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llvm-6502/lib/CodeGen/StrongPHIElimination.cpp
Owen Anderson 2ab36d3502 Begin adding static dependence information to passes, which will allow us to 
perform initialization without static constructors AND without explicit initialization
by the client.  For the moment, passes are required to initialize both their
(potential) dependencies and any passes they preserve.  I hope to be able to relax
the latter requirement in the future.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116334 91177308-0d34-0410-b5e6-96231b3b80d8
2010-10-12 19:48:12 +00:00

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//===- StrongPhiElimination.cpp - Eliminate PHI nodes by inserting copies -===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass eliminates machine instruction PHI nodes by inserting copy
// instructions, using an intelligent copy-folding technique based on
// dominator information. This is technique is derived from:
//
// Budimlic, et al. Fast copy coalescing and live-range identification.
// In Proceedings of the ACM SIGPLAN 2002 Conference on Programming Language
// Design and Implementation (Berlin, Germany, June 17 - 19, 2002).
// PLDI '02. ACM, New York, NY, 25-32.
// DOI= http://doi.acm.org/10.1145/512529.512534
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "strongphielim"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterCoalescer.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
namespace {
struct StrongPHIElimination : public MachineFunctionPass {
static char ID; // Pass identification, replacement for typeid
StrongPHIElimination() : MachineFunctionPass(ID) {}
// Waiting stores, for each MBB, the set of copies that need to
// be inserted into that MBB
DenseMap<MachineBasicBlock*,
std::multimap<unsigned, unsigned> > Waiting;
// Stacks holds the renaming stack for each register
std::map<unsigned, std::vector<unsigned> > Stacks;
// Registers in UsedByAnother are PHI nodes that are themselves
// used as operands to another PHI node
std::set<unsigned> UsedByAnother;
// RenameSets are the is a map from a PHI-defined register
// to the input registers to be coalesced along with the
// predecessor block for those input registers.
std::map<unsigned, std::map<unsigned, MachineBasicBlock*> > RenameSets;
// PhiValueNumber holds the ID numbers of the VNs for each phi that we're
// eliminating, indexed by the register defined by that phi.
std::map<unsigned, unsigned> PhiValueNumber;
// Store the DFS-in number of each block
DenseMap<MachineBasicBlock*, unsigned> preorder;
// Store the DFS-out number of each block
DenseMap<MachineBasicBlock*, unsigned> maxpreorder;
bool runOnMachineFunction(MachineFunction &Fn);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<MachineDominatorTree>();
AU.addRequired<SlotIndexes>();
AU.addPreserved<SlotIndexes>();
AU.addRequired<LiveIntervals>();
// TODO: Actually make this true.
AU.addPreserved<LiveIntervals>();
AU.addPreserved<RegisterCoalescer>();
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual void releaseMemory() {
preorder.clear();
maxpreorder.clear();
Waiting.clear();
Stacks.clear();
UsedByAnother.clear();
RenameSets.clear();
}
private:
/// DomForestNode - Represents a node in the "dominator forest". This is
/// a forest in which the nodes represent registers and the edges
/// represent a dominance relation in the block defining those registers.
struct DomForestNode {
private:
// Store references to our children
std::vector<DomForestNode*> children;
// The register we represent
unsigned reg;
// Add another node as our child
void addChild(DomForestNode* DFN) { children.push_back(DFN); }
public:
typedef std::vector<DomForestNode*>::iterator iterator;
// Create a DomForestNode by providing the register it represents, and
// the node to be its parent. The virtual root node has register 0
// and a null parent.
DomForestNode(unsigned r, DomForestNode* parent) : reg(r) {
if (parent)
parent->addChild(this);
}
~DomForestNode() {
for (iterator I = begin(), E = end(); I != E; ++I)
delete *I;
}
/// getReg - Return the regiser that this node represents
inline unsigned getReg() { return reg; }
// Provide iterator access to our children
inline DomForestNode::iterator begin() { return children.begin(); }
inline DomForestNode::iterator end() { return children.end(); }
};
void computeDFS(MachineFunction& MF);
void processBlock(MachineBasicBlock* MBB);
std::vector<DomForestNode*> computeDomForest(
std::map<unsigned, MachineBasicBlock*>& instrs,
MachineRegisterInfo& MRI);
void processPHIUnion(MachineInstr* Inst,
std::map<unsigned, MachineBasicBlock*>& PHIUnion,
std::vector<StrongPHIElimination::DomForestNode*>& DF,
std::vector<std::pair<unsigned, unsigned> >& locals);
void ScheduleCopies(MachineBasicBlock* MBB, std::set<unsigned>& pushed);
void InsertCopies(MachineDomTreeNode* MBB,
SmallPtrSet<MachineBasicBlock*, 16>& v);
bool mergeLiveIntervals(unsigned primary, unsigned secondary);
};
}
char StrongPHIElimination::ID = 0;
INITIALIZE_PASS_BEGIN(StrongPHIElimination, "strong-phi-node-elimination",
"Eliminate PHI nodes for register allocation, intelligently", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_END(StrongPHIElimination, "strong-phi-node-elimination",
"Eliminate PHI nodes for register allocation, intelligently", false, false)
char &llvm::StrongPHIEliminationID = StrongPHIElimination::ID;
/// computeDFS - Computes the DFS-in and DFS-out numbers of the dominator tree
/// of the given MachineFunction. These numbers are then used in other parts
/// of the PHI elimination process.
void StrongPHIElimination::computeDFS(MachineFunction& MF) {
SmallPtrSet<MachineDomTreeNode*, 8> frontier;
SmallPtrSet<MachineDomTreeNode*, 8> visited;
unsigned time = 0;
MachineDominatorTree& DT = getAnalysis<MachineDominatorTree>();
MachineDomTreeNode* node = DT.getRootNode();
std::vector<MachineDomTreeNode*> worklist;
worklist.push_back(node);
while (!worklist.empty()) {
MachineDomTreeNode* currNode = worklist.back();
if (!frontier.count(currNode)) {
frontier.insert(currNode);
++time;
preorder.insert(std::make_pair(currNode->getBlock(), time));
}
bool inserted = false;
for (MachineDomTreeNode::iterator I = currNode->begin(), E = currNode->end();
I != E; ++I)
if (!frontier.count(*I) && !visited.count(*I)) {
worklist.push_back(*I);
inserted = true;
break;
}
if (!inserted) {
frontier.erase(currNode);
visited.insert(currNode);
maxpreorder.insert(std::make_pair(currNode->getBlock(), time));
worklist.pop_back();
}
}
}
namespace {
/// PreorderSorter - a helper class that is used to sort registers
/// according to the preorder number of their defining blocks
class PreorderSorter {
private:
DenseMap<MachineBasicBlock*, unsigned>& preorder;
MachineRegisterInfo& MRI;
public:
PreorderSorter(DenseMap<MachineBasicBlock*, unsigned>& p,
MachineRegisterInfo& M) : preorder(p), MRI(M) { }
bool operator()(unsigned A, unsigned B) {
if (A == B)
return false;
MachineBasicBlock* ABlock = MRI.getVRegDef(A)->getParent();
MachineBasicBlock* BBlock = MRI.getVRegDef(B)->getParent();
if (preorder[ABlock] < preorder[BBlock])
return true;
else if (preorder[ABlock] > preorder[BBlock])
return false;
return false;
}
};
}
/// computeDomForest - compute the subforest of the DomTree corresponding
/// to the defining blocks of the registers in question
std::vector<StrongPHIElimination::DomForestNode*>
StrongPHIElimination::computeDomForest(
std::map<unsigned, MachineBasicBlock*>& regs,
MachineRegisterInfo& MRI) {
// Begin by creating a virtual root node, since the actual results
// may well be a forest. Assume this node has maximum DFS-out number.
DomForestNode* VirtualRoot = new DomForestNode(0, 0);
maxpreorder.insert(std::make_pair((MachineBasicBlock*)0, ~0UL));
// Populate a worklist with the registers
std::vector<unsigned> worklist;
worklist.reserve(regs.size());
for (std::map<unsigned, MachineBasicBlock*>::iterator I = regs.begin(),
E = regs.end(); I != E; ++I)
worklist.push_back(I->first);
// Sort the registers by the DFS-in number of their defining block
PreorderSorter PS(preorder, MRI);
std::sort(worklist.begin(), worklist.end(), PS);
// Create a "current parent" stack, and put the virtual root on top of it
DomForestNode* CurrentParent = VirtualRoot;
std::vector<DomForestNode*> stack;
stack.push_back(VirtualRoot);
// Iterate over all the registers in the previously computed order
for (std::vector<unsigned>::iterator I = worklist.begin(), E = worklist.end();
I != E; ++I) {
unsigned pre = preorder[MRI.getVRegDef(*I)->getParent()];
MachineBasicBlock* parentBlock = CurrentParent->getReg() ?
MRI.getVRegDef(CurrentParent->getReg())->getParent() :
0;
// If the DFS-in number of the register is greater than the DFS-out number
// of the current parent, repeatedly pop the parent stack until it isn't.
while (pre > maxpreorder[parentBlock]) {
stack.pop_back();
CurrentParent = stack.back();
parentBlock = CurrentParent->getReg() ?
MRI.getVRegDef(CurrentParent->getReg())->getParent() :
0;
}
// Now that we've found the appropriate parent, create a DomForestNode for
// this register and attach it to the forest
DomForestNode* child = new DomForestNode(*I, CurrentParent);
// Push this new node on the "current parent" stack
stack.push_back(child);
CurrentParent = child;
}
// Return a vector containing the children of the virtual root node
std::vector<DomForestNode*> ret;
ret.insert(ret.end(), VirtualRoot->begin(), VirtualRoot->end());
return ret;
}
/// isLiveIn - helper method that determines, from a regno, if a register
/// is live into a block
static bool isLiveIn(unsigned r, MachineBasicBlock* MBB,
LiveIntervals& LI) {
LiveInterval& I = LI.getOrCreateInterval(r);
SlotIndex idx = LI.getMBBStartIdx(MBB);
return I.liveAt(idx);
}
/// isLiveOut - help method that determines, from a regno, if a register is
/// live out of a block.
static bool isLiveOut(unsigned r, MachineBasicBlock* MBB,
LiveIntervals& LI) {
for (MachineBasicBlock::succ_iterator PI = MBB->succ_begin(),
E = MBB->succ_end(); PI != E; ++PI)
if (isLiveIn(r, *PI, LI))
return true;
return false;
}
/// interferes - checks for local interferences by scanning a block. The only
/// trick parameter is 'mode' which tells it the relationship of the two
/// registers. 0 - defined in the same block, 1 - first properly dominates
/// second, 2 - second properly dominates first
static bool interferes(unsigned a, unsigned b, MachineBasicBlock* scan,
LiveIntervals& LV, unsigned mode) {
MachineInstr* def = 0;
MachineInstr* kill = 0;
// The code is still in SSA form at this point, so there is only one
// definition per VReg. Thus we can safely use MRI->getVRegDef().
const MachineRegisterInfo* MRI = &scan->getParent()->getRegInfo();
bool interference = false;
// Wallk the block, checking for interferences
for (MachineBasicBlock::iterator MBI = scan->begin(), MBE = scan->end();
MBI != MBE; ++MBI) {
MachineInstr* curr = MBI;
// Same defining block...
if (mode == 0) {
if (curr == MRI->getVRegDef(a)) {
// If we find our first definition, save it
if (!def) {
def = curr;
// If there's already an unkilled definition, then
// this is an interference
} else if (!kill) {
interference = true;
break;
// If there's a definition followed by a KillInst, then
// they can't interfere
} else {
interference = false;
break;
}
// Symmetric with the above
} else if (curr == MRI->getVRegDef(b)) {
if (!def) {
def = curr;
} else if (!kill) {
interference = true;
break;
} else {
interference = false;
break;
}
// Store KillInsts if they match up with the definition
} else if (curr->killsRegister(a)) {
if (def == MRI->getVRegDef(a)) {
kill = curr;
} else if (curr->killsRegister(b)) {
if (def == MRI->getVRegDef(b)) {
kill = curr;
}
}
}
// First properly dominates second...
} else if (mode == 1) {
if (curr == MRI->getVRegDef(b)) {
// Definition of second without kill of first is an interference
if (!kill) {
interference = true;
break;
// Definition after a kill is a non-interference
} else {
interference = false;
break;
}
// Save KillInsts of First
} else if (curr->killsRegister(a)) {
kill = curr;
}
// Symmetric with the above
} else if (mode == 2) {
if (curr == MRI->getVRegDef(a)) {
if (!kill) {
interference = true;
break;
} else {
interference = false;
break;
}
} else if (curr->killsRegister(b)) {
kill = curr;
}
}
}
return interference;
}
/// processBlock - Determine how to break up PHIs in the current block. Each
/// PHI is broken up by some combination of renaming its operands and inserting
/// copies. This method is responsible for determining which operands receive
/// which treatment.
void StrongPHIElimination::processBlock(MachineBasicBlock* MBB) {
LiveIntervals& LI = getAnalysis<LiveIntervals>();
MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo();
// Holds names that have been added to a set in any PHI within this block
// before the current one.
std::set<unsigned> ProcessedNames;
// Iterate over all the PHI nodes in this block
MachineBasicBlock::iterator P = MBB->begin();
while (P != MBB->end() && P->isPHI()) {
unsigned DestReg = P->getOperand(0).getReg();
// Don't both doing PHI elimination for dead PHI's.
if (P->registerDefIsDead(DestReg)) {
++P;
continue;
}
LiveInterval& PI = LI.getOrCreateInterval(DestReg);
SlotIndex pIdx = LI.getInstructionIndex(P).getDefIndex();
VNInfo* PVN = PI.getLiveRangeContaining(pIdx)->valno;
PhiValueNumber.insert(std::make_pair(DestReg, PVN->id));
// PHIUnion is the set of incoming registers to the PHI node that
// are going to be renames rather than having copies inserted. This set
// is refinded over the course of this function. UnionedBlocks is the set
// of corresponding MBBs.
std::map<unsigned, MachineBasicBlock*> PHIUnion;
SmallPtrSet<MachineBasicBlock*, 8> UnionedBlocks;
// Iterate over the operands of the PHI node
for (int i = P->getNumOperands() - 1; i >= 2; i-=2) {
unsigned SrcReg = P->getOperand(i-1).getReg();
// Don't need to try to coalesce a register with itself.
if (SrcReg == DestReg) {
ProcessedNames.insert(SrcReg);
continue;
}
// We don't need to insert copies for implicit_defs.
MachineInstr* DefMI = MRI.getVRegDef(SrcReg);
if (DefMI->isImplicitDef())
ProcessedNames.insert(SrcReg);
// Check for trivial interferences via liveness information, allowing us
// to avoid extra work later. Any registers that interfere cannot both
// be in the renaming set, so choose one and add copies for it instead.
// The conditions are:
// 1) if the operand is live into the PHI node's block OR
// 2) if the PHI node is live out of the operand's defining block OR
// 3) if the operand is itself a PHI node and the original PHI is
// live into the operand's defining block OR
// 4) if the operand is already being renamed for another PHI node
// in this block OR
// 5) if any two operands are defined in the same block, insert copies
// for one of them
if (isLiveIn(SrcReg, P->getParent(), LI) ||
isLiveOut(P->getOperand(0).getReg(),
MRI.getVRegDef(SrcReg)->getParent(), LI) ||
( MRI.getVRegDef(SrcReg)->isPHI() &&
isLiveIn(P->getOperand(0).getReg(),
MRI.getVRegDef(SrcReg)->getParent(), LI) ) ||
ProcessedNames.count(SrcReg) ||
UnionedBlocks.count(MRI.getVRegDef(SrcReg)->getParent())) {
// Add a copy for the selected register
MachineBasicBlock* From = P->getOperand(i).getMBB();
Waiting[From].insert(std::make_pair(SrcReg, DestReg));
UsedByAnother.insert(SrcReg);
} else {
// Otherwise, add it to the renaming set
PHIUnion.insert(std::make_pair(SrcReg,P->getOperand(i).getMBB()));
UnionedBlocks.insert(MRI.getVRegDef(SrcReg)->getParent());
}
}
// Compute the dominator forest for the renaming set. This is a forest
// where the nodes are the registers and the edges represent dominance
// relations between the defining blocks of the registers
std::vector<StrongPHIElimination::DomForestNode*> DF =
computeDomForest(PHIUnion, MRI);
// Walk DomForest to resolve interferences at an inter-block level. This
// will remove registers from the renaming set (and insert copies for them)
// if interferences are found.
std::vector<std::pair<unsigned, unsigned> > localInterferences;
processPHIUnion(P, PHIUnion, DF, localInterferences);
// If one of the inputs is defined in the same block as the current PHI
// then we need to check for a local interference between that input and
// the PHI.
for (std::map<unsigned, MachineBasicBlock*>::iterator I = PHIUnion.begin(),
E = PHIUnion.end(); I != E; ++I)
if (MRI.getVRegDef(I->first)->getParent() == P->getParent())
localInterferences.push_back(std::make_pair(I->first,
P->getOperand(0).getReg()));
// The dominator forest walk may have returned some register pairs whose
// interference cannot be determined from dominator analysis. We now
// examine these pairs for local interferences.
for (std::vector<std::pair<unsigned, unsigned> >::iterator I =
localInterferences.begin(), E = localInterferences.end(); I != E; ++I) {
std::pair<unsigned, unsigned> p = *I;
MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
// Determine the block we need to scan and the relationship between
// the two registers
MachineBasicBlock* scan = 0;
unsigned mode = 0;
if (MRI.getVRegDef(p.first)->getParent() ==
MRI.getVRegDef(p.second)->getParent()) {
scan = MRI.getVRegDef(p.first)->getParent();
mode = 0; // Same block
} else if (MDT.dominates(MRI.getVRegDef(p.first)->getParent(),
MRI.getVRegDef(p.second)->getParent())) {
scan = MRI.getVRegDef(p.second)->getParent();
mode = 1; // First dominates second
} else {
scan = MRI.getVRegDef(p.first)->getParent();
mode = 2; // Second dominates first
}
// If there's an interference, we need to insert copies
if (interferes(p.first, p.second, scan, LI, mode)) {
// Insert copies for First
for (int i = P->getNumOperands() - 1; i >= 2; i-=2) {
if (P->getOperand(i-1).getReg() == p.first) {
unsigned SrcReg = p.first;
MachineBasicBlock* From = P->getOperand(i).getMBB();
Waiting[From].insert(std::make_pair(SrcReg,
P->getOperand(0).getReg()));
UsedByAnother.insert(SrcReg);
PHIUnion.erase(SrcReg);
}
}
}
}
// Add the renaming set for this PHI node to our overall renaming information
for (std::map<unsigned, MachineBasicBlock*>::iterator QI = PHIUnion.begin(),
QE = PHIUnion.end(); QI != QE; ++QI) {
DEBUG(dbgs() << "Adding Renaming: " << QI->first << " -> "
<< P->getOperand(0).getReg() << "\n");
}
RenameSets.insert(std::make_pair(P->getOperand(0).getReg(), PHIUnion));
// Remember which registers are already renamed, so that we don't try to
// rename them for another PHI node in this block
for (std::map<unsigned, MachineBasicBlock*>::iterator I = PHIUnion.begin(),
E = PHIUnion.end(); I != E; ++I)
ProcessedNames.insert(I->first);
++P;
}
}
/// processPHIUnion - Take a set of candidate registers to be coalesced when
/// decomposing the PHI instruction. Use the DominanceForest to remove the ones
/// that are known to interfere, and flag others that need to be checked for
/// local interferences.
void StrongPHIElimination::processPHIUnion(MachineInstr* Inst,
std::map<unsigned, MachineBasicBlock*>& PHIUnion,
std::vector<StrongPHIElimination::DomForestNode*>& DF,
std::vector<std::pair<unsigned, unsigned> >& locals) {
std::vector<DomForestNode*> worklist(DF.begin(), DF.end());
SmallPtrSet<DomForestNode*, 4> visited;
// Code is still in SSA form, so we can use MRI::getVRegDef()
MachineRegisterInfo& MRI = Inst->getParent()->getParent()->getRegInfo();
LiveIntervals& LI = getAnalysis<LiveIntervals>();
unsigned DestReg = Inst->getOperand(0).getReg();
// DF walk on the DomForest
while (!worklist.empty()) {
DomForestNode* DFNode = worklist.back();
visited.insert(DFNode);
bool inserted = false;
for (DomForestNode::iterator CI = DFNode->begin(), CE = DFNode->end();
CI != CE; ++CI) {
DomForestNode* child = *CI;
// If the current node is live-out of the defining block of one of its
// children, insert a copy for it. NOTE: The paper actually calls for
// a more elaborate heuristic for determining whether to insert copies
// for the child or the parent. In the interest of simplicity, we're
// just always choosing the parent.
if (isLiveOut(DFNode->getReg(),
MRI.getVRegDef(child->getReg())->getParent(), LI)) {
// Insert copies for parent
for (int i = Inst->getNumOperands() - 1; i >= 2; i-=2) {
if (Inst->getOperand(i-1).getReg() == DFNode->getReg()) {
unsigned SrcReg = DFNode->getReg();
MachineBasicBlock* From = Inst->getOperand(i).getMBB();
Waiting[From].insert(std::make_pair(SrcReg, DestReg));
UsedByAnother.insert(SrcReg);
PHIUnion.erase(SrcReg);
}
}
// If a node is live-in to the defining block of one of its children, but
// not live-out, then we need to scan that block for local interferences.
} else if (isLiveIn(DFNode->getReg(),
MRI.getVRegDef(child->getReg())->getParent(), LI) ||
MRI.getVRegDef(DFNode->getReg())->getParent() ==
MRI.getVRegDef(child->getReg())->getParent()) {
// Add (p, c) to possible local interferences
locals.push_back(std::make_pair(DFNode->getReg(), child->getReg()));
}
if (!visited.count(child)) {
worklist.push_back(child);
inserted = true;
}
}
if (!inserted) worklist.pop_back();
}
}
/// ScheduleCopies - Insert copies into predecessor blocks, scheduling
/// them properly so as to avoid the 'lost copy' and the 'virtual swap'
/// problems.
///
/// Based on "Practical Improvements to the Construction and Destruction
/// of Static Single Assignment Form" by Briggs, et al.
void StrongPHIElimination::ScheduleCopies(MachineBasicBlock* MBB,
std::set<unsigned>& pushed) {
// FIXME: This function needs to update LiveIntervals
std::multimap<unsigned, unsigned>& copy_set= Waiting[MBB];
std::multimap<unsigned, unsigned> worklist;
std::map<unsigned, unsigned> map;
// Setup worklist of initial copies
for (std::multimap<unsigned, unsigned>::iterator I = copy_set.begin(),
E = copy_set.end(); I != E; ) {
map.insert(std::make_pair(I->first, I->first));
map.insert(std::make_pair(I->second, I->second));
if (!UsedByAnother.count(I->second)) {
worklist.insert(*I);
// Avoid iterator invalidation
std::multimap<unsigned, unsigned>::iterator OI = I;
++I;
copy_set.erase(OI);
} else {
++I;
}
}
LiveIntervals& LI = getAnalysis<LiveIntervals>();
MachineFunction* MF = MBB->getParent();
MachineRegisterInfo& MRI = MF->getRegInfo();
const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
SmallVector<std::pair<unsigned, MachineInstr*>, 4> InsertedPHIDests;
// Iterate over the worklist, inserting copies
while (!worklist.empty() || !copy_set.empty()) {
while (!worklist.empty()) {
std::multimap<unsigned, unsigned>::iterator WI = worklist.begin();
std::pair<unsigned, unsigned> curr = *WI;
worklist.erase(WI);
const TargetRegisterClass *RC = MF->getRegInfo().getRegClass(curr.first);
if (isLiveOut(curr.second, MBB, LI)) {
// Create a temporary
unsigned t = MF->getRegInfo().createVirtualRegister(RC);
// Insert copy from curr.second to a temporary at
// the Phi defining curr.second
MachineBasicBlock::iterator PI = MRI.getVRegDef(curr.second);
BuildMI(*PI->getParent(), PI, DebugLoc(), TII->get(TargetOpcode::COPY),
t).addReg(curr.second);
DEBUG(dbgs() << "Inserted copy from " << curr.second << " to " << t
<< "\n");
// Push temporary on Stacks
Stacks[curr.second].push_back(t);
// Insert curr.second in pushed
pushed.insert(curr.second);
// Create a live interval for this temporary
InsertedPHIDests.push_back(std::make_pair(t, --PI));
}
// Insert copy from map[curr.first] to curr.second
BuildMI(*MBB, MBB->getFirstTerminator(), DebugLoc(),
TII->get(TargetOpcode::COPY), curr.second).addReg(map[curr.first]);
map[curr.first] = curr.second;
DEBUG(dbgs() << "Inserted copy from " << curr.first << " to "
<< curr.second << "\n");
// Push this copy onto InsertedPHICopies so we can
// update LiveIntervals with it.
MachineBasicBlock::iterator MI = MBB->getFirstTerminator();
InsertedPHIDests.push_back(std::make_pair(curr.second, --MI));
// If curr.first is a destination in copy_set...
for (std::multimap<unsigned, unsigned>::iterator I = copy_set.begin(),
E = copy_set.end(); I != E; )
if (curr.first == I->second) {
std::pair<unsigned, unsigned> temp = *I;
worklist.insert(temp);
// Avoid iterator invalidation
std::multimap<unsigned, unsigned>::iterator OI = I;
++I;
copy_set.erase(OI);
break;
} else {
++I;
}
}
if (!copy_set.empty()) {
std::multimap<unsigned, unsigned>::iterator CI = copy_set.begin();
std::pair<unsigned, unsigned> curr = *CI;
worklist.insert(curr);
copy_set.erase(CI);
LiveInterval& I = LI.getInterval(curr.second);
MachineBasicBlock::iterator term = MBB->getFirstTerminator();
SlotIndex endIdx = SlotIndex();
if (term != MBB->end())
endIdx = LI.getInstructionIndex(term);
else
endIdx = LI.getMBBEndIdx(MBB);
if (I.liveAt(endIdx)) {
const TargetRegisterClass *RC =
MF->getRegInfo().getRegClass(curr.first);
// Insert a copy from dest to a new temporary t at the end of b
unsigned t = MF->getRegInfo().createVirtualRegister(RC);
BuildMI(*MBB, MBB->getFirstTerminator(), DebugLoc(),
TII->get(TargetOpcode::COPY), t).addReg(curr.second);
map[curr.second] = t;
MachineBasicBlock::iterator TI = MBB->getFirstTerminator();
InsertedPHIDests.push_back(std::make_pair(t, --TI));
}
}
}
// Renumber the instructions so that we can perform the index computations
// needed to create new live intervals.
LI.renumber();
// For copies that we inserted at the ends of predecessors, we construct
// live intervals. This is pretty easy, since we know that the destination
// register cannot have be in live at that point previously. We just have
// to make sure that, for registers that serve as inputs to more than one
// PHI, we don't create multiple overlapping live intervals.
std::set<unsigned> RegHandled;
for (SmallVector<std::pair<unsigned, MachineInstr*>, 4>::iterator I =
InsertedPHIDests.begin(), E = InsertedPHIDests.end(); I != E; ++I) {
if (RegHandled.insert(I->first).second) {
LiveInterval& Int = LI.getOrCreateInterval(I->first);
SlotIndex instrIdx = LI.getInstructionIndex(I->second);
if (Int.liveAt(instrIdx.getDefIndex()))
Int.removeRange(instrIdx.getDefIndex(),
LI.getMBBEndIdx(I->second->getParent()).getNextSlot(),
true);
LiveRange R = LI.addLiveRangeToEndOfBlock(I->first, I->second);
R.valno->setCopy(I->second);
R.valno->def = LI.getInstructionIndex(I->second).getDefIndex();
}
}
}
/// InsertCopies - insert copies into MBB and all of its successors
void StrongPHIElimination::InsertCopies(MachineDomTreeNode* MDTN,
SmallPtrSet<MachineBasicBlock*, 16>& visited) {
MachineBasicBlock* MBB = MDTN->getBlock();
visited.insert(MBB);
std::set<unsigned> pushed;
LiveIntervals& LI = getAnalysis<LiveIntervals>();
// Rewrite register uses from Stacks
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
I != E; ++I) {
if (I->isPHI())
continue;
for (unsigned i = 0; i < I->getNumOperands(); ++i)
if (I->getOperand(i).isReg() &&
Stacks[I->getOperand(i).getReg()].size()) {
// Remove the live range for the old vreg.
LiveInterval& OldInt = LI.getInterval(I->getOperand(i).getReg());
LiveInterval::iterator OldLR =
OldInt.FindLiveRangeContaining(LI.getInstructionIndex(I).getUseIndex());
if (OldLR != OldInt.end())
OldInt.removeRange(*OldLR, true);
// Change the register
I->getOperand(i).setReg(Stacks[I->getOperand(i).getReg()].back());
// Add a live range for the new vreg
LiveInterval& Int = LI.getInterval(I->getOperand(i).getReg());
VNInfo* FirstVN = *Int.vni_begin();
FirstVN->setHasPHIKill(false);
LiveRange LR (LI.getMBBStartIdx(I->getParent()),
LI.getInstructionIndex(I).getUseIndex().getNextSlot(),
FirstVN);
Int.addRange(LR);
}
}
// Schedule the copies for this block
ScheduleCopies(MBB, pushed);
// Recur down the dominator tree.
for (MachineDomTreeNode::iterator I = MDTN->begin(),
E = MDTN->end(); I != E; ++I)
if (!visited.count((*I)->getBlock()))
InsertCopies(*I, visited);
// As we exit this block, pop the names we pushed while processing it
for (std::set<unsigned>::iterator I = pushed.begin(),
E = pushed.end(); I != E; ++I)
Stacks[*I].pop_back();
}
bool StrongPHIElimination::mergeLiveIntervals(unsigned primary,
unsigned secondary) {
LiveIntervals& LI = getAnalysis<LiveIntervals>();
LiveInterval& LHS = LI.getOrCreateInterval(primary);
LiveInterval& RHS = LI.getOrCreateInterval(secondary);
LI.renumber();
DenseMap<VNInfo*, VNInfo*> VNMap;
for (LiveInterval::iterator I = RHS.begin(), E = RHS.end(); I != E; ++I) {
LiveRange R = *I;
SlotIndex Start = R.start;
SlotIndex End = R.end;
if (LHS.getLiveRangeContaining(Start))
return false;
if (LHS.getLiveRangeContaining(End))
return false;
LiveInterval::iterator RI = std::upper_bound(LHS.begin(), LHS.end(), R);
if (RI != LHS.end() && RI->start < End)
return false;
}
for (LiveInterval::iterator I = RHS.begin(), E = RHS.end(); I != E; ++I) {
LiveRange R = *I;
VNInfo* OldVN = R.valno;
VNInfo*& NewVN = VNMap[OldVN];
if (!NewVN) {
NewVN = LHS.createValueCopy(OldVN, LI.getVNInfoAllocator());
}
LiveRange LR (R.start, R.end, NewVN);
LHS.addRange(LR);
}
LI.removeInterval(RHS.reg);
return true;
}
bool StrongPHIElimination::runOnMachineFunction(MachineFunction &Fn) {
LiveIntervals& LI = getAnalysis<LiveIntervals>();
// Compute DFS numbers of each block
computeDFS(Fn);
// Determine which phi node operands need copies
for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
if (!I->empty() && I->begin()->isPHI())
processBlock(I);
// Break interferences where two different phis want to coalesce
// in the same register.
std::set<unsigned> seen;
typedef std::map<unsigned, std::map<unsigned, MachineBasicBlock*> >
RenameSetType;
for (RenameSetType::iterator I = RenameSets.begin(), E = RenameSets.end();
I != E; ++I) {
for (std::map<unsigned, MachineBasicBlock*>::iterator
OI = I->second.begin(), OE = I->second.end(); OI != OE; ) {
if (!seen.count(OI->first)) {
seen.insert(OI->first);
++OI;
} else {
Waiting[OI->second].insert(std::make_pair(OI->first, I->first));
unsigned reg = OI->first;
++OI;
I->second.erase(reg);
DEBUG(dbgs() << "Removing Renaming: " << reg << " -> " << I->first
<< "\n");
}
}
}
// Insert copies
// FIXME: This process should probably preserve LiveIntervals
SmallPtrSet<MachineBasicBlock*, 16> visited;
MachineDominatorTree& MDT = getAnalysis<MachineDominatorTree>();
InsertCopies(MDT.getRootNode(), visited);
// Perform renaming
for (RenameSetType::iterator I = RenameSets.begin(), E = RenameSets.end();
I != E; ++I)
while (I->second.size()) {
std::map<unsigned, MachineBasicBlock*>::iterator SI = I->second.begin();
DEBUG(dbgs() << "Renaming: " << SI->first << " -> " << I->first << "\n");
if (SI->first != I->first) {
if (mergeLiveIntervals(I->first, SI->first)) {
Fn.getRegInfo().replaceRegWith(SI->first, I->first);
if (RenameSets.count(SI->first)) {
I->second.insert(RenameSets[SI->first].begin(),
RenameSets[SI->first].end());
RenameSets.erase(SI->first);
}
} else {
// Insert a last-minute copy if a conflict was detected.
const TargetInstrInfo *TII = Fn.getTarget().getInstrInfo();
BuildMI(*SI->second, SI->second->getFirstTerminator(), DebugLoc(),
TII->get(TargetOpcode::COPY), I->first).addReg(SI->first);
LI.renumber();
LiveInterval& Int = LI.getOrCreateInterval(I->first);
SlotIndex instrIdx =
LI.getInstructionIndex(--SI->second->getFirstTerminator());
if (Int.liveAt(instrIdx.getDefIndex()))
Int.removeRange(instrIdx.getDefIndex(),
LI.getMBBEndIdx(SI->second).getNextSlot(), true);
LiveRange R = LI.addLiveRangeToEndOfBlock(I->first,
--SI->second->getFirstTerminator());
R.valno->setCopy(--SI->second->getFirstTerminator());
R.valno->def = instrIdx.getDefIndex();
DEBUG(dbgs() << "Renaming failed: " << SI->first << " -> "
<< I->first << "\n");
}
}
LiveInterval& Int = LI.getOrCreateInterval(I->first);
const LiveRange* LR =
Int.getLiveRangeContaining(LI.getMBBEndIdx(SI->second));
LR->valno->setHasPHIKill(true);
I->second.erase(SI->first);
}
// Remove PHIs
std::vector<MachineInstr*> phis;
for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
for (MachineBasicBlock::iterator BI = I->begin(), BE = I->end();
BI != BE; ++BI)
if (BI->isPHI())
phis.push_back(BI);
}
for (std::vector<MachineInstr*>::iterator I = phis.begin(), E = phis.end();
I != E; ) {
MachineInstr* PInstr = *(I++);
// If this is a dead PHI node, then remove it from LiveIntervals.
unsigned DestReg = PInstr->getOperand(0).getReg();
LiveInterval& PI = LI.getInterval(DestReg);
if (PInstr->registerDefIsDead(DestReg)) {
if (PI.containsOneValue()) {
LI.removeInterval(DestReg);
} else {
SlotIndex idx = LI.getInstructionIndex(PInstr).getDefIndex();
PI.removeRange(*PI.getLiveRangeContaining(idx), true);
}
} else {
// Trim live intervals of input registers. They are no longer live into
// this block if they died after the PHI. If they lived after it, don't
// trim them because they might have other legitimate uses.
for (unsigned i = 1; i < PInstr->getNumOperands(); i += 2) {
unsigned reg = PInstr->getOperand(i).getReg();
MachineBasicBlock* MBB = PInstr->getOperand(i+1).getMBB();
LiveInterval& InputI = LI.getInterval(reg);
if (MBB != PInstr->getParent() &&
InputI.liveAt(LI.getMBBStartIdx(PInstr->getParent())) &&
InputI.expiredAt(LI.getInstructionIndex(PInstr).getNextIndex()))
InputI.removeRange(LI.getMBBStartIdx(PInstr->getParent()),
LI.getInstructionIndex(PInstr),
true);
}
// If the PHI is not dead, then the valno defined by the PHI
// now has an unknown def.
SlotIndex idx = LI.getInstructionIndex(PInstr).getDefIndex();
const LiveRange* PLR = PI.getLiveRangeContaining(idx);
PLR->valno->setIsPHIDef(true);
LiveRange R (LI.getMBBStartIdx(PInstr->getParent()),
PLR->start, PLR->valno);
PI.addRange(R);
}
LI.RemoveMachineInstrFromMaps(PInstr);
PInstr->eraseFromParent();
}
LI.renumber();
return true;
}
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