#define DEBUG_TYPE "phielim"
#include "PHIElimination.h"
-#include "llvm/BasicBlock.h"
-#include "llvm/Instructions.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/Passes.h"
-#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
STATISTIC(NumAtomic, "Number of atomic phis lowered");
STATISTIC(NumSplits, "Number of critical edges split on demand");
-static cl::opt<bool>
-SplitEdges("split-phi-edges",
- cl::desc("Split critical edges during phi elimination"),
- cl::init(false), cl::Hidden);
-
char PHIElimination::ID = 0;
static RegisterPass<PHIElimination>
X("phi-node-elimination", "Eliminate PHI nodes for register allocation");
void llvm::PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreserved<LiveVariables>();
- if (SplitEdges) {
- AU.addRequired<LiveVariables>();
- } else {
- AU.setPreservesCFG();
- AU.addPreservedID(MachineLoopInfoID);
- AU.addPreservedID(MachineDominatorsID);
- }
+ AU.addPreserved<MachineDominatorTree>();
+ // rdar://7401784 This would be nice:
+ // AU.addPreservedID(MachineLoopInfoID);
MachineFunctionPass::getAnalysisUsage(AU);
}
PHIDefs.clear();
PHIKills.clear();
-
bool Changed = false;
// Split critical edges to help the coalescer
- if (SplitEdges)
+ if (LiveVariables *LV = getAnalysisIfAvailable<LiveVariables>())
for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
- Changed |= SplitPHIEdges(Fn, *I);
+ Changed |= SplitPHIEdges(Fn, *I, *LV);
// Populate VRegPHIUseCount
analyzePHINodes(Fn);
return true;
}
-// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg.
-// This needs to be after any def or uses of SrcReg, but before any subsequent
-// point where control flow might jump out of the basic block.
+// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg
+// when following the CFG edge to SuccMBB. This needs to be after any def of
+// SrcReg, but before any subsequent point where control flow might jump out of
+// the basic block.
MachineBasicBlock::iterator
llvm::PHIElimination::FindCopyInsertPoint(MachineBasicBlock &MBB,
+ MachineBasicBlock &SuccMBB,
unsigned SrcReg) {
// Handle the trivial case trivially.
if (MBB.empty())
return MBB.begin();
- // If this basic block does not contain an invoke, then control flow always
- // reaches the end of it, so place the copy there. The logic below works in
- // this case too, but is more expensive.
- if (!isa<InvokeInst>(MBB.getBasicBlock()->getTerminator()))
+ // Usually, we just want to insert the copy before the first terminator
+ // instruction. However, for the edge going to a landing pad, we must insert
+ // the copy before the call/invoke instruction.
+ if (!SuccMBB.isLandingPad())
return MBB.getFirstTerminator();
- // Discover any definition/uses in this basic block.
+ // Discover any defs/uses in this basic block.
SmallPtrSet<MachineInstr*, 8> DefUsesInMBB;
for (MachineRegisterInfo::reg_iterator RI = MRI->reg_begin(SrcReg),
- RE = MRI->reg_end(); RI != RE; ++RI) {
+ RE = MRI->reg_end(); RI != RE; ++RI) {
MachineInstr *DefUseMI = &*RI;
if (DefUseMI->getParent() == &MBB)
DefUsesInMBB.insert(DefUseMI);
MachineBasicBlock::iterator InsertPoint;
if (DefUsesInMBB.empty()) {
- // No def/uses. Insert the copy at the start of the basic block.
+ // No defs. Insert the copy at the start of the basic block.
InsertPoint = MBB.begin();
} else if (DefUsesInMBB.size() == 1) {
- // Insert the copy immediately after the definition/use.
+ // Insert the copy immediately after the def/use.
InsertPoint = *DefUsesInMBB.begin();
++InsertPoint;
} else {
- // Insert the copy immediately after the last definition/use.
+ // Insert the copy immediately after the last def/use.
InsertPoint = MBB.end();
while (!DefUsesInMBB.count(&*--InsertPoint)) {}
++InsertPoint;
// Find a safe location to insert the copy, this may be the first terminator
// in the block (or end()).
- MachineBasicBlock::iterator InsertPos = FindCopyInsertPoint(opBlock, SrcReg);
+ MachineBasicBlock::iterator InsertPos =
+ FindCopyInsertPoint(opBlock, MBB, SrcReg);
// Insert the copy.
TII->copyRegToReg(opBlock, InsertPos, IncomingReg, SrcReg, RC, RC);
// Okay, if we now know that the value is not live out of the block, we can
// add a kill marker in this block saying that it kills the incoming value!
- // When SplitEdges is enabled, the value is never live out.
- if (!ValueIsUsed && !isLiveOut(SrcReg, opBlock, *LV)) {
+ if (!ValueIsUsed && !LV->isLiveOut(SrcReg, opBlock)) {
// In our final twist, we have to decide which instruction kills the
// register. In most cases this is the copy, however, the first
// terminator instruction at the end of the block may also use the value.
// Check that no other terminators use values.
#ifndef NDEBUG
- for (MachineBasicBlock::iterator TI = next(Term); TI != opBlock.end();
- ++TI) {
+ for (MachineBasicBlock::iterator TI = llvm::next(Term);
+ TI != opBlock.end(); ++TI) {
assert(!TI->readsRegister(SrcReg) &&
"Terminator instructions cannot use virtual registers unless"
"they are the first terminator in a block!");
}
bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF,
- MachineBasicBlock &MBB) {
+ MachineBasicBlock &MBB,
+ LiveVariables &LV) {
if (MBB.empty() || MBB.front().getOpcode() != TargetInstrInfo::PHI)
return false; // Quick exit for basic blocks without PHIs.
- LiveVariables &LV = getAnalysis<LiveVariables>();
+
for (MachineBasicBlock::const_iterator BBI = MBB.begin(), BBE = MBB.end();
BBI != BBE && BBI->getOpcode() == TargetInstrInfo::PHI; ++BBI) {
for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2) {
// We break edges when registers are live out from the predecessor block
// (not considering PHI nodes). If the register is live in to this block
// anyway, we would gain nothing from splitting.
- if (isLiveOut(Reg, *PreMBB, LV) && !isLiveIn(Reg, MBB, LV))
+ if (!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB))
SplitCriticalEdge(PreMBB, &MBB);
}
}
return true;
}
-bool llvm::PHIElimination::isLiveOut(unsigned Reg, const MachineBasicBlock &MBB,
- LiveVariables &LV) {
- LiveVariables::VarInfo &VI = LV.getVarInfo(Reg);
-
- // Loop over all of the successors of the basic block, checking to see if
- // the value is either live in the block, or if it is killed in the block.
- std::vector<MachineBasicBlock*> OpSuccBlocks;
- for (MachineBasicBlock::const_succ_iterator SI = MBB.succ_begin(),
- E = MBB.succ_end(); SI != E; ++SI) {
- MachineBasicBlock *SuccMBB = *SI;
-
- // Is it alive in this successor?
- unsigned SuccIdx = SuccMBB->getNumber();
- if (VI.AliveBlocks.test(SuccIdx))
- return true;
- OpSuccBlocks.push_back(SuccMBB);
- }
-
- // Check to see if this value is live because there is a use in a successor
- // that kills it.
- switch (OpSuccBlocks.size()) {
- case 1: {
- MachineBasicBlock *SuccMBB = OpSuccBlocks[0];
- for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i)
- if (VI.Kills[i]->getParent() == SuccMBB)
- return true;
- break;
- }
- case 2: {
- MachineBasicBlock *SuccMBB1 = OpSuccBlocks[0], *SuccMBB2 = OpSuccBlocks[1];
- for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i)
- if (VI.Kills[i]->getParent() == SuccMBB1 ||
- VI.Kills[i]->getParent() == SuccMBB2)
- return true;
- break;
- }
- default:
- std::sort(OpSuccBlocks.begin(), OpSuccBlocks.end());
- for (unsigned i = 0, e = VI.Kills.size(); i != e; ++i)
- if (std::binary_search(OpSuccBlocks.begin(), OpSuccBlocks.end(),
- VI.Kills[i]->getParent()))
- return true;
- }
- return false;
-}
-
-bool llvm::PHIElimination::isLiveIn(unsigned Reg, const MachineBasicBlock &MBB,
- LiveVariables &LV) {
- LiveVariables::VarInfo &VI = LV.getVarInfo(Reg);
-
- return VI.AliveBlocks.test(MBB.getNumber()) || VI.findKill(&MBB);
-}
-
MachineBasicBlock *PHIElimination::SplitCriticalEdge(MachineBasicBlock *A,
MachineBasicBlock *B) {
assert(A && B && "Missing MBB end point");
- ++NumSplits;
- BasicBlock *ABB = const_cast<BasicBlock*>(A->getBasicBlock());
- BasicBlock *BBB = const_cast<BasicBlock*>(B->getBasicBlock());
- assert(ABB && BBB && "End points must have a basic block");
- BasicBlock *BB = BasicBlock::Create(BBB->getContext(),
- ABB->getName() + "." + BBB->getName() +
- "_phi_edge");
- Function *F = ABB->getParent();
- F->getBasicBlockList().insert(F->end(), BB);
+ MachineFunction *MF = A->getParent();
- BranchInst::Create(BBB, BB);
- // We could do more here to produce correct IR, compare
- // llvm::SplitCriticalEdge
+ // We may need to update A's terminator, but we can't do that if AnalyzeBranch
+ // fails. If A uses a jump table, we won't touch it.
+ const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
+ MachineBasicBlock *TBB = 0, *FBB = 0;
+ SmallVector<MachineOperand, 4> Cond;
+ if (TII->AnalyzeBranch(*A, TBB, FBB, Cond))
+ return NULL;
- MachineFunction *MF = A->getParent();
- MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock(BB);
- MF->push_back(NMBB);
+ ++NumSplits;
+
+ MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
+ MF->insert(llvm::next(MachineFunction::iterator(A)), NMBB);
DEBUG(errs() << "PHIElimination splitting critical edge:"
" BB#" << A->getNumber()
<< " -- BB#" << NMBB->getNumber()
<< " -- BB#" << B->getNumber() << '\n');
A->ReplaceUsesOfBlockWith(B, NMBB);
- NMBB->addSuccessor(B);
+ A->updateTerminator();
- // Insert unconditional "jump B" instruction in NMBB.
- SmallVector<MachineOperand, 4> Cond;
- MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, B, NULL, Cond);
-
- if (LiveVariables *LV = getAnalysisIfAvailable<LiveVariables>())
- LV->addNewBlock(NMBB, A);
+ // Insert unconditional "jump B" instruction in NMBB if necessary.
+ NMBB->addSuccessor(B);
+ if (!NMBB->isLayoutSuccessor(B)) {
+ Cond.clear();
+ MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, B, NULL, Cond);
+ }
// Fix PHI nodes in B so they refer to NMBB instead of A
for (MachineBasicBlock::iterator i = B->begin(), e = B->end();
for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
if (i->getOperand(ni+1).getMBB() == A)
i->getOperand(ni+1).setMBB(NMBB);
+
+ if (LiveVariables *LV=getAnalysisIfAvailable<LiveVariables>())
+ LV->addNewBlock(NMBB, A, B);
+
+ if (MachineDominatorTree *MDT=getAnalysisIfAvailable<MachineDominatorTree>())
+ MDT->addNewBlock(NMBB, A);
+
return NMBB;
}
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