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llvm-mirror/lib/CodeGen/StrongPHIElimination.cpp

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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/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/Compiler.h"
using namespace llvm;
namespace {
struct VISIBILITY_HIDDEN StrongPHIElimination : public MachineFunctionPass {
static char ID; // Pass identification, replacement for typeid
StrongPHIElimination() : MachineFunctionPass((intptr_t)&ID) {}
// Waiting stores, for each MBB, the set of copies that need to
// be inserted into that MBB
DenseMap<MachineBasicBlock*,
std::map<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 another PHI node
std::set<unsigned> UsedByAnother;
// RenameSets are the sets of operands (and their VNInfo IDs) to a PHI
// (the defining instruction of the key) that can be renamed without copies.
std::map<unsigned, std::map<unsigned, unsigned> > 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.addRequired<MachineDominatorTree>();
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, unsigned>& instrs,
MachineRegisterInfo& MRI);
void processPHIUnion(MachineInstr* Inst,
std::map<unsigned, unsigned>& PHIUnion,
std::vector<StrongPHIElimination::DomForestNode*>& DF,
std::vector<std::pair<unsigned, unsigned> >& locals);
void ScheduleCopies(MachineBasicBlock* MBB, std::set<unsigned>& pushed);
void InsertCopies(MachineBasicBlock* MBB,
SmallPtrSet<MachineBasicBlock*, 16>& v);
void mergeLiveIntervals(unsigned primary, unsigned secondary, unsigned VN);
};
}
char StrongPHIElimination::ID = 0;
static RegisterPass<StrongPHIElimination>
X("strong-phi-node-elimination",
"Eliminate PHI nodes for register allocation, intelligently");
const PassInfo *const llvm::StrongPHIEliminationID = &X;
/// 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, unsigned>& 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, unsigned>::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);
unsigned idx = LI.getMBBStartIdx(MBB);
return I.liveBeforeAndAt(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->getOpcode() == TargetInstrInfo::PHI) {
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);
unsigned pIdx = LI.getDefIndex(LI.getInstructionIndex(P));
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, unsigned> 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();
// 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)->getOpcode() == TargetInstrInfo::PHI &&
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
LiveInterval& I = LI.getOrCreateInterval(SrcReg);
unsigned idx = LI.getMBBEndIdx(P->getOperand(i).getMBB());
VNInfo* VN = I.getLiveRangeContaining(idx)->valno;
assert(VN && "No VNInfo for register?");
PHIUnion.insert(std::make_pair(SrcReg, VN->id));
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, unsigned>::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
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, unsigned>::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, unsigned>& 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 LiveVariables
std::map<unsigned, unsigned>& copy_set= Waiting[MBB];
std::map<unsigned, unsigned> worklist;
std::map<unsigned, unsigned> map;
// Setup worklist of initial copies
for (std::map<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
unsigned first = I->first;
++I;
copy_set.erase(first);
} else {
++I;
}
}
LiveIntervals& LI = getAnalysis<LiveIntervals>();
MachineFunction* MF = MBB->getParent();
MachineRegisterInfo& MRI = MF->getRegInfo();
const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
// Iterate over the worklist, inserting copies
while (!worklist.empty() || !copy_set.empty()) {
while (!worklist.empty()) {
std::pair<unsigned, unsigned> curr = *worklist.begin();
worklist.erase(curr.first);
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);
TII->copyRegToReg(*PI->getParent(), PI, t,
curr.second, RC, RC);
// Push temporary on Stacks
Stacks[curr.second].push_back(t);
// Insert curr.second in pushed
pushed.insert(curr.second);
}
// Insert copy from map[curr.first] to curr.second
TII->copyRegToReg(*MBB, MBB->getFirstTerminator(), curr.second,
map[curr.first], RC, RC);
map[curr.first] = curr.second;
// If curr.first is a destination in copy_set...
for (std::map<unsigned, unsigned>::iterator I = copy_set.begin(),
E = copy_set.end(); I != E; )
if (curr.first == I->second) {
std::pair<unsigned, unsigned> temp = *I;
// Avoid iterator invalidation
++I;
copy_set.erase(temp.first);
worklist.insert(temp);
break;
} else {
++I;
}
}
if (!copy_set.empty()) {
std::pair<unsigned, unsigned> curr = *copy_set.begin();
copy_set.erase(curr.first);
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);
TII->copyRegToReg(*MBB, MBB->getFirstTerminator(), t,
curr.second, RC, RC);
map[curr.second] = t;
worklist.insert(curr);
}
}
}
/// InsertCopies - insert copies into MBB and all of its successors
void StrongPHIElimination::InsertCopies(MachineBasicBlock* MBB,
SmallPtrSet<MachineBasicBlock*, 16>& visited) {
visited.insert(MBB);
std::set<unsigned> pushed;
// Rewrite register uses from Stacks
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
I != E; ++I)
for (unsigned i = 0; i < I->getNumOperands(); ++i)
if (I->getOperand(i).isRegister() &&
Stacks[I->getOperand(i).getReg()].size()) {
I->getOperand(i).setReg(Stacks[I->getOperand(i).getReg()].back());
}
// Schedule the copies for this block
ScheduleCopies(MBB, pushed);
// Recur to our successors
for (GraphTraits<MachineBasicBlock*>::ChildIteratorType I =
GraphTraits<MachineBasicBlock*>::child_begin(MBB), E =
GraphTraits<MachineBasicBlock*>::child_end(MBB); I != E; ++I)
if (!visited.count(*I))
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();
}
/// ComputeUltimateVN - Assuming we are going to join two live intervals,
/// compute what the resultant value numbers for each value in the input two
/// ranges will be. This is complicated by copies between the two which can
/// and will commonly cause multiple value numbers to be merged into one.
///
/// VN is the value number that we're trying to resolve. InstDefiningValue
/// keeps track of the new InstDefiningValue assignment for the result
/// LiveInterval. ThisFromOther/OtherFromThis are sets that keep track of
/// whether a value in this or other is a copy from the opposite set.
/// ThisValNoAssignments/OtherValNoAssignments keep track of value #'s that have
/// already been assigned.
///
/// ThisFromOther[x] - If x is defined as a copy from the other interval, this
/// contains the value number the copy is from.
///
static unsigned ComputeUltimateVN(VNInfo *VNI,
SmallVector<VNInfo*, 16> &NewVNInfo,
DenseMap<VNInfo*, VNInfo*> &ThisFromOther,
DenseMap<VNInfo*, VNInfo*> &OtherFromThis,
SmallVector<int, 16> &ThisValNoAssignments,
SmallVector<int, 16> &OtherValNoAssignments) {
unsigned VN = VNI->id;
// If the VN has already been computed, just return it.
if (ThisValNoAssignments[VN] >= 0)
return ThisValNoAssignments[VN];
// assert(ThisValNoAssignments[VN] != -2 && "Cyclic case?");
// If this val is not a copy from the other val, then it must be a new value
// number in the destination.
DenseMap<VNInfo*, VNInfo*>::iterator I = ThisFromOther.find(VNI);
if (I == ThisFromOther.end()) {
NewVNInfo.push_back(VNI);
return ThisValNoAssignments[VN] = NewVNInfo.size()-1;
}
VNInfo *OtherValNo = I->second;
// Otherwise, this *is* a copy from the RHS. If the other side has already
// been computed, return it.
if (OtherValNoAssignments[OtherValNo->id] >= 0)
return ThisValNoAssignments[VN] = OtherValNoAssignments[OtherValNo->id];
// Mark this value number as currently being computed, then ask what the
// ultimate value # of the other value is.
ThisValNoAssignments[VN] = -2;
unsigned UltimateVN =
ComputeUltimateVN(OtherValNo, NewVNInfo, OtherFromThis, ThisFromOther,
OtherValNoAssignments, ThisValNoAssignments);
return ThisValNoAssignments[VN] = UltimateVN;
}
void StrongPHIElimination::mergeLiveIntervals(unsigned primary,
unsigned secondary,
unsigned secondaryVN) {
LiveIntervals& LI = getAnalysis<LiveIntervals>();
LiveInterval& LHS = LI.getOrCreateInterval(primary);
LiveInterval& RHS = LI.getOrCreateInterval(secondary);
// Compute the final value assignment, assuming that the live ranges can be
// coalesced.
SmallVector<int, 16> LHSValNoAssignments;
SmallVector<int, 16> RHSValNoAssignments;
SmallVector<VNInfo*, 16> NewVNInfo;
LHSValNoAssignments.resize(LHS.getNumValNums(), -1);
RHSValNoAssignments.resize(RHS.getNumValNums(), -1);
NewVNInfo.reserve(LHS.getNumValNums() + RHS.getNumValNums());
for (LiveInterval::vni_iterator I = LHS.vni_begin(), E = LHS.vni_end();
I != E; ++I) {
VNInfo *VNI = *I;
unsigned VN = VNI->id;
if (LHSValNoAssignments[VN] >= 0 || VNI->def == ~1U)
continue;
NewVNInfo.push_back(VNI);
LHSValNoAssignments[VN] = NewVNInfo.size()-1;
}
for (LiveInterval::vni_iterator I = RHS.vni_begin(), E = RHS.vni_end();
I != E; ++I) {
VNInfo *VNI = *I;
unsigned VN = VNI->id;
if (RHSValNoAssignments[VN] >= 0 || VNI->def == ~1U)
continue;
NewVNInfo.push_back(VNI);
RHSValNoAssignments[VN] = NewVNInfo.size()-1;
}
// If we get here, we know that we can coalesce the live ranges. Ask the
// intervals to coalesce themselves now.
LHS.join(RHS, &LHSValNoAssignments[0], &RHSValNoAssignments[0], NewVNInfo);
LI.removeInterval(secondary);
// The valno that was previously the input to the PHI node
// now has a PHIKill.
LHS.getValNumInfo(RHSValNoAssignments[secondaryVN])->hasPHIKill = 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()->getOpcode() == TargetInstrInfo::PHI)
processBlock(I);
// Insert copies
// FIXME: This process should probably preserve LiveVariables
SmallPtrSet<MachineBasicBlock*, 16> visited;
InsertCopies(Fn.begin(), visited);
// Perform renaming
typedef std::map<unsigned, std::map<unsigned, unsigned> > RenameSetType;
for (RenameSetType::iterator I = RenameSets.begin(), E = RenameSets.end();
I != E; ++I)
for (std::map<unsigned, unsigned>::iterator SI = I->second.begin(),
SE = I->second.end(); SI != SE; ++SI) {
mergeLiveIntervals(I->first, SI->first, SI->second);
Fn.getRegInfo().replaceRegWith(SI->first, I->first);
}
// FIXME: Insert last-minute copies
// 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->getOpcode() == TargetInstrInfo::PHI)
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 {
unsigned idx = LI.getDefIndex(LI.getInstructionIndex(PInstr));
PI.removeRange(*PI.getLiveRangeContaining(idx), true);
}
} else {
// If the PHI is not dead, then the valno defined by the PHI
// now has an unknown def.
unsigned idx = LI.getDefIndex(LI.getInstructionIndex(PInstr));
PI.getLiveRangeContaining(idx)->valno->def = ~0U;
}
LI.RemoveMachineInstrFromMaps(PInstr);
PInstr->eraseFromParent();
}
LI.computeNumbering();
return true;
}
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