From 82d77e81457ffeaeb2144ab3a08cb3f3e7466eaa Mon Sep 17 00:00:00 2001 From: Jakob Stoklund Olesen Date: Sat, 19 May 2012 05:25:50 +0000 Subject: [PATCH] Run proper recursive dead code elimination during coalescing. Dead copies cause problems because they are trivial to coalesce, but removing them gived the live range a dangling end point. This patch enables full dead code elimination which trims live ranges to their uses so end points don't dangle. DCE may erase multiple instructions. Put the pointers in an ErasedInstrs set so we never risk visiting erased instructions in the work list. There isn't supposed to be any dead copies entering RegisterCoalescer, but they do slip by as evidenced by test/CodeGen/X86/coalescer-dce.ll. llvm-svn: 157101 --- llvm/lib/CodeGen/LiveInterval.cpp | 5 ++- llvm/lib/CodeGen/RegisterCoalescer.cpp | 79 +++++++++++++++++++++++++--------- 2 files changed, 63 insertions(+), 21 deletions(-) diff --git a/llvm/lib/CodeGen/LiveInterval.cpp b/llvm/lib/CodeGen/LiveInterval.cpp index aa44d37..010ef48 100644 --- a/llvm/lib/CodeGen/LiveInterval.cpp +++ b/llvm/lib/CodeGen/LiveInterval.cpp @@ -681,7 +681,10 @@ void ConnectedVNInfoEqClasses::Distribute(LiveInterval *LIV[], SlotIndex Idx = LIS.getInstructionIndex(MI); Idx = Idx.getRegSlot(MO.isUse()); const VNInfo *VNI = LI.getVNInfoAt(Idx); - assert(VNI && "Interval not live at use."); + // FIXME: We should be able to assert(VNI) here, but the coalescer leaves + // dangling defs around. + if (!VNI) + continue; MO.setReg(LIV[getEqClass(VNI)]->reg); } diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp index 8f4a10c..84fd590 100644 --- a/llvm/lib/CodeGen/RegisterCoalescer.cpp +++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp @@ -21,29 +21,30 @@ #include "llvm/Pass.h" #include "llvm/Value.h" +#include "llvm/ADT/OwningPtr.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/CodeGen/LiveIntervalAnalysis.h" -#include "llvm/CodeGen/MachineInstr.h" -#include "llvm/CodeGen/MachineRegisterInfo.h" -#include "llvm/Target/TargetInstrInfo.h" -#include "llvm/Target/TargetRegisterInfo.h" #include "llvm/CodeGen/LiveIntervalAnalysis.h" -#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/CodeGen/LiveRangeEdit.h" #include "llvm/CodeGen/MachineFrameInfo.h" #include "llvm/CodeGen/MachineInstr.h" +#include "llvm/CodeGen/MachineInstr.h" #include "llvm/CodeGen/MachineLoopInfo.h" #include "llvm/CodeGen/MachineRegisterInfo.h" +#include "llvm/CodeGen/MachineRegisterInfo.h" #include "llvm/CodeGen/Passes.h" -#include "llvm/Target/TargetInstrInfo.h" -#include "llvm/Target/TargetMachine.h" -#include "llvm/Target/TargetOptions.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/raw_ostream.h" -#include "llvm/ADT/OwningPtr.h" -#include "llvm/ADT/SmallSet.h" -#include "llvm/ADT/Statistic.h" -#include "llvm/ADT/STLExtras.h" +#include "llvm/Target/TargetInstrInfo.h" +#include "llvm/Target/TargetInstrInfo.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Target/TargetOptions.h" +#include "llvm/Target/TargetRegisterInfo.h" #include #include using namespace llvm; @@ -67,7 +68,8 @@ VerifyCoalescing("verify-coalescing", cl::Hidden); namespace { - class RegisterCoalescer : public MachineFunctionPass { + class RegisterCoalescer : public MachineFunctionPass, + private LiveRangeEdit::Delegate { MachineFunction* MF; MachineRegisterInfo* MRI; const TargetMachine* TM; @@ -83,10 +85,6 @@ namespace { /// SmallPtrSet JoinedCopies; - /// ReMatCopies - Keep track of copies eliminated due to remat. - /// - SmallPtrSet ReMatCopies; - /// ReMatDefs - Keep track of definition instructions which have /// been remat'ed. SmallPtrSet ReMatDefs; @@ -94,6 +92,19 @@ namespace { /// WorkList - Copy instructions yet to be coalesced. SmallVector WorkList; + /// ErasedInstrs - Set of instruction pointers that have been erased, and + /// that may be present in WorkList. + SmallPtrSet ErasedInstrs; + + /// Dead instructions that are about to be deleted. + SmallVector DeadDefs; + + /// Recursively eliminate dead defs in DeadDefs. + void eliminateDeadDefs(); + + /// LiveRangeEdit callback. + void LRE_WillEraseInstruction(MachineInstr *MI); + /// joinAllIntervals - join compatible live intervals void joinAllIntervals(); @@ -383,6 +394,17 @@ void RegisterCoalescer::markAsJoined(MachineInstr *CopyMI) { I->setIsUndef(true); } +void RegisterCoalescer::eliminateDeadDefs() { + SmallVector NewRegs; + LiveRangeEdit(0, NewRegs, *MF, *LIS, 0, this).eliminateDeadDefs(DeadDefs); +} + +// Callback from eliminateDeadDefs(). +void RegisterCoalescer::LRE_WillEraseInstruction(MachineInstr *MI) { + // MI may be in WorkList. Make sure we don't visit it. + ErasedInstrs.insert(MI); +} + /// adjustCopiesBackFrom - We found a non-trivially-coalescable copy with IntA /// being the source and IntB being the dest, thus this defines a value number /// in IntB. If the source value number (in IntA) is defined by a copy from B, @@ -844,7 +866,7 @@ bool RegisterCoalescer::reMaterializeTrivialDef(LiveInterval &SrcInt, } CopyMI->eraseFromParent(); - ReMatCopies.insert(CopyMI); + ErasedInstrs.insert(CopyMI); ReMatDefs.insert(DefMI); DEBUG(dbgs() << "Remat: " << *NewMI); ++NumReMats; @@ -1025,7 +1047,7 @@ bool RegisterCoalescer::canJoinPhys(CoalescerPair &CP) { bool RegisterCoalescer::joinCopy(MachineInstr *CopyMI, bool &Again) { Again = false; - if (JoinedCopies.count(CopyMI) || ReMatCopies.count(CopyMI)) + if (JoinedCopies.count(CopyMI)) return false; // Already done. DEBUG(dbgs() << LIS->getInstructionIndex(CopyMI) << '\t' << *CopyMI); @@ -1036,6 +1058,16 @@ bool RegisterCoalescer::joinCopy(MachineInstr *CopyMI, bool &Again) { return false; } + // Dead code elimination. This really should be handled by MachineDCE, but + // sometimes dead copies slip through, and we can't generate invalid live + // ranges. + if (!CP.isPhys() && CopyMI->allDefsAreDead()) { + DEBUG(dbgs() << "\tCopy is dead.\n"); + DeadDefs.push_back(CopyMI); + eliminateDeadDefs(); + return true; + } + // If they are already joined we continue. if (CP.getSrcReg() == CP.getDstReg()) { markAsJoined(CopyMI); @@ -1542,6 +1574,12 @@ bool RegisterCoalescer::copyCoalesceWorkList(unsigned From) { for (unsigned i = From, e = WorkList.size(); i != e; ++i) { if (!WorkList[i]) continue; + // Skip instruction pointers that have already been erased, for example by + // dead code elimination. + if (ErasedInstrs.erase(WorkList[i])) { + WorkList[i] = 0; + continue; + } bool Again = false; bool Success = joinCopy(WorkList[i], Again); Progress |= Success; @@ -1609,9 +1647,10 @@ void RegisterCoalescer::joinAllIntervals() { void RegisterCoalescer::releaseMemory() { JoinedCopies.clear(); - ReMatCopies.clear(); + ErasedInstrs.clear(); ReMatDefs.clear(); WorkList.clear(); + DeadDefs.clear(); } bool RegisterCoalescer::runOnMachineFunction(MachineFunction &fn) { -- 2.7.4