-//===- StrongPhiElimination.cpp - Eliminate PHI nodes by inserting copies -===//
+//===- StrongPHIElimination.cpp - Eliminate PHI nodes by inserting copies -===//
//
// The LLVM Compiler Infrastructure
//
//
//===----------------------------------------------------------------------===//
//
-// 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/MachineLoopInfo.h"
+#include "llvm/CodeGen/MachineInstrBuilder.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/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) {}
-
- // 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 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.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();
+ StrongPHIElimination() : MachineFunctionPass(ID) {
+ initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
}
+ virtual void getAnalysisUsage(AnalysisUsage&) const;
+ bool runOnMachineFunction(MachineFunction&);
+
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(); }
+ /// 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;
};
-
- 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(MachineBasicBlock* MBB,
- SmallPtrSet<MachineBasicBlock*, 16>& v);
- void mergeLiveIntervals(unsigned primary, unsigned secondary,
- MachineBasicBlock* pred);
+
+ /// 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;
-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));
+ struct MIIndexCompare {
+ MIIndexCompare(LiveIntervals *LiveIntervals) : LI(LiveIntervals) { }
+
+ bool operator()(const MachineInstr *LHS, const MachineInstr *RHS) const {
+ return LI->getInstructionIndex(LHS) < LI->getInstructionIndex(RHS);
}
-
- 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();
+
+ 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);
+}
+
+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;
+
+ 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;
}
}
}
-namespace {
+bool StrongPHIElimination::runOnMachineFunction(MachineFunction &MF) {
+ MRI = &MF.getRegInfo();
+ TII = MF.getTarget().getInstrInfo();
+ DT = &getAnalysis<MachineDominatorTree>();
+ LI = &getAnalysis<LiveIntervals>();
-/// 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;
+ 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);
+ }
-/// 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();
+ // Insert copies for all PHI source and destination registers.
+ for (MachineFunction::iterator I = MF.begin(), E = MF.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;
+ for (MachineBasicBlock::iterator BBI = I->begin(), BBE = I->end();
+ BBI != BBE && BBI->isPHI(); ++BBI) {
+ InsertCopiesForPHI(BBI, I);
}
-
- // 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);
-}
+ // 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);
-/// 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;
+ for (unsigned i = 1; i < BBI->getNumOperands(); i += 2) {
+ unsigned SrcReg = BBI->getOperand(i).getReg();
+ addReg(SrcReg);
+ unionRegs(DestReg, SrcReg);
+ }
+ }
}
-
- 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;
+ 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;
}
- // 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;
+ 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;
}
}
-
- 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;
- }
+ // 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& 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, 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();
-
- // 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
- PHIUnion.insert(std::make_pair(SrcReg,P->getOperand(i).getMBB()));
- UnionedBlocks.insert(MRI.getVRegDef(SrcReg)->getParent());
- }
+ 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);
}
-
- // 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);
- }
- }
+
+ 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;
}
}
-
- // 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, MachineBasicBlock*>::iterator I = PHIUnion.begin(),
- E = PHIUnion.end(); I != E; ++I)
- ProcessedNames.insert(I->first);
-
- ++P;
+
+ 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;
}
-/// 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();
+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);
}
-/// ScheduleCopies - Insert copies into predecessor blocks, scheduling
-/// them properly so as to avoid the 'lost copy' and the 'virtual swap'
-/// problems.
+/// 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:
///
-/// 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::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;
+/// 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;
+ }
}
}
-
- 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::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;
-
- // 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::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);
-
+
+ // 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;
- } 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);
+ }
+ 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);
}
}
-
- // Renumber the instructions so that we can perform the index computations
- // needed to create new live intervals.
- LI.computeNumbering();
-
- // 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.count(I->first))
- LI.addLiveRangeToEndOfBlock(I->first, I->second);
}
-/// 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();
-}
+void StrongPHIElimination::InsertCopiesForPHI(MachineInstr *PHI,
+ MachineBasicBlock *MBB) {
+ assert(PHI->isPHI());
+ ++NumPHIsLowered;
+ unsigned PHIColor = getPHIColor(PHI);
-void StrongPHIElimination::mergeLiveIntervals(unsigned primary,
- unsigned secondary,
- MachineBasicBlock* pred) {
-
- LiveIntervals& LI = getAnalysis<LiveIntervals>();
- LiveInterval& LHS = LI.getOrCreateInterval(primary);
- LiveInterval& RHS = LI.getOrCreateInterval(secondary);
-
- LI.computeNumbering();
-
- const LiveRange* RangeMergingIn =
- RHS.getLiveRangeContaining(LI.getMBBEndIdx(pred));
- VNInfo* NewVN = LHS.getNextValue(RangeMergingIn->valno->def,
- RangeMergingIn->valno->copy,
- LI.getVNInfoAllocator());
- NewVN->hasPHIKill = true;
- LiveRange NewRange(RangeMergingIn->start, RangeMergingIn->end, NewVN);
- RHS.removeRange(RangeMergingIn->start, RangeMergingIn->end, true);
- LHS.addRange(NewRange);
-}
+ for (unsigned i = 1; i < PHI->getNumOperands(); i += 2) {
+ MachineOperand &SrcMO = PHI->getOperand(i);
-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 LiveIntervals
- SmallPtrSet<MachineBasicBlock*, 16> visited;
- InsertCopies(Fn.begin(), visited);
-
- // Perform renaming
- 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 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);
+ // 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;
}
-
- // 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);
+
+ 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 {
- unsigned idx = LI.getDefIndex(LI.getInstructionIndex(PInstr));
- PI.removeRange(*PI.getLiveRangeContaining(idx), true);
+ PHIColor = CopyReg;
+ assert(getRegColor(CopyReg) == CopyReg);
}
- } 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;
+
+ if (!InsertedSrcCopyMap.count(std::make_pair(PredBB, PHIColor)))
+ InsertedSrcCopyMap[std::make_pair(PredBB, PHIColor)] = CopyInstr;
}
-
- LI.RemoveMachineInstrFromMaps(PInstr);
- PInstr->eraseFromParent();
+
+ 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);
}
-
- LI.computeNumbering();
-
- return 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