X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FMachineSink.cpp;h=bc383cba455c79e09175eade07e3ff0ae3cdec73;hb=1e94e98b0ec44c5b04eaa8c9e7fb6d7669b3cdea;hp=b9c1eb4b684fe9d7493c35ce244fb614ae0f7497;hpb=b0cdf8a4466d02c66c84b6b30953709fa9225a30;p=oota-llvm.git diff --git a/lib/CodeGen/MachineSink.cpp b/lib/CodeGen/MachineSink.cpp index b9c1eb4b684..bc383cba455 100644 --- a/lib/CodeGen/MachineSink.cpp +++ b/lib/CodeGen/MachineSink.cpp @@ -32,7 +32,7 @@ #include "llvm/Support/raw_ostream.h" using namespace llvm; -static cl::opt +static cl::opt SplitEdges("machine-sink-split", cl::desc("Split critical edges during machine sinking"), cl::init(true), cl::Hidden); @@ -57,7 +57,9 @@ namespace { public: static char ID; // Pass identification - MachineSinking() : MachineFunctionPass(ID) {} + MachineSinking() : MachineFunctionPass(ID) { + initializeMachineSinkingPass(*PassRegistry::getPassRegistry()); + } virtual bool runOnMachineFunction(MachineFunction &MF); @@ -88,16 +90,36 @@ namespace { bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB, MachineBasicBlock *DefMBB, bool &BreakPHIEdge, bool &LocalUse) const; + MachineBasicBlock *FindSuccToSinkTo(MachineInstr *MI, MachineBasicBlock *MBB, + bool &BreakPHIEdge); + bool isProfitableToSinkTo(unsigned Reg, MachineInstr *MI, + MachineBasicBlock *MBB, + MachineBasicBlock *SuccToSinkTo); + bool PerformTrivialForwardCoalescing(MachineInstr *MI, MachineBasicBlock *MBB); }; + + // SuccessorSorter - Sort Successors according to their loop depth. + struct SuccessorSorter { + SuccessorSorter(MachineLoopInfo *LoopInfo) : LI(LoopInfo) {} + bool operator()(const MachineBasicBlock *LHS, + const MachineBasicBlock *RHS) const { + return LI->getLoopDepth(LHS) < LI->getLoopDepth(RHS); + } + MachineLoopInfo *LI; + }; } // end anonymous namespace char MachineSinking::ID = 0; -INITIALIZE_PASS(MachineSinking, "machine-sink", - "Machine code sinking", false, false); - -FunctionPass *llvm::createMachineSinkingPass() { return new MachineSinking(); } +char &llvm::MachineSinkingID = MachineSinking::ID; +INITIALIZE_PASS_BEGIN(MachineSinking, "machine-sink", + "Machine code sinking", false, false) +INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) +INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo) +INITIALIZE_AG_DEPENDENCY(AliasAnalysis) +INITIALIZE_PASS_END(MachineSinking, "machine-sink", + "Machine code sinking", false, false) bool MachineSinking::PerformTrivialForwardCoalescing(MachineInstr *MI, MachineBasicBlock *MBB) { @@ -140,14 +162,10 @@ MachineSinking::AllUsesDominatedByBlock(unsigned Reg, assert(TargetRegisterInfo::isVirtualRegister(Reg) && "Only makes sense for vregs"); + // Ignore debug uses because debug info doesn't affect the code. if (MRI->use_nodbg_empty(Reg)) return true; - // Ignoring debug uses is necessary so debug info doesn't affect the code. - // This may leave a referencing dbg_value in the original block, before - // the definition of the vreg. Dwarf generator handles this although the - // user might not get the right info at runtime. - // BreakPHIEdge is true if all the uses are in the successor MBB being sunken // into and they are all PHI nodes. In this case, machine-sink must break // the critical edge first. e.g. @@ -258,8 +276,11 @@ bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) { if (MI->isDebugValue()) continue; - if (PerformTrivialForwardCoalescing(MI, &MBB)) + bool Joined = PerformTrivialForwardCoalescing(MI, &MBB); + if (Joined) { + MadeChange = true; continue; + } if (SinkInstruction(MI, SawStore)) ++NumSunk, MadeChange = true; @@ -281,7 +302,7 @@ bool MachineSinking::isWorthBreakingCriticalEdge(MachineInstr *MI, if (!CEBCandidates.insert(std::make_pair(From, To))) return true; - if (!MI->isCopy() && !MI->getDesc().isAsCheapAsAMove()) + if (!MI->isCopy() && !MI->isAsCheapAsAMove()) return true; // MI is cheap, we probably don't want to break the critical edge for it. @@ -372,35 +393,95 @@ static bool AvoidsSinking(MachineInstr *MI, MachineRegisterInfo *MRI) { return MI->isInsertSubreg() || MI->isSubregToReg() || MI->isRegSequence(); } -/// SinkInstruction - Determine whether it is safe to sink the specified machine -/// instruction out of its current block into a successor. -bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) { - // Don't sink insert_subreg, subreg_to_reg, reg_sequence. These are meant to - // be close to the source to make it easier to coalesce. - if (AvoidsSinking(MI, MRI)) +/// collectDebgValues - Scan instructions following MI and collect any +/// matching DBG_VALUEs. +static void collectDebugValues(MachineInstr *MI, + SmallVector & DbgValues) { + DbgValues.clear(); + if (!MI->getOperand(0).isReg()) + return; + + MachineBasicBlock::iterator DI = MI; ++DI; + for (MachineBasicBlock::iterator DE = MI->getParent()->end(); + DI != DE; ++DI) { + if (!DI->isDebugValue()) + return; + if (DI->getOperand(0).isReg() && + DI->getOperand(0).getReg() == MI->getOperand(0).getReg()) + DbgValues.push_back(DI); + } +} + +/// isPostDominatedBy - Return true if A is post dominated by B. +static bool isPostDominatedBy(MachineBasicBlock *A, MachineBasicBlock *B) { + + // FIXME - Use real post dominator. + if (A->succ_size() != 2) + return false; + MachineBasicBlock::succ_iterator I = A->succ_begin(); + if (B == *I) + ++I; + MachineBasicBlock *OtherSuccBlock = *I; + if (OtherSuccBlock->succ_size() != 1 || + *(OtherSuccBlock->succ_begin()) != B) return false; - // Check if it's safe to move the instruction. - if (!MI->isSafeToMove(TII, AA, SawStore)) + return true; +} + +/// isProfitableToSinkTo - Return true if it is profitable to sink MI. +bool MachineSinking::isProfitableToSinkTo(unsigned Reg, MachineInstr *MI, + MachineBasicBlock *MBB, + MachineBasicBlock *SuccToSinkTo) { + assert (MI && "Invalid MachineInstr!"); + assert (SuccToSinkTo && "Invalid SinkTo Candidate BB"); + + if (MBB == SuccToSinkTo) return false; - // FIXME: This should include support for sinking instructions within the - // block they are currently in to shorten the live ranges. We often get - // instructions sunk into the top of a large block, but it would be better to - // also sink them down before their first use in the block. This xform has to - // be careful not to *increase* register pressure though, e.g. sinking - // "x = y + z" down if it kills y and z would increase the live ranges of y - // and z and only shrink the live range of x. + // It is profitable if SuccToSinkTo does not post dominate current block. + if (!isPostDominatedBy(MBB, SuccToSinkTo)) + return true; + + // Check if only use in post dominated block is PHI instruction. + bool NonPHIUse = false; + for (MachineRegisterInfo::use_nodbg_iterator + I = MRI->use_nodbg_begin(Reg), E = MRI->use_nodbg_end(); + I != E; ++I) { + MachineInstr *UseInst = &*I; + MachineBasicBlock *UseBlock = UseInst->getParent(); + if (UseBlock == SuccToSinkTo && !UseInst->isPHI()) + NonPHIUse = true; + } + if (!NonPHIUse) + return true; + + // If SuccToSinkTo post dominates then also it may be profitable if MI + // can further profitably sinked into another block in next round. + bool BreakPHIEdge = false; + // FIXME - If finding successor is compile time expensive then catch results. + if (MachineBasicBlock *MBB2 = FindSuccToSinkTo(MI, SuccToSinkTo, BreakPHIEdge)) + return isProfitableToSinkTo(Reg, MI, SuccToSinkTo, MBB2); + + // If SuccToSinkTo is final destination and it is a post dominator of current + // block then it is not profitable to sink MI into SuccToSinkTo block. + return false; +} + +/// FindSuccToSinkTo - Find a successor to sink this instruction to. +MachineBasicBlock *MachineSinking::FindSuccToSinkTo(MachineInstr *MI, + MachineBasicBlock *MBB, + bool &BreakPHIEdge) { + + assert (MI && "Invalid MachineInstr!"); + assert (MBB && "Invalid MachineBasicBlock!"); // Loop over all the operands of the specified instruction. If there is // anything we can't handle, bail out. - MachineBasicBlock *ParentBlock = MI->getParent(); // SuccToSinkTo - This is the successor to sink this instruction to, once we // decide. MachineBasicBlock *SuccToSinkTo = 0; - - bool BreakPHIEdge = false; for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { const MachineOperand &MO = MI->getOperand(i); if (!MO.isReg()) continue; // Ignore non-register operands. @@ -413,24 +494,11 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) { // If the physreg has no defs anywhere, it's just an ambient register // and we can freely move its uses. Alternatively, if it's allocatable, // it could get allocated to something with a def during allocation. - if (!MRI->def_empty(Reg)) - return false; - - if (AllocatableSet.test(Reg)) - return false; - - // Check for a def among the register's aliases too. - for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) { - unsigned AliasReg = *Alias; - if (!MRI->def_empty(AliasReg)) - return false; - - if (AllocatableSet.test(AliasReg)) - return false; - } + if (!MRI->isConstantPhysReg(Reg, *MBB->getParent())) + return NULL; } else if (!MO.isDead()) { // A def that isn't dead. We can't move it. - return false; + return NULL; } } else { // Virtual register uses are always safe to sink. @@ -438,7 +506,7 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) { // If it's not safe to move defs of the register class, then abort. if (!TII->isSafeToMoveRegClassDefs(MRI->getRegClass(Reg))) - return false; + return NULL; // FIXME: This picks a successor to sink into based on having one // successor that dominates all the uses. However, there are cases where @@ -459,48 +527,82 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) { // If a previous operand picked a block to sink to, then this operand // must be sinkable to the same block. bool LocalUse = false; - if (!AllUsesDominatedByBlock(Reg, SuccToSinkTo, ParentBlock, + if (!AllUsesDominatedByBlock(Reg, SuccToSinkTo, MBB, BreakPHIEdge, LocalUse)) - return false; + return NULL; continue; } // Otherwise, we should look at all the successors and decide which one // we should sink to. - for (MachineBasicBlock::succ_iterator SI = ParentBlock->succ_begin(), - E = ParentBlock->succ_end(); SI != E; ++SI) { + // We give successors with smaller loop depth higher priority. + SmallVector Succs(MBB->succ_begin(), MBB->succ_end()); + std::stable_sort(Succs.begin(), Succs.end(), SuccessorSorter(LI)); + for (SmallVector::iterator SI = Succs.begin(), + E = Succs.end(); SI != E; ++SI) { + MachineBasicBlock *SuccBlock = *SI; bool LocalUse = false; - if (AllUsesDominatedByBlock(Reg, *SI, ParentBlock, + if (AllUsesDominatedByBlock(Reg, SuccBlock, MBB, BreakPHIEdge, LocalUse)) { - SuccToSinkTo = *SI; + SuccToSinkTo = SuccBlock; break; } if (LocalUse) // Def is used locally, it's never safe to move this def. - return false; + return NULL; } // If we couldn't find a block to sink to, ignore this instruction. if (SuccToSinkTo == 0) - return false; + return NULL; + else if (!isProfitableToSinkTo(Reg, MI, MBB, SuccToSinkTo)) + return NULL; } } - // If there are no outputs, it must have side-effects. - if (SuccToSinkTo == 0) - return false; + // It is not possible to sink an instruction into its own block. This can + // happen with loops. + if (MBB == SuccToSinkTo) + return NULL; // It's not safe to sink instructions to EH landing pad. Control flow into // landing pad is implicitly defined. - if (SuccToSinkTo->isLandingPad()) + if (SuccToSinkTo && SuccToSinkTo->isLandingPad()) + return NULL; + + return SuccToSinkTo; +} + +/// SinkInstruction - Determine whether it is safe to sink the specified machine +/// instruction out of its current block into a successor. +bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) { + // Don't sink insert_subreg, subreg_to_reg, reg_sequence. These are meant to + // be close to the source to make it easier to coalesce. + if (AvoidsSinking(MI, MRI)) return false; - // It is not possible to sink an instruction into its own block. This can - // happen with loops. - if (MI->getParent() == SuccToSinkTo) + // Check if it's safe to move the instruction. + if (!MI->isSafeToMove(TII, AA, SawStore)) + return false; + + // FIXME: This should include support for sinking instructions within the + // block they are currently in to shorten the live ranges. We often get + // instructions sunk into the top of a large block, but it would be better to + // also sink them down before their first use in the block. This xform has to + // be careful not to *increase* register pressure though, e.g. sinking + // "x = y + z" down if it kills y and z would increase the live ranges of y + // and z and only shrink the live range of x. + + bool BreakPHIEdge = false; + MachineBasicBlock *ParentBlock = MI->getParent(); + MachineBasicBlock *SuccToSinkTo = FindSuccToSinkTo(MI, ParentBlock, BreakPHIEdge); + + // If there are no outputs, it must have side-effects. + if (SuccToSinkTo == 0) return false; + // If the instruction to move defines a dead physical register which is live // when leaving the basic block, don't move it because it could turn into a // "zombie" define of that preg. E.g., EFLAGS. () @@ -588,10 +690,22 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) { while (InsertPos != SuccToSinkTo->end() && InsertPos->isPHI()) ++InsertPos; + // collect matching debug values. + SmallVector DbgValuesToSink; + collectDebugValues(MI, DbgValuesToSink); + // Move the instruction. SuccToSinkTo->splice(InsertPos, ParentBlock, MI, ++MachineBasicBlock::iterator(MI)); + // Move debug values. + for (SmallVector::iterator DBI = DbgValuesToSink.begin(), + DBE = DbgValuesToSink.end(); DBI != DBE; ++DBI) { + MachineInstr *DbgMI = *DBI; + SuccToSinkTo->splice(InsertPos, ParentBlock, DbgMI, + ++MachineBasicBlock::iterator(DbgMI)); + } + // Conservatively, clear any kill flags, since it's possible that they are no // longer correct. MI->clearKillInfo();