator(*this, EntryNodes.end(), EntryNodes.end()); }
postorder_scc_iterator postorder_scc_begin() {
return postorder_scc_iterator(*this);
}
postorder_scc_iterator postorder_scc_end() {
return postorder_scc_iterator(*this, postorder_scc_iterator::IsAtEndT());
}
iterator_range<postorder_scc_iterator> postorder_sccs() {
return iterator_range<postorder_scc_iterator>(postorder_scc_begin(),
postorder_scc_end());
}
/// \brief Lookup a function in the graph which has already been scanned and
/// added.
Node *lookup(const Function &F) const { return NodeMap.lookup(&F); }
/// \brief Lookup a function's SCC in the graph.
///
/// \returns null if the function hasn't been assigned an SCC via the SCC
/// iterator walk.
SCC *lookupSCC(Node &N) const { return SCCMap.lookup(&N); }
/// \brief Get a graph node for a given function, scanning it to populate the
/// graph data as necessary.
Node &get(Function &F) {
Node *&N = NodeMap[&F];
if (N)
return *N;
return insertInto(F, N);
}
///@{
/// \name Pre-SCC Mutation API
///
/// These methods are only valid to call prior to forming any SCCs for this
/// call graph. They can be used to update the core node-graph during
/// a node-based inorder traversal that precedes any SCC-based traversal.
///
/// Once you begin manipulating a call graph's SCCs, you must perform all
/// mutation of the graph via the SCC methods.
/// \brief Update the call graph after inserting a new edge.
void insertEdge(Node &Caller, Function &Callee);
/// \brief Update the call graph after inserting a new edge.
void insertEdge(Function &Caller, Function &Callee) {
return insertEdge(get(Caller), Callee);
}
/// \brief Update the call graph after deleting an edge.
void removeEdge(Node &Caller, Function &Callee);
/// \brief Update the call graph after deleting an edge.
void removeEdge(Function &Caller, Function &Callee) {
return removeEdge(get(Caller), Callee);
}
///@}
private:
/// \brief Allocator that holds all the call graph nodes.
SpecificBumpPtrAllocator<Node> BPA;
/// \brief Maps function->node for fast lookup.
DenseMap<const Function *, Node *> NodeMap;
/// \brief The entry nodes to the graph.
///
/// These nodes are reachable through "external" means. Put another way, they
/// escape at the module scope.
NodeVectorT EntryNodes;
/// \brief Map of the entry nodes in the graph to their indices in
/// \c EntryNodes.
DenseMap<Function *, size_t> EntryIndexMap;
/// \brief Allocator that holds all the call graph SCCs.
SpecificBumpPtrAllocator<SCC> SCCBPA;
/// \brief Maps Function -> SCC for fast lookup.
DenseMap<Node *, SCC *> SCCMap;
/// \brief The leaf SCCs of the graph.
///
/// These are all of the SCCs which have no children.
SmallVector<SCC *, 4> LeafSCCs;
/// \brief Stack of nodes in the DFS walk.
SmallVector<std::pair<Node *, iterator>, 4> DFSStack;
/// \brief Set of entry nodes not-yet-processed into SCCs.
SmallVector<Function *, 4> SCCEntryNodes;
/// \brief Stack of nodes the DFS has walked but not yet put into a SCC.
SmallVector<Node *, 4> PendingSCCStack;
/// \brief Counter for the next DFS number to assign.
int NextDFSNumber;
/// \brief Helper to insert a new function, with an already looked-up entry in
/// the NodeMap.
Node &insertInto(Function &F, Node *&MappedN);
/// \brief Helper to update pointers back to the graph object during moves.
void updateGraphPtrs();
/// \brief Helper to form a new SCC out of the top of a DFSStack-like
/// structure.
SCC *formSCC(Node *RootN, SmallVectorImpl<Node *> &NodeStack);
/// \brief Retrieve the next node in the post-order SCC walk of the call graph.
SCC *getNextSCCInPostOrder();
};
// Provide GraphTraits specializations for call graphs.
template <> struct GraphTraits<LazyCallGraph::Node *> {
typedef LazyCallGraph::Node NodeType;
typedef LazyCallGraph::iterator ChildIteratorType;
static NodeType *getEntryNode(NodeType *N) { return N; }
static ChildIteratorType child_begin(NodeType *N) { return N->begin(); }
static ChildIteratorType child_end(NodeType *N) { return N->end(); }
};
template <> struct GraphTraits<LazyCallGraph *> {
typedef LazyCallGraph::Node NodeType;
typedef LazyCallGraph::iterator ChildIteratorType;
static NodeType *getEntryNode(NodeType *N) { return N; }
static ChildIteratorType child_begin(NodeType *N) { return N->begin(); }
static ChildIteratorType child_end(NodeType *N) { return N->end(); }
};
/// \brief An analysis pass which computes the call graph for a module.
class LazyCallGraphAnalysis {
public:
/// \brief Inform generic clients of the result type.
typedef LazyCallGraph Result;
static void *ID() { return (void *)&PassID; }
static StringRef name() { return "Lazy CallGraph Analysis"; }
/// \brief Compute the \c LazyCallGraph for the module \c M.
///
/// This just builds the set of entry points to the call graph. The rest is
/// built lazily as it is walked.
LazyCallGraph run(Module &M) { return LazyCallGraph(M); }
private:
static char PassID;
};
/// \brief A pass which prints the call graph to a \c raw_ostream.
///
/// This is primarily useful for testing the analysis.
class LazyCallGraphPrinterPass {
raw_ostream &OS;
public:
explicit LazyCallGraphPrinterPass(raw_ostream &OS);
PreservedAnalyses run(Module &M, ModuleAnalysisManager *AM);
static StringRef name() { return "LazyCallGraphPrinterPass"; }
};
}
#endif