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llvm-mirror/lib/CodeGen/MachineOutliner.cpp
Jessica Paquette defcea1d16 [MachineOutliner] Add useMachineOutliner target hook 
The MachineOutliner has a bunch of target hooks that will call llvm_unreachable
if the target doesn't implement them. Therefore, if you enable the outliner on
such a target, it'll just crash. It'd be much better if it'd just *not* run
the outliner at all in this case.

This commit adds a hook to TargetInstrInfo that returns false by default.
Targets that implement the hook make it return true. The outliner checks the
return value of this hook to decide whether or not to continue.

llvm-svn: 329220
2018-04-04 19:13:31 +00:00

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//===---- MachineOutliner.cpp - Outline instructions -----------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// Replaces repeated sequences of instructions with function calls.
///
/// This works by placing every instruction from every basic block in a
/// suffix tree, and repeatedly querying that tree for repeated sequences of
/// instructions. If a sequence of instructions appears often, then it ought
/// to be beneficial to pull out into a function.
///
/// The MachineOutliner communicates with a given target using hooks defined in
/// TargetInstrInfo.h. The target supplies the outliner with information on how
/// a specific sequence of instructions should be outlined. This information
/// is used to deduce the number of instructions necessary to
///
/// * Create an outlined function
/// * Call that outlined function
///
/// Targets must implement
/// * getOutliningCandidateInfo
/// * insertOutlinerEpilogue
/// * insertOutlinedCall
/// * insertOutlinerPrologue
/// * isFunctionSafeToOutlineFrom
///
/// in order to make use of the MachineOutliner.
///
/// This was originally presented at the 2016 LLVM Developers' Meeting in the
/// talk "Reducing Code Size Using Outlining". For a high-level overview of
/// how this pass works, the talk is available on YouTube at
///
/// https://www.youtube.com/watch?v=yorld-WSOeU
///
/// The slides for the talk are available at
///
/// http://www.llvm.org/devmtg/2016-11/Slides/Paquette-Outliner.pdf
///
/// The talk provides an overview of how the outliner finds candidates and
/// ultimately outlines them. It describes how the main data structure for this
/// pass, the suffix tree, is queried and purged for candidates. It also gives
/// a simplified suffix tree construction algorithm for suffix trees based off
/// of the algorithm actually used here, Ukkonen's algorithm.
///
/// For the original RFC for this pass, please see
///
/// http://lists.llvm.org/pipermail/llvm-dev/2016-August/104170.html
///
/// For more information on the suffix tree data structure, please see
/// https://www.cs.helsinki.fi/u/ukkonen/SuffixT1withFigs.pdf
///
//===----------------------------------------------------------------------===//
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/Twine.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Mangler.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <functional>
#include <map>
#include <sstream>
#include <tuple>
#include <vector>
#define DEBUG_TYPE "machine-outliner"
using namespace llvm;
using namespace ore;
STATISTIC(NumOutlined, "Number of candidates outlined");
STATISTIC(FunctionsCreated, "Number of functions created");
namespace {
/// \brief An individual sequence of instructions to be replaced with a call to
/// an outlined function.
struct Candidate {
private:
/// The start index of this \p Candidate in the instruction list.
unsigned StartIdx;
/// The number of instructions in this \p Candidate.
unsigned Len;
/// The MachineFunction containing this \p Candidate.
MachineFunction *MF = nullptr;
public:
/// Set to false if the candidate overlapped with another candidate.
bool InCandidateList = true;
/// \brief The index of this \p Candidate's \p OutlinedFunction in the list of
/// \p OutlinedFunctions.
unsigned FunctionIdx;
/// Contains all target-specific information for this \p Candidate.
TargetInstrInfo::MachineOutlinerInfo MInfo;
/// If there is a DISubprogram associated with the function that this
/// Candidate lives in, return it.
DISubprogram *getSubprogramOrNull() const {
assert(MF && "Candidate has no MF!");
if (DISubprogram *SP = MF->getFunction().getSubprogram())
return SP;
return nullptr;
}
/// Return the number of instructions in this Candidate.
unsigned getLength() const { return Len; }
/// Return the start index of this candidate.
unsigned getStartIdx() const { return StartIdx; }
// Return the end index of this candidate.
unsigned getEndIdx() const { return StartIdx + Len - 1; }
/// \brief The number of instructions that would be saved by outlining every
/// candidate of this type.
///
/// This is a fixed value which is not updated during the candidate pruning
/// process. It is only used for deciding which candidate to keep if two
/// candidates overlap. The true benefit is stored in the OutlinedFunction
/// for some given candidate.
unsigned Benefit = 0;
Candidate(unsigned StartIdx, unsigned Len, unsigned FunctionIdx,
MachineFunction *MF)
: StartIdx(StartIdx), Len(Len), MF(MF), FunctionIdx(FunctionIdx) {}
Candidate() {}
/// \brief Used to ensure that \p Candidates are outlined in an order that
/// preserves the start and end indices of other \p Candidates.
bool operator<(const Candidate &RHS) const {
return getStartIdx() > RHS.getStartIdx();
}
};
/// \brief The information necessary to create an outlined function for some
/// class of candidate.
struct OutlinedFunction {
private:
/// The number of candidates for this \p OutlinedFunction.
unsigned OccurrenceCount = 0;
public:
std::vector<std::shared_ptr<Candidate>> Candidates;
/// The actual outlined function created.
/// This is initialized after we go through and create the actual function.
MachineFunction *MF = nullptr;
/// A number assigned to this function which appears at the end of its name.
unsigned Name;
/// \brief The sequence of integers corresponding to the instructions in this
/// function.
std::vector<unsigned> Sequence;
/// Contains all target-specific information for this \p OutlinedFunction.
TargetInstrInfo::MachineOutlinerInfo MInfo;
/// If there is a DISubprogram for any Candidate for this outlined function,
/// then return it. Otherwise, return nullptr.
DISubprogram *getSubprogramOrNull() const {
for (const auto &C : Candidates)
if (DISubprogram *SP = C->getSubprogramOrNull())
return SP;
return nullptr;
}
/// Return the number of candidates for this \p OutlinedFunction.
unsigned getOccurrenceCount() { return OccurrenceCount; }
/// Decrement the occurrence count of this OutlinedFunction and return the
/// new count.
unsigned decrement() {
assert(OccurrenceCount > 0 && "Can't decrement an empty function!");
OccurrenceCount--;
return getOccurrenceCount();
}
/// \brief Return the number of instructions it would take to outline this
/// function.
unsigned getOutliningCost() {
return (OccurrenceCount * MInfo.CallOverhead) + Sequence.size() +
MInfo.FrameOverhead;
}
/// \brief Return the number of instructions that would be saved by outlining
/// this function.
unsigned getBenefit() {
unsigned NotOutlinedCost = OccurrenceCount * Sequence.size();
unsigned OutlinedCost = getOutliningCost();
return (NotOutlinedCost < OutlinedCost) ? 0
: NotOutlinedCost - OutlinedCost;
}
OutlinedFunction(unsigned Name, unsigned OccurrenceCount,
const std::vector<unsigned> &Sequence,
TargetInstrInfo::MachineOutlinerInfo &MInfo)
: OccurrenceCount(OccurrenceCount), Name(Name), Sequence(Sequence),
MInfo(MInfo) {}
};
/// Represents an undefined index in the suffix tree.
const unsigned EmptyIdx = -1;
/// A node in a suffix tree which represents a substring or suffix.
///
/// Each node has either no children or at least two children, with the root
/// being a exception in the empty tree.
///
/// Children are represented as a map between unsigned integers and nodes. If
/// a node N has a child M on unsigned integer k, then the mapping represented
/// by N is a proper prefix of the mapping represented by M. Note that this,
/// although similar to a trie is somewhat different: each node stores a full
/// substring of the full mapping rather than a single character state.
///
/// Each internal node contains a pointer to the internal node representing
/// the same string, but with the first character chopped off. This is stored
/// in \p Link. Each leaf node stores the start index of its respective
/// suffix in \p SuffixIdx.
struct SuffixTreeNode {
/// The children of this node.
///
/// A child existing on an unsigned integer implies that from the mapping
/// represented by the current node, there is a way to reach another
/// mapping by tacking that character on the end of the current string.
DenseMap<unsigned, SuffixTreeNode *> Children;
/// A flag set to false if the node has been pruned from the tree.
bool IsInTree = true;
/// The start index of this node's substring in the main string.
unsigned StartIdx = EmptyIdx;
/// The end index of this node's substring in the main string.
///
/// Every leaf node must have its \p EndIdx incremented at the end of every
/// step in the construction algorithm. To avoid having to update O(N)
/// nodes individually at the end of every step, the end index is stored
/// as a pointer.
unsigned *EndIdx = nullptr;
/// For leaves, the start index of the suffix represented by this node.
///
/// For all other nodes, this is ignored.
unsigned SuffixIdx = EmptyIdx;
/// \brief For internal nodes, a pointer to the internal node representing
/// the same sequence with the first character chopped off.
///
/// This acts as a shortcut in Ukkonen's algorithm. One of the things that
/// Ukkonen's algorithm does to achieve linear-time construction is
/// keep track of which node the next insert should be at. This makes each
/// insert O(1), and there are a total of O(N) inserts. The suffix link
/// helps with inserting children of internal nodes.
///
/// Say we add a child to an internal node with associated mapping S. The
/// next insertion must be at the node representing S - its first character.
/// This is given by the way that we iteratively build the tree in Ukkonen's
/// algorithm. The main idea is to look at the suffixes of each prefix in the
/// string, starting with the longest suffix of the prefix, and ending with
/// the shortest. Therefore, if we keep pointers between such nodes, we can
/// move to the next insertion point in O(1) time. If we don't, then we'd
/// have to query from the root, which takes O(N) time. This would make the
/// construction algorithm O(N^2) rather than O(N).
SuffixTreeNode *Link = nullptr;
/// The parent of this node. Every node except for the root has a parent.
SuffixTreeNode *Parent = nullptr;
/// The number of times this node's string appears in the tree.
///
/// This is equal to the number of leaf children of the string. It represents
/// the number of suffixes that the node's string is a prefix of.
unsigned OccurrenceCount = 0;
/// The length of the string formed by concatenating the edge labels from the
/// root to this node.
unsigned ConcatLen = 0;
/// Returns true if this node is a leaf.
bool isLeaf() const { return SuffixIdx != EmptyIdx; }
/// Returns true if this node is the root of its owning \p SuffixTree.
bool isRoot() const { return StartIdx == EmptyIdx; }
/// Return the number of elements in the substring associated with this node.
size_t size() const {
// Is it the root? If so, it's the empty string so return 0.
if (isRoot())
return 0;
assert(*EndIdx != EmptyIdx && "EndIdx is undefined!");
// Size = the number of elements in the string.
// For example, [0 1 2 3] has length 4, not 3. 3-0 = 3, so we have 3-0+1.
return *EndIdx - StartIdx + 1;
}
SuffixTreeNode(unsigned StartIdx, unsigned *EndIdx, SuffixTreeNode *Link,
SuffixTreeNode *Parent)
: StartIdx(StartIdx), EndIdx(EndIdx), Link(Link), Parent(Parent) {}
SuffixTreeNode() {}
};
/// A data structure for fast substring queries.
///
/// Suffix trees represent the suffixes of their input strings in their leaves.
/// A suffix tree is a type of compressed trie structure where each node
/// represents an entire substring rather than a single character. Each leaf
/// of the tree is a suffix.
///
/// A suffix tree can be seen as a type of state machine where each state is a
/// substring of the full string. The tree is structured so that, for a string
/// of length N, there are exactly N leaves in the tree. This structure allows
/// us to quickly find repeated substrings of the input string.
///
/// In this implementation, a "string" is a vector of unsigned integers.
/// These integers may result from hashing some data type. A suffix tree can
/// contain 1 or many strings, which can then be queried as one large string.
///
/// The suffix tree is implemented using Ukkonen's algorithm for linear-time
/// suffix tree construction. Ukkonen's algorithm is explained in more detail
/// in the paper by Esko Ukkonen "On-line construction of suffix trees. The
/// paper is available at
///
/// https://www.cs.helsinki.fi/u/ukkonen/SuffixT1withFigs.pdf
class SuffixTree {
public:
/// Stores each leaf node in the tree.
///
/// This is used for finding outlining candidates.
std::vector<SuffixTreeNode *> LeafVector;
/// Each element is an integer representing an instruction in the module.
ArrayRef<unsigned> Str;
private:
/// Maintains each node in the tree.
SpecificBumpPtrAllocator<SuffixTreeNode> NodeAllocator;
/// The root of the suffix tree.
///
/// The root represents the empty string. It is maintained by the
/// \p NodeAllocator like every other node in the tree.
SuffixTreeNode *Root = nullptr;
/// Maintains the end indices of the internal nodes in the tree.
///
/// Each internal node is guaranteed to never have its end index change
/// during the construction algorithm; however, leaves must be updated at
/// every step. Therefore, we need to store leaf end indices by reference
/// to avoid updating O(N) leaves at every step of construction. Thus,
/// every internal node must be allocated its own end index.
BumpPtrAllocator InternalEndIdxAllocator;
/// The end index of each leaf in the tree.
unsigned LeafEndIdx = -1;
/// \brief Helper struct which keeps track of the next insertion point in
/// Ukkonen's algorithm.
struct ActiveState {
/// The next node to insert at.
SuffixTreeNode *Node;
/// The index of the first character in the substring currently being added.
unsigned Idx = EmptyIdx;
/// The length of the substring we have to add at the current step.
unsigned Len = 0;
};
/// \brief The point the next insertion will take place at in the
/// construction algorithm.
ActiveState Active;
/// Allocate a leaf node and add it to the tree.
///
/// \param Parent The parent of this node.
/// \param StartIdx The start index of this node's associated string.
/// \param Edge The label on the edge leaving \p Parent to this node.
///
/// \returns A pointer to the allocated leaf node.
SuffixTreeNode *insertLeaf(SuffixTreeNode &Parent, unsigned StartIdx,
unsigned Edge) {
assert(StartIdx <= LeafEndIdx && "String can't start after it ends!");
SuffixTreeNode *N = new (NodeAllocator.Allocate())
SuffixTreeNode(StartIdx, &LeafEndIdx, nullptr, &Parent);
Parent.Children[Edge] = N;
return N;
}
/// Allocate an internal node and add it to the tree.
///
/// \param Parent The parent of this node. Only null when allocating the root.
/// \param StartIdx The start index of this node's associated string.
/// \param EndIdx The end index of this node's associated string.
/// \param Edge The label on the edge leaving \p Parent to this node.
///
/// \returns A pointer to the allocated internal node.
SuffixTreeNode *insertInternalNode(SuffixTreeNode *Parent, unsigned StartIdx,
unsigned EndIdx, unsigned Edge) {
assert(StartIdx <= EndIdx && "String can't start after it ends!");
assert(!(!Parent && StartIdx != EmptyIdx) &&
"Non-root internal nodes must have parents!");
unsigned *E = new (InternalEndIdxAllocator) unsigned(EndIdx);
SuffixTreeNode *N = new (NodeAllocator.Allocate())
SuffixTreeNode(StartIdx, E, Root, Parent);
if (Parent)
Parent->Children[Edge] = N;
return N;
}
/// \brief Set the suffix indices of the leaves to the start indices of their
/// respective suffixes. Also stores each leaf in \p LeafVector at its
/// respective suffix index.
///
/// \param[in] CurrNode The node currently being visited.
/// \param CurrIdx The current index of the string being visited.
void setSuffixIndices(SuffixTreeNode &CurrNode, unsigned CurrIdx) {
bool IsLeaf = CurrNode.Children.size() == 0 && !CurrNode.isRoot();
// Store the length of the concatenation of all strings from the root to
// this node.
if (!CurrNode.isRoot()) {
if (CurrNode.ConcatLen == 0)
CurrNode.ConcatLen = CurrNode.size();
if (CurrNode.Parent)
CurrNode.ConcatLen += CurrNode.Parent->ConcatLen;
}
// Traverse the tree depth-first.
for (auto &ChildPair : CurrNode.Children) {
assert(ChildPair.second && "Node had a null child!");
setSuffixIndices(*ChildPair.second, CurrIdx + ChildPair.second->size());
}
// Is this node a leaf?
if (IsLeaf) {
// If yes, give it a suffix index and bump its parent's occurrence count.
CurrNode.SuffixIdx = Str.size() - CurrIdx;
assert(CurrNode.Parent && "CurrNode had no parent!");
CurrNode.Parent->OccurrenceCount++;
// Store the leaf in the leaf vector for pruning later.
LeafVector[CurrNode.SuffixIdx] = &CurrNode;
}
}
/// \brief Construct the suffix tree for the prefix of the input ending at
/// \p EndIdx.
///
/// Used to construct the full suffix tree iteratively. At the end of each
/// step, the constructed suffix tree is either a valid suffix tree, or a
/// suffix tree with implicit suffixes. At the end of the final step, the
/// suffix tree is a valid tree.
///
/// \param EndIdx The end index of the current prefix in the main string.
/// \param SuffixesToAdd The number of suffixes that must be added
/// to complete the suffix tree at the current phase.
///
/// \returns The number of suffixes that have not been added at the end of
/// this step.
unsigned extend(unsigned EndIdx, unsigned SuffixesToAdd) {
SuffixTreeNode *NeedsLink = nullptr;
while (SuffixesToAdd > 0) {
// Are we waiting to add anything other than just the last character?
if (Active.Len == 0) {
// If not, then say the active index is the end index.
Active.Idx = EndIdx;
}
assert(Active.Idx <= EndIdx && "Start index can't be after end index!");
// The first character in the current substring we're looking at.
unsigned FirstChar = Str[Active.Idx];
// Have we inserted anything starting with FirstChar at the current node?
if (Active.Node->Children.count(FirstChar) == 0) {
// If not, then we can just insert a leaf and move too the next step.
insertLeaf(*Active.Node, EndIdx, FirstChar);
// The active node is an internal node, and we visited it, so it must
// need a link if it doesn't have one.
if (NeedsLink) {
NeedsLink->Link = Active.Node;
NeedsLink = nullptr;
}
} else {
// There's a match with FirstChar, so look for the point in the tree to
// insert a new node.
SuffixTreeNode *NextNode = Active.Node->Children[FirstChar];
unsigned SubstringLen = NextNode->size();
// Is the current suffix we're trying to insert longer than the size of
// the child we want to move to?
if (Active.Len >= SubstringLen) {
// If yes, then consume the characters we've seen and move to the next
// node.
Active.Idx += SubstringLen;
Active.Len -= SubstringLen;
Active.Node = NextNode;
continue;
}
// Otherwise, the suffix we're trying to insert must be contained in the
// next node we want to move to.
unsigned LastChar = Str[EndIdx];
// Is the string we're trying to insert a substring of the next node?
if (Str[NextNode->StartIdx + Active.Len] == LastChar) {
// If yes, then we're done for this step. Remember our insertion point
// and move to the next end index. At this point, we have an implicit
// suffix tree.
if (NeedsLink && !Active.Node->isRoot()) {
NeedsLink->Link = Active.Node;
NeedsLink = nullptr;
}
Active.Len++;
break;
}
// The string we're trying to insert isn't a substring of the next node,
// but matches up to a point. Split the node.
//
// For example, say we ended our search at a node n and we're trying to
// insert ABD. Then we'll create a new node s for AB, reduce n to just
// representing C, and insert a new leaf node l to represent d. This
// allows us to ensure that if n was a leaf, it remains a leaf.
//
// | ABC ---split---> | AB
// n s
// C / \ D
// n l
// The node s from the diagram
SuffixTreeNode *SplitNode =
insertInternalNode(Active.Node, NextNode->StartIdx,
NextNode->StartIdx + Active.Len - 1, FirstChar);
// Insert the new node representing the new substring into the tree as
// a child of the split node. This is the node l from the diagram.
insertLeaf(*SplitNode, EndIdx, LastChar);
// Make the old node a child of the split node and update its start
// index. This is the node n from the diagram.
NextNode->StartIdx += Active.Len;
NextNode->Parent = SplitNode;
SplitNode->Children[Str[NextNode->StartIdx]] = NextNode;
// SplitNode is an internal node, update the suffix link.
if (NeedsLink)
NeedsLink->Link = SplitNode;
NeedsLink = SplitNode;
}
// We've added something new to the tree, so there's one less suffix to
// add.
SuffixesToAdd--;
if (Active.Node->isRoot()) {
if (Active.Len > 0) {
Active.Len--;
Active.Idx = EndIdx - SuffixesToAdd + 1;
}
} else {
// Start the next phase at the next smallest suffix.
Active.Node = Active.Node->Link;
}
}
return SuffixesToAdd;
}
public:
/// Construct a suffix tree from a sequence of unsigned integers.
///
/// \param Str The string to construct the suffix tree for.
SuffixTree(const std::vector<unsigned> &Str) : Str(Str) {
Root = insertInternalNode(nullptr, EmptyIdx, EmptyIdx, 0);
Root->IsInTree = true;
Active.Node = Root;
LeafVector = std::vector<SuffixTreeNode *>(Str.size());
// Keep track of the number of suffixes we have to add of the current
// prefix.
unsigned SuffixesToAdd = 0;
Active.Node = Root;
// Construct the suffix tree iteratively on each prefix of the string.
// PfxEndIdx is the end index of the current prefix.
// End is one past the last element in the string.
for (unsigned PfxEndIdx = 0, End = Str.size(); PfxEndIdx < End;
PfxEndIdx++) {
SuffixesToAdd++;
LeafEndIdx = PfxEndIdx; // Extend each of the leaves.
SuffixesToAdd = extend(PfxEndIdx, SuffixesToAdd);
}
// Set the suffix indices of each leaf.
assert(Root && "Root node can't be nullptr!");
setSuffixIndices(*Root, 0);
}
};
/// \brief Maps \p MachineInstrs to unsigned integers and stores the mappings.
struct InstructionMapper {
/// \brief The next available integer to assign to a \p MachineInstr that
/// cannot be outlined.
///
/// Set to -3 for compatability with \p DenseMapInfo<unsigned>.
unsigned IllegalInstrNumber = -3;
/// \brief The next available integer to assign to a \p MachineInstr that can
/// be outlined.
unsigned LegalInstrNumber = 0;
/// Correspondence from \p MachineInstrs to unsigned integers.
DenseMap<MachineInstr *, unsigned, MachineInstrExpressionTrait>
InstructionIntegerMap;
/// Corresponcence from unsigned integers to \p MachineInstrs.
/// Inverse of \p InstructionIntegerMap.
DenseMap<unsigned, MachineInstr *> IntegerInstructionMap;
/// The vector of unsigned integers that the module is mapped to.
std::vector<unsigned> UnsignedVec;
/// \brief Stores the location of the instruction associated with the integer
/// at index i in \p UnsignedVec for each index i.
std::vector<MachineBasicBlock::iterator> InstrList;
/// \brief Maps \p *It to a legal integer.
///
/// Updates \p InstrList, \p UnsignedVec, \p InstructionIntegerMap,
/// \p IntegerInstructionMap, and \p LegalInstrNumber.
///
/// \returns The integer that \p *It was mapped to.
unsigned mapToLegalUnsigned(MachineBasicBlock::iterator &It) {
// Get the integer for this instruction or give it the current
// LegalInstrNumber.
InstrList.push_back(It);
MachineInstr &MI = *It;
bool WasInserted;
DenseMap<MachineInstr *, unsigned, MachineInstrExpressionTrait>::iterator
ResultIt;
std::tie(ResultIt, WasInserted) =
InstructionIntegerMap.insert(std::make_pair(&MI, LegalInstrNumber));
unsigned MINumber = ResultIt->second;
// There was an insertion.
if (WasInserted) {
LegalInstrNumber++;
IntegerInstructionMap.insert(std::make_pair(MINumber, &MI));
}
UnsignedVec.push_back(MINumber);
// Make sure we don't overflow or use any integers reserved by the DenseMap.
if (LegalInstrNumber >= IllegalInstrNumber)
report_fatal_error("Instruction mapping overflow!");
assert(LegalInstrNumber != DenseMapInfo<unsigned>::getEmptyKey() &&
"Tried to assign DenseMap tombstone or empty key to instruction.");
assert(LegalInstrNumber != DenseMapInfo<unsigned>::getTombstoneKey() &&
"Tried to assign DenseMap tombstone or empty key to instruction.");
return MINumber;
}
/// Maps \p *It to an illegal integer.
///
/// Updates \p InstrList, \p UnsignedVec, and \p IllegalInstrNumber.
///
/// \returns The integer that \p *It was mapped to.
unsigned mapToIllegalUnsigned(MachineBasicBlock::iterator &It) {
unsigned MINumber = IllegalInstrNumber;
InstrList.push_back(It);
UnsignedVec.push_back(IllegalInstrNumber);
IllegalInstrNumber--;
assert(LegalInstrNumber < IllegalInstrNumber &&
"Instruction mapping overflow!");
assert(IllegalInstrNumber != DenseMapInfo<unsigned>::getEmptyKey() &&
"IllegalInstrNumber cannot be DenseMap tombstone or empty key!");
assert(IllegalInstrNumber != DenseMapInfo<unsigned>::getTombstoneKey() &&
"IllegalInstrNumber cannot be DenseMap tombstone or empty key!");
return MINumber;
}
/// \brief Transforms a \p MachineBasicBlock into a \p vector of \p unsigneds
/// and appends it to \p UnsignedVec and \p InstrList.
///
/// Two instructions are assigned the same integer if they are identical.
/// If an instruction is deemed unsafe to outline, then it will be assigned an
/// unique integer. The resulting mapping is placed into a suffix tree and
/// queried for candidates.
///
/// \param MBB The \p MachineBasicBlock to be translated into integers.
/// \param TRI \p TargetRegisterInfo for the module.
/// \param TII \p TargetInstrInfo for the module.
void convertToUnsignedVec(MachineBasicBlock &MBB,
const TargetRegisterInfo &TRI,
const TargetInstrInfo &TII) {
unsigned Flags = TII.getMachineOutlinerMBBFlags(MBB);
for (MachineBasicBlock::iterator It = MBB.begin(), Et = MBB.end(); It != Et;
It++) {
// Keep track of where this instruction is in the module.
switch (TII.getOutliningType(It, Flags)) {
case TargetInstrInfo::MachineOutlinerInstrType::Illegal:
mapToIllegalUnsigned(It);
break;
case TargetInstrInfo::MachineOutlinerInstrType::Legal:
mapToLegalUnsigned(It);
break;
case TargetInstrInfo::MachineOutlinerInstrType::Invisible:
break;
}
}
// After we're done every insertion, uniquely terminate this part of the
// "string". This makes sure we won't match across basic block or function
// boundaries since the "end" is encoded uniquely and thus appears in no
// repeated substring.
InstrList.push_back(MBB.end());
UnsignedVec.push_back(IllegalInstrNumber);
IllegalInstrNumber--;
}
InstructionMapper() {
// Make sure that the implementation of DenseMapInfo<unsigned> hasn't
// changed.
assert(DenseMapInfo<unsigned>::getEmptyKey() == (unsigned)-1 &&
"DenseMapInfo<unsigned>'s empty key isn't -1!");
assert(DenseMapInfo<unsigned>::getTombstoneKey() == (unsigned)-2 &&
"DenseMapInfo<unsigned>'s tombstone key isn't -2!");
}
};
/// \brief An interprocedural pass which finds repeated sequences of
/// instructions and replaces them with calls to functions.
///
/// Each instruction is mapped to an unsigned integer and placed in a string.
/// The resulting mapping is then placed in a \p SuffixTree. The \p SuffixTree
/// is then repeatedly queried for repeated sequences of instructions. Each
/// non-overlapping repeated sequence is then placed in its own
/// \p MachineFunction and each instance is then replaced with a call to that
/// function.
struct MachineOutliner : public ModulePass {
static char ID;
/// \brief Set to true if the outliner should consider functions with
/// linkonceodr linkage.
bool OutlineFromLinkOnceODRs = false;
// Collection of IR functions created by the outliner.
std::vector<Function *> CreatedIRFunctions;
StringRef getPassName() const override { return "Machine Outliner"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineModuleInfo>();
AU.addPreserved<MachineModuleInfo>();
AU.setPreservesAll();
ModulePass::getAnalysisUsage(AU);
}
MachineOutliner(bool OutlineFromLinkOnceODRs = false)
: ModulePass(ID), OutlineFromLinkOnceODRs(OutlineFromLinkOnceODRs) {
initializeMachineOutlinerPass(*PassRegistry::getPassRegistry());
}
/// Find all repeated substrings that satisfy the outlining cost model.
///
/// If a substring appears at least twice, then it must be represented by
/// an internal node which appears in at least two suffixes. Each suffix is
/// represented by a leaf node. To do this, we visit each internal node in
/// the tree, using the leaf children of each internal node. If an internal
/// node represents a beneficial substring, then we use each of its leaf
/// children to find the locations of its substring.
///
/// \param ST A suffix tree to query.
/// \param TII TargetInstrInfo for the target.
/// \param Mapper Contains outlining mapping information.
/// \param[out] CandidateList Filled with candidates representing each
/// beneficial substring.
/// \param[out] FunctionList Filled with a list of \p OutlinedFunctions each
/// type of candidate.
///
/// \returns The length of the longest candidate found.
unsigned
findCandidates(SuffixTree &ST, const TargetInstrInfo &TII,
InstructionMapper &Mapper,
std::vector<std::shared_ptr<Candidate>> &CandidateList,
std::vector<OutlinedFunction> &FunctionList);
/// \brief Replace the sequences of instructions represented by the
/// \p Candidates in \p CandidateList with calls to \p MachineFunctions
/// described in \p FunctionList.
///
/// \param M The module we are outlining from.
/// \param CandidateList A list of candidates to be outlined.
/// \param FunctionList A list of functions to be inserted into the module.
/// \param Mapper Contains the instruction mappings for the module.
bool outline(Module &M,
const ArrayRef<std::shared_ptr<Candidate>> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
InstructionMapper &Mapper);
/// Creates a function for \p OF and inserts it into the module.
MachineFunction *createOutlinedFunction(Module &M, const OutlinedFunction &OF,
InstructionMapper &Mapper);
/// Find potential outlining candidates and store them in \p CandidateList.
///
/// For each type of potential candidate, also build an \p OutlinedFunction
/// struct containing the information to build the function for that
/// candidate.
///
/// \param[out] CandidateList Filled with outlining candidates for the module.
/// \param[out] FunctionList Filled with functions corresponding to each type
/// of \p Candidate.
/// \param ST The suffix tree for the module.
/// \param TII TargetInstrInfo for the module.
///
/// \returns The length of the longest candidate found. 0 if there are none.
unsigned
buildCandidateList(std::vector<std::shared_ptr<Candidate>> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
SuffixTree &ST, InstructionMapper &Mapper,
const TargetInstrInfo &TII);
/// Helper function for pruneOverlaps.
/// Removes \p C from the candidate list, and updates its \p OutlinedFunction.
void prune(Candidate &C, std::vector<OutlinedFunction> &FunctionList);
/// \brief Remove any overlapping candidates that weren't handled by the
/// suffix tree's pruning method.
///
/// Pruning from the suffix tree doesn't necessarily remove all overlaps.
/// If a short candidate is chosen for outlining, then a longer candidate
/// which has that short candidate as a suffix is chosen, the tree's pruning
/// method will not find it. Thus, we need to prune before outlining as well.
///
/// \param[in,out] CandidateList A list of outlining candidates.
/// \param[in,out] FunctionList A list of functions to be outlined.
/// \param Mapper Contains instruction mapping info for outlining.
/// \param MaxCandidateLen The length of the longest candidate.
/// \param TII TargetInstrInfo for the module.
void pruneOverlaps(std::vector<std::shared_ptr<Candidate>> &CandidateList,
std::vector<OutlinedFunction> &FunctionList,
InstructionMapper &Mapper, unsigned MaxCandidateLen,
const TargetInstrInfo &TII);
/// Construct a suffix tree on the instructions in \p M and outline repeated
/// strings from that tree.
bool runOnModule(Module &M) override;
};
} // Anonymous namespace.
char MachineOutliner::ID = 0;
namespace llvm {
ModulePass *createMachineOutlinerPass(bool OutlineFromLinkOnceODRs) {
return new MachineOutliner(OutlineFromLinkOnceODRs);
}
} // namespace llvm
INITIALIZE_PASS(MachineOutliner, DEBUG_TYPE, "Machine Function Outliner", false,
false)
unsigned MachineOutliner::findCandidates(
SuffixTree &ST, const TargetInstrInfo &TII, InstructionMapper &Mapper,
std::vector<std::shared_ptr<Candidate>> &CandidateList,
std::vector<OutlinedFunction> &FunctionList) {
CandidateList.clear();
FunctionList.clear();
unsigned MaxLen = 0;
// FIXME: Visit internal nodes instead of leaves.
for (SuffixTreeNode *Leaf : ST.LeafVector) {
assert(Leaf && "Leaves in LeafVector cannot be null!");
if (!Leaf->IsInTree)
continue;
assert(Leaf->Parent && "All leaves must have parents!");
SuffixTreeNode &Parent = *(Leaf->Parent);
// If it doesn't appear enough, or we already outlined from it, skip it.
if (Parent.OccurrenceCount < 2 || Parent.isRoot() || !Parent.IsInTree)
continue;
// Figure out if this candidate is beneficial.
unsigned StringLen = Leaf->ConcatLen - (unsigned)Leaf->size();
// Too short to be beneficial; skip it.
// FIXME: This isn't necessarily true for, say, X86. If we factor in
// instruction lengths we need more information than this.
if (StringLen < 2)
continue;
// If this is a beneficial class of candidate, then every one is stored in
// this vector.
std::vector<Candidate> CandidatesForRepeatedSeq;
// Describes the start and end point of each candidate. This allows the
// target to infer some information about each occurrence of each repeated
// sequence.
// FIXME: CandidatesForRepeatedSeq and this should be combined.
std::vector<
std::pair<MachineBasicBlock::iterator, MachineBasicBlock::iterator>>
RepeatedSequenceLocs;
// Figure out the call overhead for each instance of the sequence.
for (auto &ChildPair : Parent.Children) {
SuffixTreeNode *M = ChildPair.second;
if (M && M->IsInTree && M->isLeaf()) {
// Never visit this leaf again.
M->IsInTree = false;
unsigned StartIdx = M->SuffixIdx;
unsigned EndIdx = StartIdx + StringLen - 1;
// Trick: Discard some candidates that would be incompatible with the
// ones we've already found for this sequence. This will save us some
// work in candidate selection.
//
// If two candidates overlap, then we can't outline them both. This
// happens when we have candidates that look like, say
//
// AA (where each "A" is an instruction).
//
// We might have some portion of the module that looks like this:
// AAAAAA (6 A's)
//
// In this case, there are 5 different copies of "AA" in this range, but
// at most 3 can be outlined. If only outlining 3 of these is going to
// be unbeneficial, then we ought to not bother.
//
// Note that two things DON'T overlap when they look like this:
// start1...end1 .... start2...end2
// That is, one must either
// * End before the other starts
// * Start after the other ends
if (std::all_of(CandidatesForRepeatedSeq.begin(),
CandidatesForRepeatedSeq.end(),
[&StartIdx, &EndIdx](const Candidate &C) {
return (EndIdx < C.getStartIdx() ||
StartIdx > C.getEndIdx());
})) {
// It doesn't overlap with anything, so we can outline it.
// Each sequence is over [StartIt, EndIt].
MachineBasicBlock::iterator StartIt = Mapper.InstrList[StartIdx];
MachineBasicBlock::iterator EndIt = Mapper.InstrList[EndIdx];
// Save the MachineFunction containing the Candidate.
MachineFunction *MF = StartIt->getParent()->getParent();
assert(MF && "Candidate doesn't have a MF?");
// Save the candidate and its location.
CandidatesForRepeatedSeq.emplace_back(StartIdx, StringLen,
FunctionList.size(), MF);
RepeatedSequenceLocs.emplace_back(std::make_pair(StartIt, EndIt));
}
}
}
// We've found something we might want to outline.
// Create an OutlinedFunction to store it and check if it'd be beneficial
// to outline.
TargetInstrInfo::MachineOutlinerInfo MInfo =
TII.getOutlininingCandidateInfo(RepeatedSequenceLocs);
std::vector<unsigned> Seq;
for (unsigned i = Leaf->SuffixIdx; i < Leaf->SuffixIdx + StringLen; i++)
Seq.push_back(ST.Str[i]);
OutlinedFunction OF(FunctionList.size(), CandidatesForRepeatedSeq.size(),
Seq, MInfo);
unsigned Benefit = OF.getBenefit();
// Is it better to outline this candidate than not?
if (Benefit < 1) {
// Outlining this candidate would take more instructions than not
// outlining.
// Emit a remark explaining why we didn't outline this candidate.
std::pair<MachineBasicBlock::iterator, MachineBasicBlock::iterator> C =
RepeatedSequenceLocs[0];
MachineOptimizationRemarkEmitter MORE(
*(C.first->getParent()->getParent()), nullptr);
MORE.emit([&]() {
MachineOptimizationRemarkMissed R(DEBUG_TYPE, "NotOutliningCheaper",
C.first->getDebugLoc(),
C.first->getParent());
R << "Did not outline " << NV("Length", StringLen) << " instructions"
<< " from " << NV("NumOccurrences", RepeatedSequenceLocs.size())
<< " locations."
<< " Instructions from outlining all occurrences ("
<< NV("OutliningCost", OF.getOutliningCost()) << ")"
<< " >= Unoutlined instruction count ("
<< NV("NotOutliningCost", StringLen * OF.getOccurrenceCount()) << ")"
<< " (Also found at: ";
// Tell the user the other places the candidate was found.
for (unsigned i = 1, e = RepeatedSequenceLocs.size(); i < e; i++) {
R << NV((Twine("OtherStartLoc") + Twine(i)).str(),
RepeatedSequenceLocs[i].first->getDebugLoc());
if (i != e - 1)
R << ", ";
}
R << ")";
return R;
});
// Move to the next candidate.
continue;
}
if (StringLen > MaxLen)
MaxLen = StringLen;
// At this point, the candidate class is seen as beneficial. Set their
// benefit values and save them in the candidate list.
std::vector<std::shared_ptr<Candidate>> CandidatesForFn;
for (Candidate &C : CandidatesForRepeatedSeq) {
C.Benefit = Benefit;
C.MInfo = MInfo;
std::shared_ptr<Candidate> Cptr = std::make_shared<Candidate>(C);
CandidateList.push_back(Cptr);
CandidatesForFn.push_back(Cptr);
}
FunctionList.push_back(OF);
FunctionList.back().Candidates = CandidatesForFn;
// Move to the next function.
Parent.IsInTree = false;
}
return MaxLen;
}
// Remove C from the candidate space, and update its OutlinedFunction.
void MachineOutliner::prune(Candidate &C,
std::vector<OutlinedFunction> &FunctionList) {
// Get the OutlinedFunction associated with this Candidate.
OutlinedFunction &F = FunctionList[C.FunctionIdx];
// Update C's associated function's occurrence count.
F.decrement();
// Remove C from the CandidateList.
C.InCandidateList = false;
DEBUG(dbgs() << "- Removed a Candidate \n";
dbgs() << "--- Num fns left for candidate: " << F.getOccurrenceCount()
<< "\n";
dbgs() << "--- Candidate's functions's benefit: " << F.getBenefit()
<< "\n";);
}
void MachineOutliner::pruneOverlaps(
std::vector<std::shared_ptr<Candidate>> &CandidateList,
std::vector<OutlinedFunction> &FunctionList, InstructionMapper &Mapper,
unsigned MaxCandidateLen, const TargetInstrInfo &TII) {
// Return true if this candidate became unbeneficial for outlining in a
// previous step.
auto ShouldSkipCandidate = [&FunctionList, this](Candidate &C) {
// Check if the candidate was removed in a previous step.
if (!C.InCandidateList)
return true;
// C must be alive. Check if we should remove it.
if (FunctionList[C.FunctionIdx].getBenefit() < 1) {
prune(C, FunctionList);
return true;
}
// C is in the list, and F is still beneficial.
return false;
};
// TODO: Experiment with interval trees or other interval-checking structures
// to lower the time complexity of this function.
// TODO: Can we do better than the simple greedy choice?
// Check for overlaps in the range.
// This is O(MaxCandidateLen * CandidateList.size()).
for (auto It = CandidateList.begin(), Et = CandidateList.end(); It != Et;
It++) {
Candidate &C1 = **It;
// If C1 was already pruned, or its function is no longer beneficial for
// outlining, move to the next candidate.
if (ShouldSkipCandidate(C1))
continue;
// The minimum start index of any candidate that could overlap with this
// one.
unsigned FarthestPossibleIdx = 0;
// Either the index is 0, or it's at most MaxCandidateLen indices away.
if (C1.getStartIdx() > MaxCandidateLen)
FarthestPossibleIdx = C1.getStartIdx() - MaxCandidateLen;
// Compare against the candidates in the list that start at most
// FarthestPossibleIdx indices away from C1. There are at most
// MaxCandidateLen of these.
for (auto Sit = It + 1; Sit != Et; Sit++) {
Candidate &C2 = **Sit;
// Is this candidate too far away to overlap?
if (C2.getStartIdx() < FarthestPossibleIdx)
break;
// If C2 was already pruned, or its function is no longer beneficial for
// outlining, move to the next candidate.
if (ShouldSkipCandidate(C2))
continue;
// Do C1 and C2 overlap?
//
// Not overlapping:
// High indices... [C1End ... C1Start][C2End ... C2Start] ...Low indices
//
// We sorted our candidate list so C2Start <= C1Start. We know that
// C2End > C2Start since each candidate has length >= 2. Therefore, all we
// have to check is C2End < C2Start to see if we overlap.
if (C2.getEndIdx() < C1.getStartIdx())
continue;
// C1 and C2 overlap.
// We need to choose the better of the two.
//
// Approximate this by picking the one which would have saved us the
// most instructions before any pruning.
// Is C2 a better candidate?
if (C2.Benefit > C1.Benefit) {
// Yes, so prune C1. Since C1 is dead, we don't have to compare it
// against anything anymore, so break.
prune(C1, FunctionList);
break;
}
// Prune C2 and move on to the next candidate.
prune(C2, FunctionList);
}
}
}
unsigned MachineOutliner::buildCandidateList(
std::vector<std::shared_ptr<Candidate>> &CandidateList,
std::vector<OutlinedFunction> &FunctionList, SuffixTree &ST,
InstructionMapper &Mapper, const TargetInstrInfo &TII) {
std::vector<unsigned> CandidateSequence; // Current outlining candidate.
unsigned MaxCandidateLen = 0; // Length of the longest candidate.
MaxCandidateLen =
findCandidates(ST, TII, Mapper, CandidateList, FunctionList);
// Sort the candidates in decending order. This will simplify the outlining
// process when we have to remove the candidates from the mapping by
// allowing us to cut them out without keeping track of an offset.
std::stable_sort(
CandidateList.begin(), CandidateList.end(),
[](const std::shared_ptr<Candidate> &LHS,
const std::shared_ptr<Candidate> &RHS) { return *LHS < *RHS; });
return MaxCandidateLen;
}
MachineFunction *
MachineOutliner::createOutlinedFunction(Module &M, const OutlinedFunction &OF,
InstructionMapper &Mapper) {
// Create the function name. This should be unique. For now, just hash the
// module name and include it in the function name plus the number of this
// function.
std::ostringstream NameStream;
NameStream << "OUTLINED_FUNCTION_" << OF.Name;
// Create the function using an IR-level function.
LLVMContext &C = M.getContext();
Function *F = dyn_cast<Function>(
M.getOrInsertFunction(NameStream.str(), Type::getVoidTy(C)));
assert(F && "Function was null!");
// NOTE: If this is linkonceodr, then we can take advantage of linker deduping
// which gives us better results when we outline from linkonceodr functions.
F->setLinkage(GlobalValue::InternalLinkage);
F->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
// Save F so that we can add debug info later if we need to.
CreatedIRFunctions.push_back(F);
BasicBlock *EntryBB = BasicBlock::Create(C, "entry", F);
IRBuilder<> Builder(EntryBB);
Builder.CreateRetVoid();
MachineModuleInfo &MMI = getAnalysis<MachineModuleInfo>();
MachineFunction &MF = MMI.getOrCreateMachineFunction(*F);
MachineBasicBlock &MBB = *MF.CreateMachineBasicBlock();
const TargetSubtargetInfo &STI = MF.getSubtarget();
const TargetInstrInfo &TII = *STI.getInstrInfo();
// Insert the new function into the module.
MF.insert(MF.begin(), &MBB);
TII.insertOutlinerPrologue(MBB, MF, OF.MInfo);
// Copy over the instructions for the function using the integer mappings in
// its sequence.
for (unsigned Str : OF.Sequence) {
MachineInstr *NewMI =
MF.CloneMachineInstr(Mapper.IntegerInstructionMap.find(Str)->second);
NewMI->dropMemRefs();
// Don't keep debug information for outlined instructions.
NewMI->setDebugLoc(DebugLoc());
MBB.insert(MBB.end(), NewMI);
}
TII.insertOutlinerEpilogue(MBB, MF, OF.MInfo);
// If there's a DISubprogram associated with this outlined function, then
// emit debug info for the outlined function.
if (DISubprogram *SP = OF.getSubprogramOrNull()) {
// We have a DISubprogram. Get its DICompileUnit.
DICompileUnit *CU = SP->getUnit();
DIBuilder DB(M, true, CU);
DIFile *Unit = SP->getFile();
Mangler Mg;
// Walk over each IR function we created in the outliner and create
// DISubprograms for each function.
for (Function *F : CreatedIRFunctions) {
// Get the mangled name of the function for the linkage name.
std::string Dummy;
llvm::raw_string_ostream MangledNameStream(Dummy);
Mg.getNameWithPrefix(MangledNameStream, F, false);
DISubprogram *SP = DB.createFunction(
Unit /* Context */, F->getName(), StringRef(MangledNameStream.str()),
Unit /* File */,
0 /* Line 0 is reserved for compiler-generated code. */,
DB.createSubroutineType(
DB.getOrCreateTypeArray(None)), /* void type */
false, true, 0, /* Line 0 is reserved for compiler-generated code. */
DINode::DIFlags::FlagArtificial /* Compiler-generated code. */,
true /* Outlined code is optimized code by definition. */);
// Don't add any new variables to the subprogram.
DB.finalizeSubprogram(SP);
// Attach subprogram to the function.
F->setSubprogram(SP);
}
// We're done with the DIBuilder.
DB.finalize();
}
MF.getRegInfo().freezeReservedRegs(MF);
return &MF;
}
bool MachineOutliner::outline(
Module &M, const ArrayRef<std::shared_ptr<Candidate>> &CandidateList,
std::vector<OutlinedFunction> &FunctionList, InstructionMapper &Mapper) {
bool OutlinedSomething = false;
// Replace the candidates with calls to their respective outlined functions.
for (const std::shared_ptr<Candidate> &Cptr : CandidateList) {
Candidate &C = *Cptr;
// Was the candidate removed during pruneOverlaps?
if (!C.InCandidateList)
continue;
// If not, then look at its OutlinedFunction.
OutlinedFunction &OF = FunctionList[C.FunctionIdx];
// Was its OutlinedFunction made unbeneficial during pruneOverlaps?
if (OF.getBenefit() < 1)
continue;
// If not, then outline it.
assert(C.getStartIdx() < Mapper.InstrList.size() &&
"Candidate out of bounds!");
MachineBasicBlock *MBB = (*Mapper.InstrList[C.getStartIdx()]).getParent();
MachineBasicBlock::iterator StartIt = Mapper.InstrList[C.getStartIdx()];
unsigned EndIdx = C.getEndIdx();
assert(EndIdx < Mapper.InstrList.size() && "Candidate out of bounds!");
MachineBasicBlock::iterator EndIt = Mapper.InstrList[EndIdx];
assert(EndIt != MBB->end() && "EndIt out of bounds!");
EndIt++; // Erase needs one past the end index.
// Does this candidate have a function yet?
if (!OF.MF) {
OF.MF = createOutlinedFunction(M, OF, Mapper);
MachineBasicBlock *MBB = &*OF.MF->begin();
// Output a remark telling the user that an outlined function was created,
// and explaining where it came from.
MachineOptimizationRemarkEmitter MORE(*OF.MF, nullptr);
MachineOptimizationRemark R(DEBUG_TYPE, "OutlinedFunction",
MBB->findDebugLoc(MBB->begin()), MBB);
R << "Saved " << NV("OutliningBenefit", OF.getBenefit())
<< " instructions by "
<< "outlining " << NV("Length", OF.Sequence.size()) << " instructions "
<< "from " << NV("NumOccurrences", OF.getOccurrenceCount())
<< " locations. "
<< "(Found at: ";
// Tell the user the other places the candidate was found.
for (size_t i = 0, e = OF.Candidates.size(); i < e; i++) {
// Skip over things that were pruned.
if (!OF.Candidates[i]->InCandidateList)
continue;
R << NV(
(Twine("StartLoc") + Twine(i)).str(),
Mapper.InstrList[OF.Candidates[i]->getStartIdx()]->getDebugLoc());
if (i != e - 1)
R << ", ";
}
R << ")";
MORE.emit(R);
FunctionsCreated++;
}
MachineFunction *MF = OF.MF;
const TargetSubtargetInfo &STI = MF->getSubtarget();
const TargetInstrInfo &TII = *STI.getInstrInfo();
// Insert a call to the new function and erase the old sequence.
TII.insertOutlinedCall(M, *MBB, StartIt, *MF, C.MInfo);
StartIt = Mapper.InstrList[C.getStartIdx()];
MBB->erase(StartIt, EndIt);
OutlinedSomething = true;
// Statistics.
NumOutlined++;
}
DEBUG(dbgs() << "OutlinedSomething = " << OutlinedSomething << "\n";);
return OutlinedSomething;
}
bool MachineOutliner::runOnModule(Module &M) {
// Check if there's anything in the module. If it's empty, then there's
// nothing to outline.
if (M.empty())
return false;
MachineModuleInfo &MMI = getAnalysis<MachineModuleInfo>();
const TargetSubtargetInfo &STI =
MMI.getOrCreateMachineFunction(*M.begin()).getSubtarget();
const TargetRegisterInfo *TRI = STI.getRegisterInfo();
const TargetInstrInfo *TII = STI.getInstrInfo();
// Does the target implement the MachineOutliner? If it doesn't, quit here.
if (!TII->useMachineOutliner()) {
// No. So we're done.
DEBUG(dbgs()
<< "Skipping pass: Target does not support the MachineOutliner.\n");
return false;
}
InstructionMapper Mapper;
// Build instruction mappings for each function in the module. Start by
// iterating over each Function in M.
for (Function &F : M) {
// If there's nothing in F, then there's no reason to try and outline from
// it.
if (F.empty())
continue;
// There's something in F. Check if it has a MachineFunction associated with
// it.
MachineFunction *MF = MMI.getMachineFunction(F);
// If it doesn't, then there's nothing to outline from. Move to the next
// Function.
if (!MF)
continue;
// We have a MachineFunction. Ask the target if it's suitable for outlining.
// If it isn't, then move on to the next Function in the module.
if (!TII->isFunctionSafeToOutlineFrom(*MF, OutlineFromLinkOnceODRs))
continue;
// We have a function suitable for outlining. Iterate over every
// MachineBasicBlock in MF and try to map its instructions to a list of
// unsigned integers.
for (MachineBasicBlock &MBB : *MF) {
// If there isn't anything in MBB, then there's no point in outlining from
// it.
if (MBB.empty())
continue;
// Check if MBB could be the target of an indirect branch. If it is, then
// we don't want to outline from it.
if (MBB.hasAddressTaken())
continue;
// MBB is suitable for outlining. Map it to a list of unsigneds.
Mapper.convertToUnsignedVec(MBB, *TRI, *TII);
}
}
// Construct a suffix tree, use it to find candidates, and then outline them.
SuffixTree ST(Mapper.UnsignedVec);
std::vector<std::shared_ptr<Candidate>> CandidateList;
std::vector<OutlinedFunction> FunctionList;
// Find all of the outlining candidates.
unsigned MaxCandidateLen =
buildCandidateList(CandidateList, FunctionList, ST, Mapper, *TII);
// Remove candidates that overlap with other candidates.
pruneOverlaps(CandidateList, FunctionList, Mapper, MaxCandidateLen, *TII);
// Outline each of the candidates and return true if something was outlined.
bool OutlinedSomething = outline(M, CandidateList, FunctionList, Mapper);
return OutlinedSomething;
}
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