#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
-#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/Function.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/ADT/SmallPtrSet.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(true), cl::Hidden);
-
char PHIElimination::ID = 0;
static RegisterPass<PHIElimination>
X("phi-node-elimination", "Eliminate PHI nodes for register allocation");
const PassInfo *const llvm::PHIEliminationID = &X;
-namespace llvm { FunctionPass *createLocalRegisterAllocator(); }
-
-// Should we run edge splitting?
-static bool shouldSplitEdges() {
- // Edge splitting breaks the local register allocator. It cannot tolerate
- // LiveVariables being run.
- if (RegisterRegAlloc::getDefault() == createLocalRegisterAllocator)
- return false;
- return SplitEdges;
-}
-
void llvm::PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreserved<LiveVariables>();
AU.addPreserved<MachineDominatorTree>();
- if (shouldSplitEdges()) {
- AU.addRequired<LiveVariables>();
- } else {
- AU.setPreservesCFG();
- AU.addPreservedID(MachineLoopInfoID);
- }
+ // rdar://7401784 This would be nice:
+ // AU.addPreservedID(MachineLoopInfoID);
MachineFunctionPass::getAnalysisUsage(AU);
}
bool Changed = false;
// Split critical edges to help the coalescer
- if (shouldSplitEdges())
+ 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);
// 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!
- 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);
-
- if (VI.AliveBlocks.test(MBB.getNumber()))
- return true;
-
- // defined in MBB?
- const MachineInstr *Def = MRI->getVRegDef(Reg);
- if (Def && Def->getParent() == &MBB)
- return false;
-
- // killed in MBB?
- return VI.findKill(&MBB);
-}
-
MachineBasicBlock *PHIElimination::SplitCriticalEdge(MachineBasicBlock *A,
MachineBasicBlock *B) {
assert(A && B && "Missing MBB end point");
- ++NumSplits;
MachineFunction *MF = A->getParent();
+
+ // 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;
+
+ ++NumSplits;
+
MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
- MF->push_back(NMBB);
+ 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);
- // If A may fall through to B, we may have to insert a branch.
- if (A->isLayoutSuccessor(B))
- A->updateTerminator();
+ A->updateTerminator();
- // Insert unconditional "jump B" instruction in NMBB.
+ // Insert unconditional "jump B" instruction in NMBB if necessary.
NMBB->addSuccessor(B);
- SmallVector<MachineOperand, 4> Cond;
- MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, B, NULL, Cond);
+ 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();
i->getOperand(ni+1).setMBB(NMBB);
if (LiveVariables *LV=getAnalysisIfAvailable<LiveVariables>())
- LV->addNewBlock(NMBB, A);
+ LV->addNewBlock(NMBB, A, B);
if (MachineDominatorTree *MDT=getAnalysisIfAvailable<MachineDominatorTree>())
MDT->addNewBlock(NMBB, A);
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