[llvm-commits] [llvm] r85127 - in /llvm/trunk: include/llvm/CodeGen/AntiDepBreaker.h lib/CodeGen/CMakeLists.txt lib/CodeGen/CriticalAntiDepBreaker.cpp lib/CodeGen/CriticalAntiDepBreaker.h lib/CodeGen/PostRASchedulerList.cpp lib/Target/ARM/ARMSubtarget.h test/CodeGen/X86/break-anti-dependencies.ll
David Goodwin
david_goodwin at apple.com
Mon Oct 26 09:59:04 PDT 2009
Author: david_goodwin
Date: Mon Oct 26 11:59:04 2009
New Revision: 85127
URL: http://llvm.org/viewvc/llvm-project?rev=85127&view=rev
Log:
Break anti-dependence breaking out into its own class.
Added:
llvm/trunk/include/llvm/CodeGen/AntiDepBreaker.h
llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.cpp
llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.h
Modified:
llvm/trunk/lib/CodeGen/CMakeLists.txt
llvm/trunk/lib/CodeGen/PostRASchedulerList.cpp
llvm/trunk/lib/Target/ARM/ARMSubtarget.h
llvm/trunk/test/CodeGen/X86/break-anti-dependencies.ll
Added: llvm/trunk/include/llvm/CodeGen/AntiDepBreaker.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/AntiDepBreaker.h?rev=85127&view=auto
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/AntiDepBreaker.h (added)
+++ llvm/trunk/include/llvm/CodeGen/AntiDepBreaker.h Mon Oct 26 11:59:04 2009
@@ -0,0 +1,56 @@
+//=- llvm/CodeGen/AntiDepBreaker.h - Anti-Dependence Breaking -*- C++ -*-=//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the AntiDepBreaker class, which implements
+// anti-dependence breaking heuristics for post-register-allocation scheduling.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_ANTIDEPBREAKER_H
+#define LLVM_CODEGEN_ANTIDEPBREAKER_H
+
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/ScheduleDAG.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+
+namespace llvm {
+
+/// AntiDepBreaker - This class works into conjunction with the
+/// post-RA scheduler to rename registers to break register
+/// anti-dependencies.
+class AntiDepBreaker {
+public:
+ /// Start - Initialize anti-dep breaking for a new basic block.
+ virtual void StartBlock(MachineBasicBlock *BB) =0;
+
+ /// BreakAntiDependencies - Identifiy anti-dependencies within a
+ /// basic-block region and break them by renaming registers. Return
+ /// the number of anti-dependencies broken.
+ ///
+ virtual unsigned BreakAntiDependencies(std::vector<SUnit>& SUnits,
+ MachineBasicBlock::iterator& Begin,
+ MachineBasicBlock::iterator& End,
+ unsigned InsertPosIndex) =0;
+
+ /// Observe - Update liveness information to account for the current
+ /// instruction, which will not be scheduled.
+ ///
+ virtual void Observe(MachineInstr *MI, unsigned Count,
+ unsigned InsertPosIndex) =0;
+
+ /// Finish - Finish anti-dep breaking for a basic block.
+ virtual void FinishBlock() =0;
+};
+
+}
+
+#endif
Modified: llvm/trunk/lib/CodeGen/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CMakeLists.txt?rev=85127&r1=85126&r2=85127&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/CMakeLists.txt (original)
+++ llvm/trunk/lib/CodeGen/CMakeLists.txt Mon Oct 26 11:59:04 2009
@@ -1,6 +1,7 @@
add_llvm_library(LLVMCodeGen
BranchFolding.cpp
CodePlacementOpt.cpp
+ CriticalAntiDepBreaker.cpp
DeadMachineInstructionElim.cpp
DwarfEHPrepare.cpp
ELFCodeEmitter.cpp
Added: llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.cpp?rev=85127&view=auto
==============================================================================
--- llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.cpp (added)
+++ llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.cpp Mon Oct 26 11:59:04 2009
@@ -0,0 +1,539 @@
+//===----- CriticalAntiDepBreaker.cpp - Anti-dep breaker -------- ---------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the CriticalAntiDepBreaker class, which
+// implements register anti-dependence breaking along a blocks
+// critical path during post-RA scheduler.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "critical-antidep"
+#include "CriticalAntiDepBreaker.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+CriticalAntiDepBreaker::
+CriticalAntiDepBreaker(MachineFunction& MFi) :
+ AntiDepBreaker(), MF(MFi),
+ MRI(MF.getRegInfo()),
+ TRI(MF.getTarget().getRegisterInfo()),
+ AllocatableSet(TRI->getAllocatableSet(MF))
+{
+}
+
+CriticalAntiDepBreaker::~CriticalAntiDepBreaker() {
+}
+
+void CriticalAntiDepBreaker::StartBlock(MachineBasicBlock *BB) {
+ // Clear out the register class data.
+ std::fill(Classes, array_endof(Classes),
+ static_cast<const TargetRegisterClass *>(0));
+
+ // Initialize the indices to indicate that no registers are live.
+ std::fill(KillIndices, array_endof(KillIndices), ~0u);
+ std::fill(DefIndices, array_endof(DefIndices), BB->size());
+
+ // Clear "do not change" set.
+ KeepRegs.clear();
+
+ bool IsReturnBlock = (!BB->empty() && BB->back().getDesc().isReturn());
+
+ // Determine the live-out physregs for this block.
+ if (IsReturnBlock) {
+ // In a return block, examine the function live-out regs.
+ for (MachineRegisterInfo::liveout_iterator I = MRI.liveout_begin(),
+ E = MRI.liveout_end(); I != E; ++I) {
+ unsigned Reg = *I;
+ Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ KillIndices[Reg] = BB->size();
+ DefIndices[Reg] = ~0u;
+ // Repeat, for all aliases.
+ for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
+ unsigned AliasReg = *Alias;
+ Classes[AliasReg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ KillIndices[AliasReg] = BB->size();
+ DefIndices[AliasReg] = ~0u;
+ }
+ }
+ } else {
+ // In a non-return block, examine the live-in regs of all successors.
+ for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
+ SE = BB->succ_end(); SI != SE; ++SI)
+ for (MachineBasicBlock::livein_iterator I = (*SI)->livein_begin(),
+ E = (*SI)->livein_end(); I != E; ++I) {
+ unsigned Reg = *I;
+ Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ KillIndices[Reg] = BB->size();
+ DefIndices[Reg] = ~0u;
+ // Repeat, for all aliases.
+ for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
+ unsigned AliasReg = *Alias;
+ Classes[AliasReg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ KillIndices[AliasReg] = BB->size();
+ DefIndices[AliasReg] = ~0u;
+ }
+ }
+ }
+
+ // Mark live-out callee-saved registers. In a return block this is
+ // all callee-saved registers. In non-return this is any
+ // callee-saved register that is not saved in the prolog.
+ const MachineFrameInfo *MFI = MF.getFrameInfo();
+ BitVector Pristine = MFI->getPristineRegs(BB);
+ for (const unsigned *I = TRI->getCalleeSavedRegs(); *I; ++I) {
+ unsigned Reg = *I;
+ if (!IsReturnBlock && !Pristine.test(Reg)) continue;
+ Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ KillIndices[Reg] = BB->size();
+ DefIndices[Reg] = ~0u;
+ // Repeat, for all aliases.
+ for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
+ unsigned AliasReg = *Alias;
+ Classes[AliasReg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ KillIndices[AliasReg] = BB->size();
+ DefIndices[AliasReg] = ~0u;
+ }
+ }
+}
+
+void CriticalAntiDepBreaker::FinishBlock() {
+ RegRefs.clear();
+ KeepRegs.clear();
+}
+
+void CriticalAntiDepBreaker::Observe(MachineInstr *MI, unsigned Count,
+ unsigned InsertPosIndex) {
+ assert(Count < InsertPosIndex && "Instruction index out of expected range!");
+
+ // Any register which was defined within the previous scheduling region
+ // may have been rescheduled and its lifetime may overlap with registers
+ // in ways not reflected in our current liveness state. For each such
+ // register, adjust the liveness state to be conservatively correct.
+ for (unsigned Reg = 0; Reg != TargetRegisterInfo::FirstVirtualRegister; ++Reg)
+ if (DefIndices[Reg] < InsertPosIndex && DefIndices[Reg] >= Count) {
+ assert(KillIndices[Reg] == ~0u && "Clobbered register is live!");
+ // Mark this register to be non-renamable.
+ Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ // Move the def index to the end of the previous region, to reflect
+ // that the def could theoretically have been scheduled at the end.
+ DefIndices[Reg] = InsertPosIndex;
+ }
+
+ PrescanInstruction(MI);
+ ScanInstruction(MI, Count);
+}
+
+/// CriticalPathStep - Return the next SUnit after SU on the bottom-up
+/// critical path.
+static SDep *CriticalPathStep(SUnit *SU) {
+ SDep *Next = 0;
+ unsigned NextDepth = 0;
+ // Find the predecessor edge with the greatest depth.
+ for (SUnit::pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
+ P != PE; ++P) {
+ SUnit *PredSU = P->getSUnit();
+ unsigned PredLatency = P->getLatency();
+ unsigned PredTotalLatency = PredSU->getDepth() + PredLatency;
+ // In the case of a latency tie, prefer an anti-dependency edge over
+ // other types of edges.
+ if (NextDepth < PredTotalLatency ||
+ (NextDepth == PredTotalLatency && P->getKind() == SDep::Anti)) {
+ NextDepth = PredTotalLatency;
+ Next = &*P;
+ }
+ }
+ return Next;
+}
+
+void CriticalAntiDepBreaker::PrescanInstruction(MachineInstr *MI) {
+ // Scan the register operands for this instruction and update
+ // Classes and RegRefs.
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isReg()) continue;
+ unsigned Reg = MO.getReg();
+ if (Reg == 0) continue;
+ const TargetRegisterClass *NewRC = 0;
+
+ if (i < MI->getDesc().getNumOperands())
+ NewRC = MI->getDesc().OpInfo[i].getRegClass(TRI);
+
+ // For now, only allow the register to be changed if its register
+ // class is consistent across all uses.
+ if (!Classes[Reg] && NewRC)
+ Classes[Reg] = NewRC;
+ else if (!NewRC || Classes[Reg] != NewRC)
+ Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
+
+ // Now check for aliases.
+ for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
+ // If an alias of the reg is used during the live range, give up.
+ // Note that this allows us to skip checking if AntiDepReg
+ // overlaps with any of the aliases, among other things.
+ unsigned AliasReg = *Alias;
+ if (Classes[AliasReg]) {
+ Classes[AliasReg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ }
+ }
+
+ // If we're still willing to consider this register, note the reference.
+ if (Classes[Reg] != reinterpret_cast<TargetRegisterClass *>(-1))
+ RegRefs.insert(std::make_pair(Reg, &MO));
+
+ // It's not safe to change register allocation for source operands of
+ // that have special allocation requirements.
+ if (MO.isUse() && MI->getDesc().hasExtraSrcRegAllocReq()) {
+ if (KeepRegs.insert(Reg)) {
+ for (const unsigned *Subreg = TRI->getSubRegisters(Reg);
+ *Subreg; ++Subreg)
+ KeepRegs.insert(*Subreg);
+ }
+ }
+ }
+}
+
+void CriticalAntiDepBreaker::ScanInstruction(MachineInstr *MI,
+ unsigned Count) {
+ // Update liveness.
+ // Proceding upwards, registers that are defed but not used in this
+ // instruction are now dead.
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isReg()) continue;
+ unsigned Reg = MO.getReg();
+ if (Reg == 0) continue;
+ if (!MO.isDef()) continue;
+ // Ignore two-addr defs.
+ if (MI->isRegTiedToUseOperand(i)) continue;
+
+ DefIndices[Reg] = Count;
+ KillIndices[Reg] = ~0u;
+ assert(((KillIndices[Reg] == ~0u) !=
+ (DefIndices[Reg] == ~0u)) &&
+ "Kill and Def maps aren't consistent for Reg!");
+ KeepRegs.erase(Reg);
+ Classes[Reg] = 0;
+ RegRefs.erase(Reg);
+ // Repeat, for all subregs.
+ for (const unsigned *Subreg = TRI->getSubRegisters(Reg);
+ *Subreg; ++Subreg) {
+ unsigned SubregReg = *Subreg;
+ DefIndices[SubregReg] = Count;
+ KillIndices[SubregReg] = ~0u;
+ KeepRegs.erase(SubregReg);
+ Classes[SubregReg] = 0;
+ RegRefs.erase(SubregReg);
+ }
+ // Conservatively mark super-registers as unusable.
+ for (const unsigned *Super = TRI->getSuperRegisters(Reg);
+ *Super; ++Super) {
+ unsigned SuperReg = *Super;
+ Classes[SuperReg] = reinterpret_cast<TargetRegisterClass *>(-1);
+ }
+ }
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isReg()) continue;
+ unsigned Reg = MO.getReg();
+ if (Reg == 0) continue;
+ if (!MO.isUse()) continue;
+
+ const TargetRegisterClass *NewRC = 0;
+ if (i < MI->getDesc().getNumOperands())
+ NewRC = MI->getDesc().OpInfo[i].getRegClass(TRI);
+
+ // For now, only allow the register to be changed if its register
+ // class is consistent across all uses.
+ if (!Classes[Reg] && NewRC)
+ Classes[Reg] = NewRC;
+ else if (!NewRC || Classes[Reg] != NewRC)
+ Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
+
+ RegRefs.insert(std::make_pair(Reg, &MO));
+
+ // It wasn't previously live but now it is, this is a kill.
+ if (KillIndices[Reg] == ~0u) {
+ KillIndices[Reg] = Count;
+ DefIndices[Reg] = ~0u;
+ assert(((KillIndices[Reg] == ~0u) !=
+ (DefIndices[Reg] == ~0u)) &&
+ "Kill and Def maps aren't consistent for Reg!");
+ }
+ // Repeat, for all aliases.
+ for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
+ unsigned AliasReg = *Alias;
+ if (KillIndices[AliasReg] == ~0u) {
+ KillIndices[AliasReg] = Count;
+ DefIndices[AliasReg] = ~0u;
+ }
+ }
+ }
+}
+
+unsigned
+CriticalAntiDepBreaker::findSuitableFreeRegister(unsigned AntiDepReg,
+ unsigned LastNewReg,
+ const TargetRegisterClass *RC) {
+ for (TargetRegisterClass::iterator R = RC->allocation_order_begin(MF),
+ RE = RC->allocation_order_end(MF); R != RE; ++R) {
+ unsigned NewReg = *R;
+ // Don't replace a register with itself.
+ if (NewReg == AntiDepReg) continue;
+ // Don't replace a register with one that was recently used to repair
+ // an anti-dependence with this AntiDepReg, because that would
+ // re-introduce that anti-dependence.
+ if (NewReg == LastNewReg) continue;
+ // If NewReg is dead and NewReg's most recent def is not before
+ // AntiDepReg's kill, it's safe to replace AntiDepReg with NewReg.
+ assert(((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u)) &&
+ "Kill and Def maps aren't consistent for AntiDepReg!");
+ assert(((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u)) &&
+ "Kill and Def maps aren't consistent for NewReg!");
+ if (KillIndices[NewReg] != ~0u ||
+ Classes[NewReg] == reinterpret_cast<TargetRegisterClass *>(-1) ||
+ KillIndices[AntiDepReg] > DefIndices[NewReg])
+ continue;
+ return NewReg;
+ }
+
+ // No registers are free and available!
+ return 0;
+}
+
+unsigned CriticalAntiDepBreaker::
+BreakAntiDependencies(std::vector<SUnit>& SUnits,
+ MachineBasicBlock::iterator& Begin,
+ MachineBasicBlock::iterator& End,
+ unsigned InsertPosIndex) {
+ // The code below assumes that there is at least one instruction,
+ // so just duck out immediately if the block is empty.
+ if (SUnits.empty()) return 0;
+
+ // Find the node at the bottom of the critical path.
+ SUnit *Max = 0;
+ for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
+ SUnit *SU = &SUnits[i];
+ if (!Max || SU->getDepth() + SU->Latency > Max->getDepth() + Max->Latency)
+ Max = SU;
+ }
+
+#ifndef NDEBUG
+ {
+ DEBUG(errs() << "Critical path has total latency "
+ << (Max->getDepth() + Max->Latency) << "\n");
+ DEBUG(errs() << "Available regs:");
+ for (unsigned Reg = 0; Reg < TRI->getNumRegs(); ++Reg) {
+ if (KillIndices[Reg] == ~0u)
+ DEBUG(errs() << " " << TRI->getName(Reg));
+ }
+ DEBUG(errs() << '\n');
+ }
+#endif
+
+ // Track progress along the critical path through the SUnit graph as we walk
+ // the instructions.
+ SUnit *CriticalPathSU = Max;
+ MachineInstr *CriticalPathMI = CriticalPathSU->getInstr();
+
+ // Consider this pattern:
+ // A = ...
+ // ... = A
+ // A = ...
+ // ... = A
+ // A = ...
+ // ... = A
+ // A = ...
+ // ... = A
+ // There are three anti-dependencies here, and without special care,
+ // we'd break all of them using the same register:
+ // A = ...
+ // ... = A
+ // B = ...
+ // ... = B
+ // B = ...
+ // ... = B
+ // B = ...
+ // ... = B
+ // because at each anti-dependence, B is the first register that
+ // isn't A which is free. This re-introduces anti-dependencies
+ // at all but one of the original anti-dependencies that we were
+ // trying to break. To avoid this, keep track of the most recent
+ // register that each register was replaced with, avoid
+ // using it to repair an anti-dependence on the same register.
+ // This lets us produce this:
+ // A = ...
+ // ... = A
+ // B = ...
+ // ... = B
+ // C = ...
+ // ... = C
+ // B = ...
+ // ... = B
+ // This still has an anti-dependence on B, but at least it isn't on the
+ // original critical path.
+ //
+ // TODO: If we tracked more than one register here, we could potentially
+ // fix that remaining critical edge too. This is a little more involved,
+ // because unlike the most recent register, less recent registers should
+ // still be considered, though only if no other registers are available.
+ unsigned LastNewReg[TargetRegisterInfo::FirstVirtualRegister] = {};
+
+ // Attempt to break anti-dependence edges on the critical path. Walk the
+ // instructions from the bottom up, tracking information about liveness
+ // as we go to help determine which registers are available.
+ unsigned Broken = 0;
+ unsigned Count = InsertPosIndex - 1;
+ for (MachineBasicBlock::iterator I = End, E = Begin;
+ I != E; --Count) {
+ MachineInstr *MI = --I;
+
+ // Check if this instruction has a dependence on the critical path that
+ // is an anti-dependence that we may be able to break. If it is, set
+ // AntiDepReg to the non-zero register associated with the anti-dependence.
+ //
+ // We limit our attention to the critical path as a heuristic to avoid
+ // breaking anti-dependence edges that aren't going to significantly
+ // impact the overall schedule. There are a limited number of registers
+ // and we want to save them for the important edges.
+ //
+ // TODO: Instructions with multiple defs could have multiple
+ // anti-dependencies. The current code here only knows how to break one
+ // edge per instruction. Note that we'd have to be able to break all of
+ // the anti-dependencies in an instruction in order to be effective.
+ unsigned AntiDepReg = 0;
+ if (MI == CriticalPathMI) {
+ if (SDep *Edge = CriticalPathStep(CriticalPathSU)) {
+ SUnit *NextSU = Edge->getSUnit();
+
+ // Only consider anti-dependence edges.
+ if (Edge->getKind() == SDep::Anti) {
+ AntiDepReg = Edge->getReg();
+ assert(AntiDepReg != 0 && "Anti-dependence on reg0?");
+ if (!AllocatableSet.test(AntiDepReg))
+ // Don't break anti-dependencies on non-allocatable registers.
+ AntiDepReg = 0;
+ else if (KeepRegs.count(AntiDepReg))
+ // Don't break anti-dependencies if an use down below requires
+ // this exact register.
+ AntiDepReg = 0;
+ else {
+ // If the SUnit has other dependencies on the SUnit that it
+ // anti-depends on, don't bother breaking the anti-dependency
+ // since those edges would prevent such units from being
+ // scheduled past each other regardless.
+ //
+ // Also, if there are dependencies on other SUnits with the
+ // same register as the anti-dependency, don't attempt to
+ // break it.
+ for (SUnit::pred_iterator P = CriticalPathSU->Preds.begin(),
+ PE = CriticalPathSU->Preds.end(); P != PE; ++P)
+ if (P->getSUnit() == NextSU ?
+ (P->getKind() != SDep::Anti || P->getReg() != AntiDepReg) :
+ (P->getKind() == SDep::Data && P->getReg() == AntiDepReg)) {
+ AntiDepReg = 0;
+ break;
+ }
+ }
+ }
+ CriticalPathSU = NextSU;
+ CriticalPathMI = CriticalPathSU->getInstr();
+ } else {
+ // We've reached the end of the critical path.
+ CriticalPathSU = 0;
+ CriticalPathMI = 0;
+ }
+ }
+
+ PrescanInstruction(MI);
+
+ if (MI->getDesc().hasExtraDefRegAllocReq())
+ // If this instruction's defs have special allocation requirement, don't
+ // break this anti-dependency.
+ AntiDepReg = 0;
+ else if (AntiDepReg) {
+ // If this instruction has a use of AntiDepReg, breaking it
+ // is invalid.
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isReg()) continue;
+ unsigned Reg = MO.getReg();
+ if (Reg == 0) continue;
+ if (MO.isUse() && AntiDepReg == Reg) {
+ AntiDepReg = 0;
+ break;
+ }
+ }
+ }
+
+ // Determine AntiDepReg's register class, if it is live and is
+ // consistently used within a single class.
+ const TargetRegisterClass *RC = AntiDepReg != 0 ? Classes[AntiDepReg] : 0;
+ assert((AntiDepReg == 0 || RC != NULL) &&
+ "Register should be live if it's causing an anti-dependence!");
+ if (RC == reinterpret_cast<TargetRegisterClass *>(-1))
+ AntiDepReg = 0;
+
+ // Look for a suitable register to use to break the anti-depenence.
+ //
+ // TODO: Instead of picking the first free register, consider which might
+ // be the best.
+ if (AntiDepReg != 0) {
+ if (unsigned NewReg = findSuitableFreeRegister(AntiDepReg,
+ LastNewReg[AntiDepReg],
+ RC)) {
+ DEBUG(errs() << "Breaking anti-dependence edge on "
+ << TRI->getName(AntiDepReg)
+ << " with " << RegRefs.count(AntiDepReg) << " references"
+ << " using " << TRI->getName(NewReg) << "!\n");
+
+ // Update the references to the old register to refer to the new
+ // register.
+ std::pair<std::multimap<unsigned, MachineOperand *>::iterator,
+ std::multimap<unsigned, MachineOperand *>::iterator>
+ Range = RegRefs.equal_range(AntiDepReg);
+ for (std::multimap<unsigned, MachineOperand *>::iterator
+ Q = Range.first, QE = Range.second; Q != QE; ++Q)
+ Q->second->setReg(NewReg);
+
+ // We just went back in time and modified history; the
+ // liveness information for the anti-depenence reg is now
+ // inconsistent. Set the state as if it were dead.
+ Classes[NewReg] = Classes[AntiDepReg];
+ DefIndices[NewReg] = DefIndices[AntiDepReg];
+ KillIndices[NewReg] = KillIndices[AntiDepReg];
+ assert(((KillIndices[NewReg] == ~0u) !=
+ (DefIndices[NewReg] == ~0u)) &&
+ "Kill and Def maps aren't consistent for NewReg!");
+
+ Classes[AntiDepReg] = 0;
+ DefIndices[AntiDepReg] = KillIndices[AntiDepReg];
+ KillIndices[AntiDepReg] = ~0u;
+ assert(((KillIndices[AntiDepReg] == ~0u) !=
+ (DefIndices[AntiDepReg] == ~0u)) &&
+ "Kill and Def maps aren't consistent for AntiDepReg!");
+
+ RegRefs.erase(AntiDepReg);
+ LastNewReg[AntiDepReg] = NewReg;
+ ++Broken;
+ }
+ }
+
+ ScanInstruction(MI, Count);
+ }
+
+ return Broken;
+}
Added: llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.h?rev=85127&view=auto
==============================================================================
--- llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.h (added)
+++ llvm/trunk/lib/CodeGen/CriticalAntiDepBreaker.h Mon Oct 26 11:59:04 2009
@@ -0,0 +1,95 @@
+//=- llvm/CodeGen/CriticalAntiDepBreaker.h - Anti-Dep Support -*- C++ -*-=//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the CriticalAntiDepBreaker class, which
+// implements register anti-dependence breaking along a blocks
+// critical path during post-RA scheduler.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_CRITICALANTIDEPBREAKER_H
+#define LLVM_CODEGEN_CRITICALANTIDEPBREAKER_H
+
+#include "llvm/CodeGen/AntiDepBreaker.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/ScheduleDAG.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/SmallSet.h"
+
+namespace llvm {
+ class CriticalAntiDepBreaker : public AntiDepBreaker {
+ MachineFunction& MF;
+ MachineRegisterInfo &MRI;
+ const TargetRegisterInfo *TRI;
+
+ /// AllocatableSet - The set of allocatable registers.
+ /// We'll be ignoring anti-dependencies on non-allocatable registers,
+ /// because they may not be safe to break.
+ const BitVector AllocatableSet;
+
+ /// Classes - For live regs that are only used in one register class in a
+ /// live range, the register class. If the register is not live, the
+ /// corresponding value is null. If the register is live but used in
+ /// multiple register classes, the corresponding value is -1 casted to a
+ /// pointer.
+ const TargetRegisterClass *
+ Classes[TargetRegisterInfo::FirstVirtualRegister];
+
+ /// RegRegs - Map registers to all their references within a live range.
+ std::multimap<unsigned, MachineOperand *> RegRefs;
+
+ /// KillIndices - The index of the most recent kill (proceding bottom-up),
+ /// or ~0u if the register is not live.
+ unsigned KillIndices[TargetRegisterInfo::FirstVirtualRegister];
+
+ /// DefIndices - The index of the most recent complete def (proceding bottom
+ /// up), or ~0u if the register is live.
+ unsigned DefIndices[TargetRegisterInfo::FirstVirtualRegister];
+
+ /// KeepRegs - A set of registers which are live and cannot be changed to
+ /// break anti-dependencies.
+ SmallSet<unsigned, 4> KeepRegs;
+
+ public:
+ CriticalAntiDepBreaker(MachineFunction& MFi);
+ ~CriticalAntiDepBreaker();
+
+ /// Start - Initialize anti-dep breaking for a new basic block.
+ void StartBlock(MachineBasicBlock *BB);
+
+ /// BreakAntiDependencies - Identifiy anti-dependencies along the critical path
+ /// of the ScheduleDAG and break them by renaming registers.
+ ///
+ unsigned BreakAntiDependencies(std::vector<SUnit>& SUnits,
+ MachineBasicBlock::iterator& Begin,
+ MachineBasicBlock::iterator& End,
+ unsigned InsertPosIndex);
+
+ /// Observe - Update liveness information to account for the current
+ /// instruction, which will not be scheduled.
+ ///
+ void Observe(MachineInstr *MI, unsigned Count, unsigned InsertPosIndex);
+
+ /// Finish - Finish anti-dep breaking for a basic block.
+ void FinishBlock();
+
+ private:
+ void PrescanInstruction(MachineInstr *MI);
+ void ScanInstruction(MachineInstr *MI, unsigned Count);
+ unsigned findSuitableFreeRegister(unsigned AntiDepReg,
+ unsigned LastNewReg,
+ const TargetRegisterClass *);
+ };
+}
+
+#endif
Modified: llvm/trunk/lib/CodeGen/PostRASchedulerList.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/PostRASchedulerList.cpp?rev=85127&r1=85126&r2=85127&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/PostRASchedulerList.cpp (original)
+++ llvm/trunk/lib/CodeGen/PostRASchedulerList.cpp Mon Oct 26 11:59:04 2009
@@ -19,6 +19,7 @@
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "post-RA-sched"
+#include "CriticalAntiDepBreaker.h"
#include "ExactHazardRecognizer.h"
#include "SimpleHazardRecognizer.h"
#include "ScheduleDAGInstrs.h"
@@ -40,6 +41,7 @@
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
+#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/Statistic.h"
#include <map>
#include <set>
@@ -47,6 +49,7 @@
STATISTIC(NumNoops, "Number of noops inserted");
STATISTIC(NumStalls, "Number of pipeline stalls");
+STATISTIC(NumFixedAnti, "Number of fixed anti-dependencies");
// Post-RA scheduling is enabled with
// TargetSubtarget.enablePostRAScheduler(). This flag can be used to
@@ -55,10 +58,11 @@
EnablePostRAScheduler("post-RA-scheduler",
cl::desc("Enable scheduling after register allocation"),
cl::init(false), cl::Hidden);
-static cl::opt<bool>
+static cl::opt<std::string>
EnableAntiDepBreaking("break-anti-dependencies",
- cl::desc("Break post-RA scheduling anti-dependencies"),
- cl::init(true), cl::Hidden);
+ cl::desc("Break post-RA scheduling anti-dependencies: "
+ "\"critical\", \"all\", or \"none\""),
+ cl::init("none"), cl::Hidden);
static cl::opt<bool>
EnablePostRAHazardAvoidance("avoid-hazards",
cl::desc("Enable exact hazard avoidance"),
@@ -116,56 +120,30 @@
/// Topo - A topological ordering for SUnits.
ScheduleDAGTopologicalSort Topo;
- /// AllocatableSet - The set of allocatable registers.
- /// We'll be ignoring anti-dependencies on non-allocatable registers,
- /// because they may not be safe to break.
- const BitVector AllocatableSet;
-
/// HazardRec - The hazard recognizer to use.
ScheduleHazardRecognizer *HazardRec;
+ /// AntiDepBreak - Anti-dependence breaking object, or NULL if none
+ AntiDepBreaker *AntiDepBreak;
+
/// AA - AliasAnalysis for making memory reference queries.
AliasAnalysis *AA;
- /// AntiDepMode - Anti-dependence breaking mode
- TargetSubtarget::AntiDepBreakMode AntiDepMode;
-
- /// Classes - For live regs that are only used in one register class in a
- /// live range, the register class. If the register is not live, the
- /// corresponding value is null. If the register is live but used in
- /// multiple register classes, the corresponding value is -1 casted to a
- /// pointer.
- const TargetRegisterClass *
- Classes[TargetRegisterInfo::FirstVirtualRegister];
-
- /// RegRegs - Map registers to all their references within a live range.
- std::multimap<unsigned, MachineOperand *> RegRefs;
-
/// KillIndices - The index of the most recent kill (proceding bottom-up),
/// or ~0u if the register is not live.
unsigned KillIndices[TargetRegisterInfo::FirstVirtualRegister];
- /// DefIndices - The index of the most recent complete def (proceding bottom
- /// up), or ~0u if the register is live.
- unsigned DefIndices[TargetRegisterInfo::FirstVirtualRegister];
-
- /// KeepRegs - A set of registers which are live and cannot be changed to
- /// break anti-dependencies.
- SmallSet<unsigned, 4> KeepRegs;
-
public:
SchedulePostRATDList(MachineFunction &MF,
const MachineLoopInfo &MLI,
const MachineDominatorTree &MDT,
ScheduleHazardRecognizer *HR,
- AliasAnalysis *aa,
- TargetSubtarget::AntiDepBreakMode adm)
+ AntiDepBreaker *ADB,
+ AliasAnalysis *aa)
: ScheduleDAGInstrs(MF, MLI, MDT), Topo(SUnits),
- AllocatableSet(TRI->getAllocatableSet(MF)),
- HazardRec(HR), AA(aa), AntiDepMode(adm) {}
+ HazardRec(HR), AntiDepBreak(ADB), AA(aa) {}
~SchedulePostRATDList() {
- delete HazardRec;
}
/// StartBlock - Initialize register live-range state for scheduling in
@@ -177,11 +155,6 @@
///
void Schedule();
- /// FixupKills - Fix register kill flags that have been made
- /// invalid due to scheduling
- ///
- void FixupKills(MachineBasicBlock *MBB);
-
/// Observe - Update liveness information to account for the current
/// instruction, which will not be scheduled.
///
@@ -191,17 +164,16 @@
///
void FinishBlock();
+ /// FixupKills - Fix register kill flags that have been made
+ /// invalid due to scheduling
+ ///
+ void FixupKills(MachineBasicBlock *MBB);
+
private:
- void PrescanInstruction(MachineInstr *MI);
- void ScanInstruction(MachineInstr *MI, unsigned Count);
void ReleaseSucc(SUnit *SU, SDep *SuccEdge);
void ReleaseSuccessors(SUnit *SU);
void ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle);
void ListScheduleTopDown();
- bool BreakAntiDependencies();
- unsigned findSuitableFreeRegister(unsigned AntiDepReg,
- unsigned LastNewReg,
- const TargetRegisterClass *);
void StartBlockForKills(MachineBasicBlock *BB);
// ToggleKillFlag - Toggle a register operand kill flag. Other
@@ -250,8 +222,9 @@
// Check for antidep breaking override...
if (EnableAntiDepBreaking.getPosition() > 0) {
- AntiDepMode = (EnableAntiDepBreaking) ?
- TargetSubtarget::ANTIDEP_CRITICAL : TargetSubtarget::ANTIDEP_NONE;
+ AntiDepMode = (EnableAntiDepBreaking == "all") ? TargetSubtarget::ANTIDEP_ALL :
+ (EnableAntiDepBreaking == "critical") ? TargetSubtarget::ANTIDEP_CRITICAL :
+ TargetSubtarget::ANTIDEP_NONE;
}
DEBUG(errs() << "PostRAScheduler\n");
@@ -262,8 +235,12 @@
ScheduleHazardRecognizer *HR = EnablePostRAHazardAvoidance ?
(ScheduleHazardRecognizer *)new ExactHazardRecognizer(InstrItins) :
(ScheduleHazardRecognizer *)new SimpleHazardRecognizer();
+ AntiDepBreaker *ADB =
+ (AntiDepMode == TargetSubtarget::ANTIDEP_ALL) ? NULL /* FIXME */ :
+ (AntiDepMode == TargetSubtarget::ANTIDEP_CRITICAL) ?
+ new CriticalAntiDepBreaker(Fn) : NULL;
- SchedulePostRATDList Scheduler(Fn, MLI, MDT, HR, AA, AntiDepMode);
+ SchedulePostRATDList Scheduler(Fn, MLI, MDT, HR, ADB, AA);
// Loop over all of the basic blocks
for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
@@ -311,6 +288,9 @@
Scheduler.FixupKills(MBB);
}
+ delete HR;
+ delete ADB;
+
return true;
}
@@ -321,78 +301,10 @@
// Call the superclass.
ScheduleDAGInstrs::StartBlock(BB);
- // Reset the hazard recognizer.
+ // Reset the hazard recognizer and anti-dep breaker.
HazardRec->Reset();
-
- // Clear out the register class data.
- std::fill(Classes, array_endof(Classes),
- static_cast<const TargetRegisterClass *>(0));
-
- // Initialize the indices to indicate that no registers are live.
- std::fill(KillIndices, array_endof(KillIndices), ~0u);
- std::fill(DefIndices, array_endof(DefIndices), BB->size());
-
- // Clear "do not change" set.
- KeepRegs.clear();
-
- bool IsReturnBlock = (!BB->empty() && BB->back().getDesc().isReturn());
-
- // Determine the live-out physregs for this block.
- if (IsReturnBlock) {
- // In a return block, examine the function live-out regs.
- for (MachineRegisterInfo::liveout_iterator I = MRI.liveout_begin(),
- E = MRI.liveout_end(); I != E; ++I) {
- unsigned Reg = *I;
- Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
- KillIndices[Reg] = BB->size();
- DefIndices[Reg] = ~0u;
- // Repeat, for all aliases.
- for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
- unsigned AliasReg = *Alias;
- Classes[AliasReg] = reinterpret_cast<TargetRegisterClass *>(-1);
- KillIndices[AliasReg] = BB->size();
- DefIndices[AliasReg] = ~0u;
- }
- }
- } else {
- // In a non-return block, examine the live-in regs of all successors.
- for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
- SE = BB->succ_end(); SI != SE; ++SI)
- for (MachineBasicBlock::livein_iterator I = (*SI)->livein_begin(),
- E = (*SI)->livein_end(); I != E; ++I) {
- unsigned Reg = *I;
- Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
- KillIndices[Reg] = BB->size();
- DefIndices[Reg] = ~0u;
- // Repeat, for all aliases.
- for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
- unsigned AliasReg = *Alias;
- Classes[AliasReg] = reinterpret_cast<TargetRegisterClass *>(-1);
- KillIndices[AliasReg] = BB->size();
- DefIndices[AliasReg] = ~0u;
- }
- }
- }
-
- // Mark live-out callee-saved registers. In a return block this is
- // all callee-saved registers. In non-return this is any
- // callee-saved register that is not saved in the prolog.
- const MachineFrameInfo *MFI = MF.getFrameInfo();
- BitVector Pristine = MFI->getPristineRegs(BB);
- for (const unsigned *I = TRI->getCalleeSavedRegs(); *I; ++I) {
- unsigned Reg = *I;
- if (!IsReturnBlock && !Pristine.test(Reg)) continue;
- Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
- KillIndices[Reg] = BB->size();
- DefIndices[Reg] = ~0u;
- // Repeat, for all aliases.
- for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
- unsigned AliasReg = *Alias;
- Classes[AliasReg] = reinterpret_cast<TargetRegisterClass *>(-1);
- KillIndices[AliasReg] = BB->size();
- DefIndices[AliasReg] = ~0u;
- }
- }
+ if (AntiDepBreak != NULL)
+ AntiDepBreak->StartBlock(BB);
}
/// Schedule - Schedule the instruction range using list scheduling.
@@ -403,8 +315,11 @@
// Build the scheduling graph.
BuildSchedGraph(AA);
- if (AntiDepMode != TargetSubtarget::ANTIDEP_NONE) {
- if (BreakAntiDependencies()) {
+ if (AntiDepBreak != NULL) {
+ unsigned Broken =
+ AntiDepBreak->BreakAntiDependencies(SUnits, Begin, InsertPos,
+ InsertPosIndex);
+ if (Broken > 0) {
// We made changes. Update the dependency graph.
// Theoretically we could update the graph in place:
// When a live range is changed to use a different register, remove
@@ -415,6 +330,8 @@
EntrySU = SUnit();
ExitSU = SUnit();
BuildSchedGraph(AA);
+
+ NumFixedAnti += Broken;
}
}
@@ -432,436 +349,20 @@
/// instruction, which will not be scheduled.
///
void SchedulePostRATDList::Observe(MachineInstr *MI, unsigned Count) {
- assert(Count < InsertPosIndex && "Instruction index out of expected range!");
-
- // Any register which was defined within the previous scheduling region
- // may have been rescheduled and its lifetime may overlap with registers
- // in ways not reflected in our current liveness state. For each such
- // register, adjust the liveness state to be conservatively correct.
- for (unsigned Reg = 0; Reg != TargetRegisterInfo::FirstVirtualRegister; ++Reg)
- if (DefIndices[Reg] < InsertPosIndex && DefIndices[Reg] >= Count) {
- assert(KillIndices[Reg] == ~0u && "Clobbered register is live!");
- // Mark this register to be non-renamable.
- Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
- // Move the def index to the end of the previous region, to reflect
- // that the def could theoretically have been scheduled at the end.
- DefIndices[Reg] = InsertPosIndex;
- }
-
- PrescanInstruction(MI);
- ScanInstruction(MI, Count);
+ if (AntiDepBreak != NULL)
+ AntiDepBreak->Observe(MI, Count, InsertPosIndex);
}
/// FinishBlock - Clean up register live-range state.
///
void SchedulePostRATDList::FinishBlock() {
- RegRefs.clear();
+ if (AntiDepBreak != NULL)
+ AntiDepBreak->FinishBlock();
// Call the superclass.
ScheduleDAGInstrs::FinishBlock();
}
-/// CriticalPathStep - Return the next SUnit after SU on the bottom-up
-/// critical path.
-static SDep *CriticalPathStep(SUnit *SU) {
- SDep *Next = 0;
- unsigned NextDepth = 0;
- // Find the predecessor edge with the greatest depth.
- for (SUnit::pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
- P != PE; ++P) {
- SUnit *PredSU = P->getSUnit();
- unsigned PredLatency = P->getLatency();
- unsigned PredTotalLatency = PredSU->getDepth() + PredLatency;
- // In the case of a latency tie, prefer an anti-dependency edge over
- // other types of edges.
- if (NextDepth < PredTotalLatency ||
- (NextDepth == PredTotalLatency && P->getKind() == SDep::Anti)) {
- NextDepth = PredTotalLatency;
- Next = &*P;
- }
- }
- return Next;
-}
-
-void SchedulePostRATDList::PrescanInstruction(MachineInstr *MI) {
- // Scan the register operands for this instruction and update
- // Classes and RegRefs.
- for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
- MachineOperand &MO = MI->getOperand(i);
- if (!MO.isReg()) continue;
- unsigned Reg = MO.getReg();
- if (Reg == 0) continue;
- const TargetRegisterClass *NewRC = 0;
-
- if (i < MI->getDesc().getNumOperands())
- NewRC = MI->getDesc().OpInfo[i].getRegClass(TRI);
-
- // For now, only allow the register to be changed if its register
- // class is consistent across all uses.
- if (!Classes[Reg] && NewRC)
- Classes[Reg] = NewRC;
- else if (!NewRC || Classes[Reg] != NewRC)
- Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
-
- // Now check for aliases.
- for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
- // If an alias of the reg is used during the live range, give up.
- // Note that this allows us to skip checking if AntiDepReg
- // overlaps with any of the aliases, among other things.
- unsigned AliasReg = *Alias;
- if (Classes[AliasReg]) {
- Classes[AliasReg] = reinterpret_cast<TargetRegisterClass *>(-1);
- Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
- }
- }
-
- // If we're still willing to consider this register, note the reference.
- if (Classes[Reg] != reinterpret_cast<TargetRegisterClass *>(-1))
- RegRefs.insert(std::make_pair(Reg, &MO));
-
- // It's not safe to change register allocation for source operands of
- // that have special allocation requirements.
- if (MO.isUse() && MI->getDesc().hasExtraSrcRegAllocReq()) {
- if (KeepRegs.insert(Reg)) {
- for (const unsigned *Subreg = TRI->getSubRegisters(Reg);
- *Subreg; ++Subreg)
- KeepRegs.insert(*Subreg);
- }
- }
- }
-}
-
-void SchedulePostRATDList::ScanInstruction(MachineInstr *MI,
- unsigned Count) {
- // Update liveness.
- // Proceding upwards, registers that are defed but not used in this
- // instruction are now dead.
- for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
- MachineOperand &MO = MI->getOperand(i);
- if (!MO.isReg()) continue;
- unsigned Reg = MO.getReg();
- if (Reg == 0) continue;
- if (!MO.isDef()) continue;
- // Ignore two-addr defs.
- if (MI->isRegTiedToUseOperand(i)) continue;
-
- DefIndices[Reg] = Count;
- KillIndices[Reg] = ~0u;
- assert(((KillIndices[Reg] == ~0u) !=
- (DefIndices[Reg] == ~0u)) &&
- "Kill and Def maps aren't consistent for Reg!");
- KeepRegs.erase(Reg);
- Classes[Reg] = 0;
- RegRefs.erase(Reg);
- // Repeat, for all subregs.
- for (const unsigned *Subreg = TRI->getSubRegisters(Reg);
- *Subreg; ++Subreg) {
- unsigned SubregReg = *Subreg;
- DefIndices[SubregReg] = Count;
- KillIndices[SubregReg] = ~0u;
- KeepRegs.erase(SubregReg);
- Classes[SubregReg] = 0;
- RegRefs.erase(SubregReg);
- }
- // Conservatively mark super-registers as unusable.
- for (const unsigned *Super = TRI->getSuperRegisters(Reg);
- *Super; ++Super) {
- unsigned SuperReg = *Super;
- Classes[SuperReg] = reinterpret_cast<TargetRegisterClass *>(-1);
- }
- }
- for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
- MachineOperand &MO = MI->getOperand(i);
- if (!MO.isReg()) continue;
- unsigned Reg = MO.getReg();
- if (Reg == 0) continue;
- if (!MO.isUse()) continue;
-
- const TargetRegisterClass *NewRC = 0;
- if (i < MI->getDesc().getNumOperands())
- NewRC = MI->getDesc().OpInfo[i].getRegClass(TRI);
-
- // For now, only allow the register to be changed if its register
- // class is consistent across all uses.
- if (!Classes[Reg] && NewRC)
- Classes[Reg] = NewRC;
- else if (!NewRC || Classes[Reg] != NewRC)
- Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
-
- RegRefs.insert(std::make_pair(Reg, &MO));
-
- // It wasn't previously live but now it is, this is a kill.
- if (KillIndices[Reg] == ~0u) {
- KillIndices[Reg] = Count;
- DefIndices[Reg] = ~0u;
- assert(((KillIndices[Reg] == ~0u) !=
- (DefIndices[Reg] == ~0u)) &&
- "Kill and Def maps aren't consistent for Reg!");
- }
- // Repeat, for all aliases.
- for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias) {
- unsigned AliasReg = *Alias;
- if (KillIndices[AliasReg] == ~0u) {
- KillIndices[AliasReg] = Count;
- DefIndices[AliasReg] = ~0u;
- }
- }
- }
-}
-
-unsigned
-SchedulePostRATDList::findSuitableFreeRegister(unsigned AntiDepReg,
- unsigned LastNewReg,
- const TargetRegisterClass *RC) {
- for (TargetRegisterClass::iterator R = RC->allocation_order_begin(MF),
- RE = RC->allocation_order_end(MF); R != RE; ++R) {
- unsigned NewReg = *R;
- // Don't replace a register with itself.
- if (NewReg == AntiDepReg) continue;
- // Don't replace a register with one that was recently used to repair
- // an anti-dependence with this AntiDepReg, because that would
- // re-introduce that anti-dependence.
- if (NewReg == LastNewReg) continue;
- // If NewReg is dead and NewReg's most recent def is not before
- // AntiDepReg's kill, it's safe to replace AntiDepReg with NewReg.
- assert(((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u)) &&
- "Kill and Def maps aren't consistent for AntiDepReg!");
- assert(((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u)) &&
- "Kill and Def maps aren't consistent for NewReg!");
- if (KillIndices[NewReg] != ~0u ||
- Classes[NewReg] == reinterpret_cast<TargetRegisterClass *>(-1) ||
- KillIndices[AntiDepReg] > DefIndices[NewReg])
- continue;
- return NewReg;
- }
-
- // No registers are free and available!
- return 0;
-}
-
-/// BreakAntiDependencies - Identifiy anti-dependencies along the critical path
-/// of the ScheduleDAG and break them by renaming registers.
-///
-bool SchedulePostRATDList::BreakAntiDependencies() {
- // The code below assumes that there is at least one instruction,
- // so just duck out immediately if the block is empty.
- if (SUnits.empty()) return false;
-
- // Find the node at the bottom of the critical path.
- SUnit *Max = 0;
- for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
- SUnit *SU = &SUnits[i];
- if (!Max || SU->getDepth() + SU->Latency > Max->getDepth() + Max->Latency)
- Max = SU;
- }
-
-#ifndef NDEBUG
- {
- DEBUG(errs() << "Critical path has total latency "
- << (Max->getDepth() + Max->Latency) << "\n");
- DEBUG(errs() << "Available regs:");
- for (unsigned Reg = 0; Reg < TRI->getNumRegs(); ++Reg) {
- if (KillIndices[Reg] == ~0u)
- DEBUG(errs() << " " << TRI->getName(Reg));
- }
- DEBUG(errs() << '\n');
- }
-#endif
-
- // Track progress along the critical path through the SUnit graph as we walk
- // the instructions.
- SUnit *CriticalPathSU = Max;
- MachineInstr *CriticalPathMI = CriticalPathSU->getInstr();
-
- // Consider this pattern:
- // A = ...
- // ... = A
- // A = ...
- // ... = A
- // A = ...
- // ... = A
- // A = ...
- // ... = A
- // There are three anti-dependencies here, and without special care,
- // we'd break all of them using the same register:
- // A = ...
- // ... = A
- // B = ...
- // ... = B
- // B = ...
- // ... = B
- // B = ...
- // ... = B
- // because at each anti-dependence, B is the first register that
- // isn't A which is free. This re-introduces anti-dependencies
- // at all but one of the original anti-dependencies that we were
- // trying to break. To avoid this, keep track of the most recent
- // register that each register was replaced with, avoid
- // using it to repair an anti-dependence on the same register.
- // This lets us produce this:
- // A = ...
- // ... = A
- // B = ...
- // ... = B
- // C = ...
- // ... = C
- // B = ...
- // ... = B
- // This still has an anti-dependence on B, but at least it isn't on the
- // original critical path.
- //
- // TODO: If we tracked more than one register here, we could potentially
- // fix that remaining critical edge too. This is a little more involved,
- // because unlike the most recent register, less recent registers should
- // still be considered, though only if no other registers are available.
- unsigned LastNewReg[TargetRegisterInfo::FirstVirtualRegister] = {};
-
- // Attempt to break anti-dependence edges on the critical path. Walk the
- // instructions from the bottom up, tracking information about liveness
- // as we go to help determine which registers are available.
- bool Changed = false;
- unsigned Count = InsertPosIndex - 1;
- for (MachineBasicBlock::iterator I = InsertPos, E = Begin;
- I != E; --Count) {
- MachineInstr *MI = --I;
-
- // Check if this instruction has a dependence on the critical path that
- // is an anti-dependence that we may be able to break. If it is, set
- // AntiDepReg to the non-zero register associated with the anti-dependence.
- //
- // We limit our attention to the critical path as a heuristic to avoid
- // breaking anti-dependence edges that aren't going to significantly
- // impact the overall schedule. There are a limited number of registers
- // and we want to save them for the important edges.
- //
- // TODO: Instructions with multiple defs could have multiple
- // anti-dependencies. The current code here only knows how to break one
- // edge per instruction. Note that we'd have to be able to break all of
- // the anti-dependencies in an instruction in order to be effective.
- unsigned AntiDepReg = 0;
- if (MI == CriticalPathMI) {
- if (SDep *Edge = CriticalPathStep(CriticalPathSU)) {
- SUnit *NextSU = Edge->getSUnit();
-
- // Only consider anti-dependence edges.
- if (Edge->getKind() == SDep::Anti) {
- AntiDepReg = Edge->getReg();
- assert(AntiDepReg != 0 && "Anti-dependence on reg0?");
- if (!AllocatableSet.test(AntiDepReg))
- // Don't break anti-dependencies on non-allocatable registers.
- AntiDepReg = 0;
- else if (KeepRegs.count(AntiDepReg))
- // Don't break anti-dependencies if an use down below requires
- // this exact register.
- AntiDepReg = 0;
- else {
- // If the SUnit has other dependencies on the SUnit that it
- // anti-depends on, don't bother breaking the anti-dependency
- // since those edges would prevent such units from being
- // scheduled past each other regardless.
- //
- // Also, if there are dependencies on other SUnits with the
- // same register as the anti-dependency, don't attempt to
- // break it.
- for (SUnit::pred_iterator P = CriticalPathSU->Preds.begin(),
- PE = CriticalPathSU->Preds.end(); P != PE; ++P)
- if (P->getSUnit() == NextSU ?
- (P->getKind() != SDep::Anti || P->getReg() != AntiDepReg) :
- (P->getKind() == SDep::Data && P->getReg() == AntiDepReg)) {
- AntiDepReg = 0;
- break;
- }
- }
- }
- CriticalPathSU = NextSU;
- CriticalPathMI = CriticalPathSU->getInstr();
- } else {
- // We've reached the end of the critical path.
- CriticalPathSU = 0;
- CriticalPathMI = 0;
- }
- }
-
- PrescanInstruction(MI);
-
- if (MI->getDesc().hasExtraDefRegAllocReq())
- // If this instruction's defs have special allocation requirement, don't
- // break this anti-dependency.
- AntiDepReg = 0;
- else if (AntiDepReg) {
- // If this instruction has a use of AntiDepReg, breaking it
- // is invalid.
- for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
- MachineOperand &MO = MI->getOperand(i);
- if (!MO.isReg()) continue;
- unsigned Reg = MO.getReg();
- if (Reg == 0) continue;
- if (MO.isUse() && AntiDepReg == Reg) {
- AntiDepReg = 0;
- break;
- }
- }
- }
-
- // Determine AntiDepReg's register class, if it is live and is
- // consistently used within a single class.
- const TargetRegisterClass *RC = AntiDepReg != 0 ? Classes[AntiDepReg] : 0;
- assert((AntiDepReg == 0 || RC != NULL) &&
- "Register should be live if it's causing an anti-dependence!");
- if (RC == reinterpret_cast<TargetRegisterClass *>(-1))
- AntiDepReg = 0;
-
- // Look for a suitable register to use to break the anti-depenence.
- //
- // TODO: Instead of picking the first free register, consider which might
- // be the best.
- if (AntiDepReg != 0) {
- if (unsigned NewReg = findSuitableFreeRegister(AntiDepReg,
- LastNewReg[AntiDepReg],
- RC)) {
- DEBUG(errs() << "Breaking anti-dependence edge on "
- << TRI->getName(AntiDepReg)
- << " with " << RegRefs.count(AntiDepReg) << " references"
- << " using " << TRI->getName(NewReg) << "!\n");
-
- // Update the references to the old register to refer to the new
- // register.
- std::pair<std::multimap<unsigned, MachineOperand *>::iterator,
- std::multimap<unsigned, MachineOperand *>::iterator>
- Range = RegRefs.equal_range(AntiDepReg);
- for (std::multimap<unsigned, MachineOperand *>::iterator
- Q = Range.first, QE = Range.second; Q != QE; ++Q)
- Q->second->setReg(NewReg);
-
- // We just went back in time and modified history; the
- // liveness information for the anti-depenence reg is now
- // inconsistent. Set the state as if it were dead.
- Classes[NewReg] = Classes[AntiDepReg];
- DefIndices[NewReg] = DefIndices[AntiDepReg];
- KillIndices[NewReg] = KillIndices[AntiDepReg];
- assert(((KillIndices[NewReg] == ~0u) !=
- (DefIndices[NewReg] == ~0u)) &&
- "Kill and Def maps aren't consistent for NewReg!");
-
- Classes[AntiDepReg] = 0;
- DefIndices[AntiDepReg] = KillIndices[AntiDepReg];
- KillIndices[AntiDepReg] = ~0u;
- assert(((KillIndices[AntiDepReg] == ~0u) !=
- (DefIndices[AntiDepReg] == ~0u)) &&
- "Kill and Def maps aren't consistent for AntiDepReg!");
-
- RegRefs.erase(AntiDepReg);
- Changed = true;
- LastNewReg[AntiDepReg] = NewReg;
- }
- }
-
- ScanInstruction(MI, Count);
- }
-
- return Changed;
-}
-
/// StartBlockForKills - Initialize register live-range state for updating kills
///
void SchedulePostRATDList::StartBlockForKills(MachineBasicBlock *BB) {
Modified: llvm/trunk/lib/Target/ARM/ARMSubtarget.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMSubtarget.h?rev=85127&r1=85126&r2=85127&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMSubtarget.h (original)
+++ llvm/trunk/lib/Target/ARM/ARMSubtarget.h Mon Oct 26 11:59:04 2009
@@ -130,7 +130,7 @@
/// for Thumb1.
bool enablePostRAScheduler(CodeGenOpt::Level OptLevel,
TargetSubtarget::AntiDepBreakMode& mode) const {
- mode = TargetSubtarget::ANTIDEP_NONE;
+ mode = TargetSubtarget::ANTIDEP_CRITICAL;
return PostRAScheduler && OptLevel >= CodeGenOpt::Default;
}
Modified: llvm/trunk/test/CodeGen/X86/break-anti-dependencies.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/break-anti-dependencies.ll?rev=85127&r1=85126&r2=85127&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/break-anti-dependencies.ll (original)
+++ llvm/trunk/test/CodeGen/X86/break-anti-dependencies.ll Mon Oct 26 11:59:04 2009
@@ -1,7 +1,7 @@
-; RUN: llc < %s -march=x86-64 -post-RA-scheduler -break-anti-dependencies=false > %t
+; RUN: llc < %s -march=x86-64 -post-RA-scheduler -break-anti-dependencies=none > %t
; RUN: grep {%xmm0} %t | count 14
; RUN: not grep {%xmm1} %t
-; RUN: llc < %s -march=x86-64 -post-RA-scheduler -break-anti-dependencies > %t
+; RUN: llc < %s -march=x86-64 -post-RA-scheduler -break-anti-dependencies=critical > %t
; RUN: grep {%xmm0} %t | count 7
; RUN: grep {%xmm1} %t | count 7
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