-//===- StrongPhiElimination.cpp - Eliminate PHI nodes by inserting copies -===//
+//===- StrongPHIElimination.cpp - Eliminate PHI nodes by inserting copies -===//
//
// The LLVM Compiler Infrastructure
//
-// This file was developed by Owen Anderson and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 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:
+// This pass eliminates PHI instructions by aggressively coalescing the copies
+// that would be inserted by a naive algorithm and only inserting the copies
+// that are necessary. The coalescing technique initially assumes that all
+// registers appearing in a PHI instruction do not interfere. It then eliminates
+// proven interferences, using dominators to only perform a linear number of
+// interference tests instead of the quadratic number of interference tests
+// that this would naively require. This is a technique 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
+//
+// The original implementation constructs a data structure they call a dominance
+// forest for this purpose. The dominance forest was shown to be unnecessary,
+// as it is possible to emulate the creation and traversal of a dominance forest
+// by directly using the dominator tree, rather than actually constructing the
+// dominance forest. This technique is explained in:
+//
+// Boissinot, et al. Revisiting Out-of-SSA Translation for Correctness, Code
+// Quality and Efficiency,
+// In Proceedings of the 7th annual IEEE/ACM International Symposium on Code
+// Generation and Optimization (Seattle, Washington, March 22 - 25, 2009).
+// CGO '09. IEEE, Washington, DC, 114-125.
+//
+// Careful implementation allows for all of the dominator forest interference
+// checks to be performed at once in a single depth-first traversal of the
+// dominator tree, which is what is implemented here.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "strongphielim"
+#include "PHIEliminationUtils.h"
#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/MachineRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
-#include "llvm/Target/TargetMachine.h"
+#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
using namespace llvm;
-
namespace {
- struct VISIBILITY_HIDDEN StrongPHIElimination : public MachineFunctionPass {
+ class StrongPHIElimination : public MachineFunctionPass {
+ public:
static char ID; // Pass identification, replacement for typeid
- StrongPHIElimination() : MachineFunctionPass((intptr_t)&ID) {}
-
- bool runOnMachineFunction(MachineFunction &Fn) {
- computeDFS(Fn);
-
-
- return false;
+ StrongPHIElimination() : MachineFunctionPass(ID) {
+ initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
}
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<MachineDominatorTree>();
- MachineFunctionPass::getAnalysisUsage(AU);
- }
-
- virtual void releaseMemory() {
- preorder.clear();
- maxpreorder.clear();
- }
+ virtual void getAnalysisUsage(AnalysisUsage&) const;
+ bool runOnMachineFunction(MachineFunction&);
private:
- DenseMap<MachineBasicBlock*, unsigned> preorder;
- DenseMap<MachineBasicBlock*, unsigned> maxpreorder;
-
- void computeDFS(MachineFunction& MF);
+ /// This struct represents a single node in the union-find data structure
+ /// representing the variable congruence classes. There is one difference
+ /// from a normal union-find data structure. We steal two bits from the parent
+ /// pointer . One of these bits is used to represent whether the register
+ /// itself has been isolated, and the other is used to represent whether the
+ /// PHI with that register as its destination has been isolated.
+ ///
+ /// Note that this leads to the strange situation where the leader of a
+ /// congruence class may no longer logically be a member, due to being
+ /// isolated.
+ struct Node {
+ enum Flags {
+ kRegisterIsolatedFlag = 1,
+ kPHIIsolatedFlag = 2
+ };
+ Node(unsigned v) : value(v), rank(0) { parent.setPointer(this); }
+
+ Node *getLeader();
+
+ PointerIntPair<Node*, 2> parent;
+ unsigned value;
+ unsigned rank;
+ };
+
+ /// Add a register in a new congruence class containing only itself.
+ void addReg(unsigned);
+
+ /// Join the congruence classes of two registers. This function is biased
+ /// towards the left argument, i.e. after
+ ///
+ /// addReg(r2);
+ /// unionRegs(r1, r2);
+ ///
+ /// the leader of the unioned congruence class is the same as the leader of
+ /// r1's congruence class prior to the union. This is actually relied upon
+ /// in the copy insertion code.
+ void unionRegs(unsigned, unsigned);
+
+ /// Get the color of a register. The color is 0 if the register has been
+ /// isolated.
+ unsigned getRegColor(unsigned);
+
+ // Isolate a register.
+ void isolateReg(unsigned);
+
+ /// Get the color of a PHI. The color of a PHI is 0 if the PHI has been
+ /// isolated. Otherwise, it is the original color of its destination and
+ /// all of its operands (before they were isolated, if they were).
+ unsigned getPHIColor(MachineInstr*);
+
+ /// Isolate a PHI.
+ void isolatePHI(MachineInstr*);
+
+ /// Traverses a basic block, splitting any interferences found between
+ /// registers in the same congruence class. It takes two DenseMaps as
+ /// arguments that it also updates: CurrentDominatingParent, which maps
+ /// a color to the register in that congruence class whose definition was
+ /// most recently seen, and ImmediateDominatingParent, which maps a register
+ /// to the register in the same congruence class that most immediately
+ /// dominates it.
+ ///
+ /// This function assumes that it is being called in a depth-first traversal
+ /// of the dominator tree.
+ void SplitInterferencesForBasicBlock(
+ MachineBasicBlock&,
+ DenseMap<unsigned, unsigned> &CurrentDominatingParent,
+ DenseMap<unsigned, unsigned> &ImmediateDominatingParent);
+
+ // Lowers a PHI instruction, inserting copies of the source and destination
+ // registers as necessary.
+ void InsertCopiesForPHI(MachineInstr*, MachineBasicBlock*);
+
+ // Merges the live interval of Reg into NewReg and renames Reg to NewReg
+ // everywhere that Reg appears. Requires Reg and NewReg to have non-
+ // overlapping lifetimes.
+ void MergeLIsAndRename(unsigned Reg, unsigned NewReg);
+
+ MachineRegisterInfo *MRI;
+ const TargetInstrInfo *TII;
+ MachineDominatorTree *DT;
+ LiveIntervals *LI;
+
+ BumpPtrAllocator Allocator;
+
+ DenseMap<unsigned, Node*> RegNodeMap;
+
+ // Maps a basic block to a list of its defs of registers that appear as PHI
+ // sources.
+ DenseMap<MachineBasicBlock*, std::vector<MachineInstr*> > PHISrcDefs;
+
+ // Maps a color to a pair of a MachineInstr* and a virtual register, which
+ // is the operand of that PHI corresponding to the current basic block.
+ DenseMap<unsigned, std::pair<MachineInstr*, unsigned> > CurrentPHIForColor;
+
+ // FIXME: Can these two data structures be combined? Would a std::multimap
+ // be any better?
+
+ // Stores pairs of predecessor basic blocks and the source registers of
+ // inserted copy instructions.
+ typedef DenseSet<std::pair<MachineBasicBlock*, unsigned> > SrcCopySet;
+ SrcCopySet InsertedSrcCopySet;
+
+ // Maps pairs of predecessor basic blocks and colors to their defining copy
+ // instructions.
+ typedef DenseMap<std::pair<MachineBasicBlock*, unsigned>, MachineInstr*>
+ SrcCopyMap;
+ SrcCopyMap InsertedSrcCopyMap;
+
+ // Maps inserted destination copy registers to their defining copy
+ // instructions.
+ typedef DenseMap<unsigned, MachineInstr*> DestCopyMap;
+ DestCopyMap InsertedDestCopies;
};
- char StrongPHIElimination::ID = 0;
- RegisterPass<StrongPHIElimination> X("strong-phi-node-elimination",
- "Eliminate PHI nodes for register allocation, intelligently");
+ struct MIIndexCompare {
+ MIIndexCompare(LiveIntervals *LiveIntervals) : LI(LiveIntervals) { }
+
+ bool operator()(const MachineInstr *LHS, const MachineInstr *RHS) const {
+ return LI->getInstructionIndex(LHS) < LI->getInstructionIndex(RHS);
+ }
+
+ LiveIntervals *LI;
+ };
+} // namespace
+
+STATISTIC(NumPHIsLowered, "Number of PHIs lowered");
+STATISTIC(NumDestCopiesInserted, "Number of destination copies inserted");
+STATISTIC(NumSrcCopiesInserted, "Number of source copies inserted");
+
+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;
+
+void StrongPHIElimination::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+ AU.addRequired<MachineDominatorTree>();
+ AU.addRequired<SlotIndexes>();
+ AU.addPreserved<SlotIndexes>();
+ AU.addRequired<LiveIntervals>();
+ AU.addPreserved<LiveIntervals>();
+ MachineFunctionPass::getAnalysisUsage(AU);
}
-const PassInfo *llvm::StrongPHIEliminationID = X.getPassInfo();
+static MachineOperand *findLastUse(MachineBasicBlock *MBB, unsigned Reg) {
+ // FIXME: This only needs to check from the first terminator, as only the
+ // first terminator can use a virtual register.
+ for (MachineBasicBlock::reverse_iterator RI = MBB->rbegin(); ; ++RI) {
+ assert (RI != MBB->rend());
+ MachineInstr *MI = &*RI;
-/// 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));
+ for (MachineInstr::mop_iterator OI = MI->operands_begin(),
+ OE = MI->operands_end(); OI != OE; ++OI) {
+ MachineOperand &MO = *OI;
+ if (MO.isReg() && MO.isUse() && MO.getReg() == Reg)
+ return &MO;
}
-
- bool inserted = false;
- for (MachineDomTreeNode::iterator I = node->begin(), E = node->end();
- I != E; ++I)
- if (!frontier.count(*I) && !visited.count(*I)) {
- worklist.push_back(*I);
- inserted = true;
+ }
+}
+
+bool StrongPHIElimination::runOnMachineFunction(MachineFunction &MF) {
+ MRI = &MF.getRegInfo();
+ TII = MF.getTarget().getInstrInfo();
+ DT = &getAnalysis<MachineDominatorTree>();
+ LI = &getAnalysis<LiveIntervals>();
+
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end();
+ I != E; ++I) {
+ for (MachineBasicBlock::iterator BBI = I->begin(), BBE = I->end();
+ BBI != BBE && BBI->isPHI(); ++BBI) {
+ unsigned DestReg = BBI->getOperand(0).getReg();
+ addReg(DestReg);
+ PHISrcDefs[I].push_back(BBI);
+
+ for (unsigned i = 1; i < BBI->getNumOperands(); i += 2) {
+ MachineOperand &SrcMO = BBI->getOperand(i);
+ unsigned SrcReg = SrcMO.getReg();
+ addReg(SrcReg);
+ unionRegs(DestReg, SrcReg);
+
+ MachineInstr *DefMI = MRI->getVRegDef(SrcReg);
+ if (DefMI)
+ PHISrcDefs[DefMI->getParent()].push_back(DefMI);
+ }
+ }
+ }
+
+ // Perform a depth-first traversal of the dominator tree, splitting
+ // interferences amongst PHI-congruence classes.
+ DenseMap<unsigned, unsigned> CurrentDominatingParent;
+ DenseMap<unsigned, unsigned> ImmediateDominatingParent;
+ for (df_iterator<MachineDomTreeNode*> DI = df_begin(DT->getRootNode()),
+ DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
+ SplitInterferencesForBasicBlock(*DI->getBlock(),
+ CurrentDominatingParent,
+ ImmediateDominatingParent);
+ }
+
+ // Insert copies for all PHI source and destination registers.
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end();
+ I != E; ++I) {
+ for (MachineBasicBlock::iterator BBI = I->begin(), BBE = I->end();
+ BBI != BBE && BBI->isPHI(); ++BBI) {
+ InsertCopiesForPHI(BBI, I);
+ }
+ }
+
+ // FIXME: Preserve the equivalence classes during copy insertion and use
+ // the preversed equivalence classes instead of recomputing them.
+ RegNodeMap.clear();
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end();
+ I != E; ++I) {
+ for (MachineBasicBlock::iterator BBI = I->begin(), BBE = I->end();
+ BBI != BBE && BBI->isPHI(); ++BBI) {
+ unsigned DestReg = BBI->getOperand(0).getReg();
+ addReg(DestReg);
+
+ for (unsigned i = 1; i < BBI->getNumOperands(); i += 2) {
+ unsigned SrcReg = BBI->getOperand(i).getReg();
+ addReg(SrcReg);
+ unionRegs(DestReg, SrcReg);
+ }
+ }
+ }
+
+ DenseMap<unsigned, unsigned> RegRenamingMap;
+ bool Changed = false;
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end();
+ I != E; ++I) {
+ MachineBasicBlock::iterator BBI = I->begin(), BBE = I->end();
+ while (BBI != BBE && BBI->isPHI()) {
+ MachineInstr *PHI = BBI;
+
+ assert(PHI->getNumOperands() > 0);
+
+ unsigned SrcReg = PHI->getOperand(1).getReg();
+ unsigned SrcColor = getRegColor(SrcReg);
+ unsigned NewReg = RegRenamingMap[SrcColor];
+ if (!NewReg) {
+ NewReg = SrcReg;
+ RegRenamingMap[SrcColor] = SrcReg;
+ }
+ MergeLIsAndRename(SrcReg, NewReg);
+
+ unsigned DestReg = PHI->getOperand(0).getReg();
+ if (!InsertedDestCopies.count(DestReg))
+ MergeLIsAndRename(DestReg, NewReg);
+
+ for (unsigned i = 3; i < PHI->getNumOperands(); i += 2) {
+ unsigned SrcReg = PHI->getOperand(i).getReg();
+ MergeLIsAndRename(SrcReg, NewReg);
+ }
+
+ ++BBI;
+ LI->RemoveMachineInstrFromMaps(PHI);
+ PHI->eraseFromParent();
+ Changed = true;
+ }
+ }
+
+ // Due to the insertion of copies to split live ranges, the live intervals are
+ // guaranteed to not overlap, except in one case: an original PHI source and a
+ // PHI destination copy. In this case, they have the same value and thus don't
+ // truly intersect, so we merge them into the value live at that point.
+ // FIXME: Is there some better way we can handle this?
+ for (DestCopyMap::iterator I = InsertedDestCopies.begin(),
+ E = InsertedDestCopies.end(); I != E; ++I) {
+ unsigned DestReg = I->first;
+ unsigned DestColor = getRegColor(DestReg);
+ unsigned NewReg = RegRenamingMap[DestColor];
+
+ LiveInterval &DestLI = LI->getInterval(DestReg);
+ LiveInterval &NewLI = LI->getInterval(NewReg);
+
+ assert(DestLI.ranges.size() == 1
+ && "PHI destination copy's live interval should be a single live "
+ "range from the beginning of the BB to the copy instruction.");
+ LiveRange *DestLR = DestLI.begin();
+ VNInfo *NewVNI = NewLI.getVNInfoAt(DestLR->start);
+ if (!NewVNI) {
+ NewVNI = NewLI.createValueCopy(DestLR->valno, LI->getVNInfoAllocator());
+ MachineInstr *CopyInstr = I->second;
+ CopyInstr->getOperand(1).setIsKill(true);
+ }
+
+ LiveRange NewLR(DestLR->start, DestLR->end, NewVNI);
+ NewLI.addRange(NewLR);
+
+ LI->removeInterval(DestReg);
+ MRI->replaceRegWith(DestReg, NewReg);
+ }
+
+ // Adjust the live intervals of all PHI source registers to handle the case
+ // where the PHIs in successor blocks were the only later uses of the source
+ // register.
+ for (SrcCopySet::iterator I = InsertedSrcCopySet.begin(),
+ E = InsertedSrcCopySet.end(); I != E; ++I) {
+ MachineBasicBlock *MBB = I->first;
+ unsigned SrcReg = I->second;
+ if (unsigned RenamedRegister = RegRenamingMap[getRegColor(SrcReg)])
+ SrcReg = RenamedRegister;
+
+ LiveInterval &SrcLI = LI->getInterval(SrcReg);
+
+ bool isLiveOut = false;
+ for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
+ SE = MBB->succ_end(); SI != SE; ++SI) {
+ if (SrcLI.liveAt(LI->getMBBStartIdx(*SI))) {
+ isLiveOut = true;
break;
}
-
- if (!inserted) {
- frontier.erase(currNode);
- visited.insert(currNode);
- maxpreorder.insert(std::make_pair(currNode->getBlock(), time));
-
- worklist.pop_back();
+ }
+
+ if (isLiveOut)
+ continue;
+
+ MachineOperand *LastUse = findLastUse(MBB, SrcReg);
+ assert(LastUse);
+ SlotIndex LastUseIndex = LI->getInstructionIndex(LastUse->getParent());
+ SrcLI.removeRange(LastUseIndex.getRegSlot(), LI->getMBBEndIdx(MBB));
+ LastUse->setIsKill(true);
+ }
+
+ Allocator.Reset();
+ RegNodeMap.clear();
+ PHISrcDefs.clear();
+ InsertedSrcCopySet.clear();
+ InsertedSrcCopyMap.clear();
+ InsertedDestCopies.clear();
+
+ return Changed;
+}
+
+void StrongPHIElimination::addReg(unsigned Reg) {
+ if (RegNodeMap.count(Reg))
+ return;
+ RegNodeMap[Reg] = new (Allocator) Node(Reg);
+}
+
+StrongPHIElimination::Node*
+StrongPHIElimination::Node::getLeader() {
+ Node *N = this;
+ Node *Parent = parent.getPointer();
+ Node *Grandparent = Parent->parent.getPointer();
+
+ while (Parent != Grandparent) {
+ N->parent.setPointer(Grandparent);
+ N = Grandparent;
+ Parent = Parent->parent.getPointer();
+ Grandparent = Parent->parent.getPointer();
+ }
+
+ return Parent;
+}
+
+unsigned StrongPHIElimination::getRegColor(unsigned Reg) {
+ DenseMap<unsigned, Node*>::iterator RI = RegNodeMap.find(Reg);
+ if (RI == RegNodeMap.end())
+ return 0;
+ Node *Node = RI->second;
+ if (Node->parent.getInt() & Node::kRegisterIsolatedFlag)
+ return 0;
+ return Node->getLeader()->value;
+}
+
+void StrongPHIElimination::unionRegs(unsigned Reg1, unsigned Reg2) {
+ Node *Node1 = RegNodeMap[Reg1]->getLeader();
+ Node *Node2 = RegNodeMap[Reg2]->getLeader();
+
+ if (Node1->rank > Node2->rank) {
+ Node2->parent.setPointer(Node1->getLeader());
+ } else if (Node1->rank < Node2->rank) {
+ Node1->parent.setPointer(Node2->getLeader());
+ } else if (Node1 != Node2) {
+ Node2->parent.setPointer(Node1->getLeader());
+ Node1->rank++;
+ }
+}
+
+void StrongPHIElimination::isolateReg(unsigned Reg) {
+ Node *Node = RegNodeMap[Reg];
+ Node->parent.setInt(Node->parent.getInt() | Node::kRegisterIsolatedFlag);
+}
+
+unsigned StrongPHIElimination::getPHIColor(MachineInstr *PHI) {
+ assert(PHI->isPHI());
+
+ unsigned DestReg = PHI->getOperand(0).getReg();
+ Node *DestNode = RegNodeMap[DestReg];
+ if (DestNode->parent.getInt() & Node::kPHIIsolatedFlag)
+ return 0;
+
+ for (unsigned i = 1; i < PHI->getNumOperands(); i += 2) {
+ unsigned SrcColor = getRegColor(PHI->getOperand(i).getReg());
+ if (SrcColor)
+ return SrcColor;
+ }
+ return 0;
+}
+
+void StrongPHIElimination::isolatePHI(MachineInstr *PHI) {
+ assert(PHI->isPHI());
+ Node *Node = RegNodeMap[PHI->getOperand(0).getReg()];
+ Node->parent.setInt(Node->parent.getInt() | Node::kPHIIsolatedFlag);
+}
+
+/// SplitInterferencesForBasicBlock - traverses a basic block, splitting any
+/// interferences found between registers in the same congruence class. It
+/// takes two DenseMaps as arguments that it also updates:
+///
+/// 1) CurrentDominatingParent, which maps a color to the register in that
+/// congruence class whose definition was most recently seen.
+///
+/// 2) ImmediateDominatingParent, which maps a register to the register in the
+/// same congruence class that most immediately dominates it.
+///
+/// This function assumes that it is being called in a depth-first traversal
+/// of the dominator tree.
+///
+/// The algorithm used here is a generalization of the dominance-based SSA test
+/// for two variables. If there are variables a_1, ..., a_n such that
+///
+/// def(a_1) dom ... dom def(a_n),
+///
+/// then we can test for an interference between any two a_i by only using O(n)
+/// interference tests between pairs of variables. If i < j and a_i and a_j
+/// interfere, then a_i is alive at def(a_j), so it is also alive at def(a_i+1).
+/// Thus, in order to test for an interference involving a_i, we need only check
+/// for a potential interference with a_i+1.
+///
+/// This method can be generalized to arbitrary sets of variables by performing
+/// a depth-first traversal of the dominator tree. As we traverse down a branch
+/// of the dominator tree, we keep track of the current dominating variable and
+/// only perform an interference test with that variable. However, when we go to
+/// another branch of the dominator tree, the definition of the current dominating
+/// variable may no longer dominate the current block. In order to correct this,
+/// we need to use a stack of past choices of the current dominating variable
+/// and pop from this stack until we find a variable whose definition actually
+/// dominates the current block.
+///
+/// There will be one push on this stack for each variable that has become the
+/// current dominating variable, so instead of using an explicit stack we can
+/// simply associate the previous choice for a current dominating variable with
+/// the new choice. This works better in our implementation, where we test for
+/// interference in multiple distinct sets at once.
+void
+StrongPHIElimination::SplitInterferencesForBasicBlock(
+ MachineBasicBlock &MBB,
+ DenseMap<unsigned, unsigned> &CurrentDominatingParent,
+ DenseMap<unsigned, unsigned> &ImmediateDominatingParent) {
+ // Sort defs by their order in the original basic block, as the code below
+ // assumes that it is processing definitions in dominance order.
+ std::vector<MachineInstr*> &DefInstrs = PHISrcDefs[&MBB];
+ std::sort(DefInstrs.begin(), DefInstrs.end(), MIIndexCompare(LI));
+
+ for (std::vector<MachineInstr*>::const_iterator BBI = DefInstrs.begin(),
+ BBE = DefInstrs.end(); BBI != BBE; ++BBI) {
+ for (MachineInstr::const_mop_iterator I = (*BBI)->operands_begin(),
+ E = (*BBI)->operands_end(); I != E; ++I) {
+ const MachineOperand &MO = *I;
+
+ // FIXME: This would be faster if it were possible to bail out of checking
+ // an instruction's operands after the explicit defs, but this is incorrect
+ // for variadic instructions, which may appear before register allocation
+ // in the future.
+ if (!MO.isReg() || !MO.isDef())
+ continue;
+
+ unsigned DestReg = MO.getReg();
+ if (!DestReg || !TargetRegisterInfo::isVirtualRegister(DestReg))
+ continue;
+
+ // If the virtual register being defined is not used in any PHI or has
+ // already been isolated, then there are no more interferences to check.
+ unsigned DestColor = getRegColor(DestReg);
+ if (!DestColor)
+ continue;
+
+ // The input to this pass sometimes is not in SSA form in every basic
+ // block, as some virtual registers have redefinitions. We could eliminate
+ // this by fixing the passes that generate the non-SSA code, or we could
+ // handle it here by tracking defining machine instructions rather than
+ // virtual registers. For now, we just handle the situation conservatively
+ // in a way that will possibly lead to false interferences.
+ unsigned &CurrentParent = CurrentDominatingParent[DestColor];
+ unsigned NewParent = CurrentParent;
+ if (NewParent == DestReg)
+ continue;
+
+ // Pop registers from the stack represented by ImmediateDominatingParent
+ // until we find a parent that dominates the current instruction.
+ while (NewParent && (!DT->dominates(MRI->getVRegDef(NewParent), *BBI)
+ || !getRegColor(NewParent)))
+ NewParent = ImmediateDominatingParent[NewParent];
+
+ // If NewParent is nonzero, then its definition dominates the current
+ // instruction, so it is only necessary to check for the liveness of
+ // NewParent in order to check for an interference.
+ if (NewParent
+ && LI->getInterval(NewParent).liveAt(LI->getInstructionIndex(*BBI))) {
+ // If there is an interference, always isolate the new register. This
+ // could be improved by using a heuristic that decides which of the two
+ // registers to isolate.
+ isolateReg(DestReg);
+ CurrentParent = NewParent;
+ } else {
+ // If there is no interference, update ImmediateDominatingParent and set
+ // the CurrentDominatingParent for this color to the current register.
+ ImmediateDominatingParent[DestReg] = NewParent;
+ CurrentParent = DestReg;
+ }
}
}
-}
\ No newline at end of file
+
+ // We now walk the PHIs in successor blocks and check for interferences. This
+ // is necessary because the use of a PHI's operands are logically contained in
+ // the predecessor block. The def of a PHI's destination register is processed
+ // along with the other defs in a basic block.
+
+ CurrentPHIForColor.clear();
+
+ for (MachineBasicBlock::succ_iterator SI = MBB.succ_begin(),
+ SE = MBB.succ_end(); SI != SE; ++SI) {
+ for (MachineBasicBlock::iterator BBI = (*SI)->begin(), BBE = (*SI)->end();
+ BBI != BBE && BBI->isPHI(); ++BBI) {
+ MachineInstr *PHI = BBI;
+
+ // If a PHI is already isolated, either by being isolated directly or
+ // having all of its operands isolated, ignore it.
+ unsigned Color = getPHIColor(PHI);
+ if (!Color)
+ continue;
+
+ // Find the index of the PHI operand that corresponds to this basic block.
+ unsigned PredIndex;
+ for (PredIndex = 1; PredIndex < PHI->getNumOperands(); PredIndex += 2) {
+ if (PHI->getOperand(PredIndex + 1).getMBB() == &MBB)
+ break;
+ }
+ assert(PredIndex < PHI->getNumOperands());
+ unsigned PredOperandReg = PHI->getOperand(PredIndex).getReg();
+
+ // Pop registers from the stack represented by ImmediateDominatingParent
+ // until we find a parent that dominates the current instruction.
+ unsigned &CurrentParent = CurrentDominatingParent[Color];
+ unsigned NewParent = CurrentParent;
+ while (NewParent
+ && (!DT->dominates(MRI->getVRegDef(NewParent)->getParent(), &MBB)
+ || !getRegColor(NewParent)))
+ NewParent = ImmediateDominatingParent[NewParent];
+ CurrentParent = NewParent;
+
+ // If there is an interference with a register, always isolate the
+ // register rather than the PHI. It is also possible to isolate the
+ // PHI, but that introduces copies for all of the registers involved
+ // in that PHI.
+ if (NewParent && LI->isLiveOutOfMBB(LI->getInterval(NewParent), &MBB)
+ && NewParent != PredOperandReg)
+ isolateReg(NewParent);
+
+ std::pair<MachineInstr*, unsigned>
+ &CurrentPHI = CurrentPHIForColor[Color];
+
+ // If two PHIs have the same operand from every shared predecessor, then
+ // they don't actually interfere. Otherwise, isolate the current PHI. This
+ // could possibly be improved, e.g. we could isolate the PHI with the
+ // fewest operands.
+ if (CurrentPHI.first && CurrentPHI.second != PredOperandReg)
+ isolatePHI(PHI);
+ else
+ CurrentPHI = std::make_pair(PHI, PredOperandReg);
+ }
+ }
+}
+
+void StrongPHIElimination::InsertCopiesForPHI(MachineInstr *PHI,
+ MachineBasicBlock *MBB) {
+ assert(PHI->isPHI());
+ ++NumPHIsLowered;
+ unsigned PHIColor = getPHIColor(PHI);
+
+ for (unsigned i = 1; i < PHI->getNumOperands(); i += 2) {
+ MachineOperand &SrcMO = PHI->getOperand(i);
+
+ // If a source is defined by an implicit def, there is no need to insert a
+ // copy in the predecessor.
+ if (SrcMO.isUndef())
+ continue;
+
+ unsigned SrcReg = SrcMO.getReg();
+ assert(TargetRegisterInfo::isVirtualRegister(SrcReg) &&
+ "Machine PHI Operands must all be virtual registers!");
+
+ MachineBasicBlock *PredBB = PHI->getOperand(i + 1).getMBB();
+ unsigned SrcColor = getRegColor(SrcReg);
+
+ // If neither the PHI nor the operand were isolated, then we only need to
+ // set the phi-kill flag on the VNInfo at this PHI.
+ if (PHIColor && SrcColor == PHIColor) {
+ LiveInterval &SrcInterval = LI->getInterval(SrcReg);
+ SlotIndex PredIndex = LI->getMBBEndIdx(PredBB);
+ VNInfo *SrcVNI = SrcInterval.getVNInfoBefore(PredIndex);
+ assert(SrcVNI);
+ SrcVNI->setHasPHIKill(true);
+ continue;
+ }
+
+ unsigned CopyReg = 0;
+ if (PHIColor) {
+ SrcCopyMap::const_iterator I
+ = InsertedSrcCopyMap.find(std::make_pair(PredBB, PHIColor));
+ CopyReg
+ = I != InsertedSrcCopyMap.end() ? I->second->getOperand(0).getReg() : 0;
+ }
+
+ if (!CopyReg) {
+ const TargetRegisterClass *RC = MRI->getRegClass(SrcReg);
+ CopyReg = MRI->createVirtualRegister(RC);
+
+ MachineBasicBlock::iterator
+ CopyInsertPoint = findPHICopyInsertPoint(PredBB, MBB, SrcReg);
+ unsigned SrcSubReg = SrcMO.getSubReg();
+ MachineInstr *CopyInstr = BuildMI(*PredBB,
+ CopyInsertPoint,
+ PHI->getDebugLoc(),
+ TII->get(TargetOpcode::COPY),
+ CopyReg).addReg(SrcReg, 0, SrcSubReg);
+ LI->InsertMachineInstrInMaps(CopyInstr);
+ ++NumSrcCopiesInserted;
+
+ // addLiveRangeToEndOfBlock() also adds the phikill flag to the VNInfo for
+ // the newly added range.
+ LI->addLiveRangeToEndOfBlock(CopyReg, CopyInstr);
+ InsertedSrcCopySet.insert(std::make_pair(PredBB, SrcReg));
+
+ addReg(CopyReg);
+ if (PHIColor) {
+ unionRegs(PHIColor, CopyReg);
+ assert(getRegColor(CopyReg) != CopyReg);
+ } else {
+ PHIColor = CopyReg;
+ assert(getRegColor(CopyReg) == CopyReg);
+ }
+
+ if (!InsertedSrcCopyMap.count(std::make_pair(PredBB, PHIColor)))
+ InsertedSrcCopyMap[std::make_pair(PredBB, PHIColor)] = CopyInstr;
+ }
+
+ SrcMO.setReg(CopyReg);
+
+ // If SrcReg is not live beyond the PHI, trim its interval so that it is no
+ // longer live-in to MBB. Note that SrcReg may appear in other PHIs that are
+ // processed later, but this is still correct to do at this point because we
+ // never rely on LiveIntervals being correct while inserting copies.
+ // FIXME: Should this just count uses at PHIs like the normal PHIElimination
+ // pass does?
+ LiveInterval &SrcLI = LI->getInterval(SrcReg);
+ SlotIndex MBBStartIndex = LI->getMBBStartIdx(MBB);
+ SlotIndex PHIIndex = LI->getInstructionIndex(PHI);
+ SlotIndex NextInstrIndex = PHIIndex.getNextIndex();
+ if (SrcLI.liveAt(MBBStartIndex) && SrcLI.expiredAt(NextInstrIndex))
+ SrcLI.removeRange(MBBStartIndex, PHIIndex, true);
+ }
+
+ unsigned DestReg = PHI->getOperand(0).getReg();
+ unsigned DestColor = getRegColor(DestReg);
+
+ if (PHIColor && DestColor == PHIColor) {
+ LiveInterval &DestLI = LI->getInterval(DestReg);
+
+ // Set the phi-def flag for the VN at this PHI.
+ SlotIndex PHIIndex = LI->getInstructionIndex(PHI);
+ VNInfo *DestVNI = DestLI.getVNInfoAt(PHIIndex.getRegSlot());
+ assert(DestVNI);
+ DestVNI->setIsPHIDef(true);
+
+ // Prior to PHI elimination, the live ranges of PHIs begin at their defining
+ // instruction. After PHI elimination, PHI instructions are replaced by VNs
+ // with the phi-def flag set, and the live ranges of these VNs start at the
+ // beginning of the basic block.
+ SlotIndex MBBStartIndex = LI->getMBBStartIdx(MBB);
+ DestVNI->def = MBBStartIndex;
+ DestLI.addRange(LiveRange(MBBStartIndex,
+ PHIIndex.getRegSlot(),
+ DestVNI));
+ return;
+ }
+
+ const TargetRegisterClass *RC = MRI->getRegClass(DestReg);
+ unsigned CopyReg = MRI->createVirtualRegister(RC);
+
+ MachineInstr *CopyInstr = BuildMI(*MBB,
+ MBB->SkipPHIsAndLabels(MBB->begin()),
+ PHI->getDebugLoc(),
+ TII->get(TargetOpcode::COPY),
+ DestReg).addReg(CopyReg);
+ LI->InsertMachineInstrInMaps(CopyInstr);
+ PHI->getOperand(0).setReg(CopyReg);
+ ++NumDestCopiesInserted;
+
+ // Add the region from the beginning of MBB to the copy instruction to
+ // CopyReg's live interval, and give the VNInfo the phidef flag.
+ LiveInterval &CopyLI = LI->getOrCreateInterval(CopyReg);
+ SlotIndex MBBStartIndex = LI->getMBBStartIdx(MBB);
+ SlotIndex DestCopyIndex = LI->getInstructionIndex(CopyInstr);
+ VNInfo *CopyVNI = CopyLI.getNextValue(MBBStartIndex,
+ LI->getVNInfoAllocator());
+ CopyVNI->setIsPHIDef(true);
+ CopyLI.addRange(LiveRange(MBBStartIndex,
+ DestCopyIndex.getRegSlot(),
+ CopyVNI));
+
+ // Adjust DestReg's live interval to adjust for its new definition at
+ // CopyInstr.
+ LiveInterval &DestLI = LI->getOrCreateInterval(DestReg);
+ SlotIndex PHIIndex = LI->getInstructionIndex(PHI);
+ DestLI.removeRange(PHIIndex.getRegSlot(), DestCopyIndex.getRegSlot());
+
+ VNInfo *DestVNI = DestLI.getVNInfoAt(DestCopyIndex.getRegSlot());
+ assert(DestVNI);
+ DestVNI->def = DestCopyIndex.getRegSlot();
+
+ InsertedDestCopies[CopyReg] = CopyInstr;
+}
+
+void StrongPHIElimination::MergeLIsAndRename(unsigned Reg, unsigned NewReg) {
+ if (Reg == NewReg)
+ return;
+
+ LiveInterval &OldLI = LI->getInterval(Reg);
+ LiveInterval &NewLI = LI->getInterval(NewReg);
+
+ // Merge the live ranges of the two registers.
+ DenseMap<VNInfo*, VNInfo*> VNMap;
+ for (LiveInterval::iterator LRI = OldLI.begin(), LRE = OldLI.end();
+ LRI != LRE; ++LRI) {
+ LiveRange OldLR = *LRI;
+ VNInfo *OldVN = OldLR.valno;
+
+ VNInfo *&NewVN = VNMap[OldVN];
+ if (!NewVN) {
+ NewVN = NewLI.createValueCopy(OldVN, LI->getVNInfoAllocator());
+ VNMap[OldVN] = NewVN;
+ }
+
+ LiveRange LR(OldLR.start, OldLR.end, NewVN);
+ NewLI.addRange(LR);
+ }
+
+ // Remove the LiveInterval for the register being renamed and replace all
+ // of its defs and uses with the new register.
+ LI->removeInterval(Reg);
+ MRI->replaceRegWith(Reg, NewReg);
+}
projects / oota-llvm.git / blobdiff