X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FTwoAddressInstructionPass.cpp;h=f42d47bebda77922bb54ce4ecd3f45915be74e32;hb=50e7ba14ca8ec3a3f4bd6ca0b15dfacfda58ec06;hp=cbe07db3fcbd64d34bbb35d50c9c5bd96c02cd60;hpb=4c57942608094a74543920b7c809e442fa90dd72;p=oota-llvm.git diff --git a/lib/CodeGen/TwoAddressInstructionPass.cpp b/lib/CodeGen/TwoAddressInstructionPass.cpp index cbe07db3fcb..f42d47bebda 100644 --- a/lib/CodeGen/TwoAddressInstructionPass.cpp +++ b/lib/CodeGen/TwoAddressInstructionPass.cpp @@ -27,7 +27,6 @@ // //===----------------------------------------------------------------------===// -#define DEBUG_TYPE "twoaddrinstr" #include "llvm/CodeGen/Passes.h" #include "llvm/ADT/BitVector.h" #include "llvm/ADT/DenseMap.h" @@ -43,14 +42,16 @@ #include "llvm/CodeGen/MachineRegisterInfo.h" #include "llvm/IR/Function.h" #include "llvm/MC/MCInstrItineraries.h" +#include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetMachine.h" -#include "llvm/Target/TargetOptions.h" #include "llvm/Target/TargetRegisterInfo.h" using namespace llvm; +#define DEBUG_TYPE "twoaddrinstr" + STATISTIC(NumTwoAddressInstrs, "Number of two-address instructions"); STATISTIC(NumCommuted , "Number of instructions commuted to coalesce"); STATISTIC(NumAggrCommuted , "Number of instructions aggressively commuted"); @@ -59,6 +60,12 @@ STATISTIC(Num3AddrSunk, "Number of 3-address instructions sunk"); STATISTIC(NumReSchedUps, "Number of instructions re-scheduled up"); STATISTIC(NumReSchedDowns, "Number of instructions re-scheduled down"); +// Temporary flag to disable rescheduling. +static cl::opt +EnableRescheduling("twoaddr-reschedule", + cl::desc("Coalesce copies by rescheduling (default=true)"), + cl::init(true), cl::Hidden); + namespace { class TwoAddressInstructionPass : public MachineFunctionPass { MachineFunction *MF; @@ -120,7 +127,7 @@ class TwoAddressInstructionPass : public MachineFunctionPass { bool tryInstructionTransform(MachineBasicBlock::iterator &mi, MachineBasicBlock::iterator &nmi, unsigned SrcIdx, unsigned DstIdx, - unsigned Dist); + unsigned Dist, bool shouldOnlyCommute); void scanUses(unsigned DstReg); @@ -138,7 +145,7 @@ public: initializeTwoAddressInstructionPassPass(*PassRegistry::getPassRegistry()); } - virtual void getAnalysisUsage(AnalysisUsage &AU) const { + void getAnalysisUsage(AnalysisUsage &AU) const override { AU.setPreservesCFG(); AU.addRequired(); AU.addPreserved(); @@ -150,7 +157,7 @@ public: } /// runOnMachineFunction - Pass entry point. - bool runOnMachineFunction(MachineFunction&); + bool runOnMachineFunction(MachineFunction&) override; }; } // end anonymous namespace @@ -205,7 +212,7 @@ sink3AddrInstruction(MachineInstr *MI, unsigned SavedReg, } // Find the instruction that kills SavedReg. - MachineInstr *KillMI = NULL; + MachineInstr *KillMI = nullptr; if (LIS) { LiveInterval &LI = LIS->getInterval(SavedReg); assert(LI.end() != LI.begin() && @@ -223,7 +230,7 @@ sink3AddrInstruction(MachineInstr *MI, unsigned SavedReg, for (MachineRegisterInfo::use_nodbg_iterator UI = MRI->use_nodbg_begin(SavedReg), UE = MRI->use_nodbg_end(); UI != UE; ++UI) { - MachineOperand &UseMO = UI.getOperand(); + MachineOperand &UseMO = *UI; if (!UseMO.isKill()) continue; KillMI = UseMO.getParent(); @@ -244,12 +251,12 @@ sink3AddrInstruction(MachineInstr *MI, unsigned SavedReg, // FIXME: This can be sped up if there is an easy way to query whether an // instruction is before or after another instruction. Then we can use // MachineRegisterInfo def / use instead. - MachineOperand *KillMO = NULL; + MachineOperand *KillMO = nullptr; MachineBasicBlock::iterator KillPos = KillMI; ++KillPos; unsigned NumVisited = 0; - for (MachineBasicBlock::iterator I = llvm::next(OldPos); I != KillPos; ++I) { + for (MachineBasicBlock::iterator I = std::next(OldPos); I != KillPos; ++I) { MachineInstr *OtherMI = I; // DBG_VALUE cannot be counted against the limit. if (OtherMI->isDebugValue()) @@ -309,9 +316,7 @@ bool TwoAddressInstructionPass::noUseAfterLastDef(unsigned Reg, unsigned Dist, unsigned &LastDef) { LastDef = 0; unsigned LastUse = Dist; - for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(Reg), - E = MRI->reg_end(); I != E; ++I) { - MachineOperand &MO = I.getOperand(); + for (MachineOperand &MO : MRI->reg_operands(Reg)) { MachineInstr *MI = MO.getParent(); if (MI->getParent() != MBB || MI->isDebugValue()) continue; @@ -370,7 +375,7 @@ static bool isPlainlyKilled(MachineInstr *MI, unsigned Reg, SlotIndex useIdx = LIS->getInstructionIndex(MI); LiveInterval::const_iterator I = LI.find(useIdx); assert(I != LI.end() && "Reg must be live-in to use."); - return SlotIndex::isSameInstr(I->end, useIdx); + return !I->end.isBlock() && SlotIndex::isSameInstr(I->end, useIdx); } return MI->killsRegister(Reg); @@ -411,9 +416,9 @@ static bool isKilled(MachineInstr &MI, unsigned Reg, MachineRegisterInfo::def_iterator Begin = MRI->def_begin(Reg); // If there are multiple defs, we can't do a simple analysis, so just // go with what the kill flag says. - if (llvm::next(Begin) != MRI->def_end()) + if (std::next(Begin) != MRI->def_end()) return true; - DefMI = &*Begin; + DefMI = Begin->getParent(); bool IsSrcPhys, IsDstPhys; unsigned SrcReg, DstReg; // If the def is something other than a copy, then it isn't going to @@ -427,10 +432,7 @@ static bool isKilled(MachineInstr &MI, unsigned Reg, /// isTwoAddrUse - Return true if the specified MI uses the specified register /// as a two-address use. If so, return the destination register by reference. static bool isTwoAddrUse(MachineInstr &MI, unsigned Reg, unsigned &DstReg) { - const MCInstrDesc &MCID = MI.getDesc(); - unsigned NumOps = MI.isInlineAsm() - ? MI.getNumOperands() : MCID.getNumOperands(); - for (unsigned i = 0; i != NumOps; ++i) { + for (unsigned i = 0, NumOps = MI.getNumOperands(); i != NumOps; ++i) { const MachineOperand &MO = MI.getOperand(i); if (!MO.isReg() || !MO.isUse() || MO.getReg() != Reg) continue; @@ -453,10 +455,10 @@ MachineInstr *findOnlyInterestingUse(unsigned Reg, MachineBasicBlock *MBB, unsigned &DstReg, bool &IsDstPhys) { if (!MRI->hasOneNonDBGUse(Reg)) // None or more than one use. - return 0; - MachineInstr &UseMI = *MRI->use_nodbg_begin(Reg); + return nullptr; + MachineInstr &UseMI = *MRI->use_instr_nodbg_begin(Reg); if (UseMI.getParent() != MBB) - return 0; + return nullptr; unsigned SrcReg; bool IsSrcPhys; if (isCopyToReg(UseMI, TII, SrcReg, DstReg, IsSrcPhys, IsDstPhys)) { @@ -468,7 +470,7 @@ MachineInstr *findOnlyInterestingUse(unsigned Reg, MachineBasicBlock *MBB, IsDstPhys = TargetRegisterInfo::isPhysicalRegister(DstReg); return &UseMI; } - return 0; + return nullptr; } /// getMappedReg - Return the physical register the specified virtual register @@ -575,25 +577,15 @@ commuteInstruction(MachineBasicBlock::iterator &mi, DEBUG(dbgs() << "2addr: COMMUTING : " << *MI); MachineInstr *NewMI = TII->commuteInstruction(MI); - if (NewMI == 0) { + if (NewMI == nullptr) { DEBUG(dbgs() << "2addr: COMMUTING FAILED!\n"); return false; } DEBUG(dbgs() << "2addr: COMMUTED TO: " << *NewMI); - // If the instruction changed to commute it, update livevar. - if (NewMI != MI) { - if (LV) - // Update live variables - LV->replaceKillInstruction(RegC, MI, NewMI); - if (LIS) - LIS->ReplaceMachineInstrInMaps(MI, NewMI); - - MBB->insert(mi, NewMI); // Insert the new inst - MBB->erase(mi); // Nuke the old inst. - mi = NewMI; - DistanceMap.insert(std::make_pair(NewMI, Dist)); - } + assert(NewMI == MI && + "TargetInstrInfo::commuteInstruction() should not return a new " + "instruction unless it was requested."); // Update source register map. unsigned FromRegC = getMappedReg(RegC, SrcRegMap); @@ -654,7 +646,7 @@ TwoAddressInstructionPass::convertInstTo3Addr(MachineBasicBlock::iterator &mi, if (!Sunk) { DistanceMap.insert(std::make_pair(NewMI, Dist)); mi = NewMI; - nmi = llvm::next(mi); + nmi = std::next(mi); } // Update source and destination register maps. @@ -764,7 +756,7 @@ rescheduleMIBelowKill(MachineBasicBlock::iterator &mi, // Must be created from unfolded load. Don't waste time trying this. return false; - MachineInstr *KillMI = 0; + MachineInstr *KillMI = nullptr; if (LIS) { LiveInterval &LI = LIS->getInterval(Reg); assert(LI.end() != LI.begin() && @@ -823,7 +815,7 @@ rescheduleMIBelowKill(MachineBasicBlock::iterator &mi, // Move the copies connected to MI down as well. MachineBasicBlock::iterator Begin = MI; - MachineBasicBlock::iterator AfterMI = llvm::next(Begin); + MachineBasicBlock::iterator AfterMI = std::next(Begin); MachineBasicBlock::iterator End = AfterMI; while (End->isCopy() && Defs.count(End->getOperand(1).getReg())) { @@ -883,7 +875,7 @@ rescheduleMIBelowKill(MachineBasicBlock::iterator &mi, } // Move debug info as well. - while (Begin != MBB->begin() && llvm::prior(Begin)->isDebugValue()) + while (Begin != MBB->begin() && std::prev(Begin)->isDebugValue()) --Begin; nmi = End; @@ -898,7 +890,7 @@ rescheduleMIBelowKill(MachineBasicBlock::iterator &mi, LIS->handleMove(CopyMI); InsertPos = CopyMI; } - End = llvm::next(MachineBasicBlock::iterator(MI)); + End = std::next(MachineBasicBlock::iterator(MI)); } // Copies following MI may have been moved as well. @@ -921,19 +913,17 @@ rescheduleMIBelowKill(MachineBasicBlock::iterator &mi, /// instruction too close to the defs of its register dependencies. bool TwoAddressInstructionPass::isDefTooClose(unsigned Reg, unsigned Dist, MachineInstr *MI) { - for (MachineRegisterInfo::def_iterator DI = MRI->def_begin(Reg), - DE = MRI->def_end(); DI != DE; ++DI) { - MachineInstr *DefMI = &*DI; - if (DefMI->getParent() != MBB || DefMI->isCopy() || DefMI->isCopyLike()) + for (MachineInstr &DefMI : MRI->def_instructions(Reg)) { + if (DefMI.getParent() != MBB || DefMI.isCopy() || DefMI.isCopyLike()) continue; - if (DefMI == MI) + if (&DefMI == MI) return true; // MI is defining something KillMI uses - DenseMap::iterator DDI = DistanceMap.find(DefMI); + DenseMap::iterator DDI = DistanceMap.find(&DefMI); if (DDI == DistanceMap.end()) return true; // Below MI unsigned DefDist = DDI->second; assert(Dist > DefDist && "Visited def already?"); - if (TII->getInstrLatency(InstrItins, DefMI) > (Dist - DefDist)) + if (TII->getInstrLatency(InstrItins, &DefMI) > (Dist - DefDist)) return true; } return false; @@ -958,7 +948,7 @@ rescheduleKillAboveMI(MachineBasicBlock::iterator &mi, // Must be created from unfolded load. Don't waste time trying this. return false; - MachineInstr *KillMI = 0; + MachineInstr *KillMI = nullptr; if (LIS) { LiveInterval &LI = LIS->getInterval(Reg); assert(LI.end() != LI.begin() && @@ -1067,15 +1057,15 @@ rescheduleKillAboveMI(MachineBasicBlock::iterator &mi, // Move the old kill above MI, don't forget to move debug info as well. MachineBasicBlock::iterator InsertPos = mi; - while (InsertPos != MBB->begin() && llvm::prior(InsertPos)->isDebugValue()) + while (InsertPos != MBB->begin() && std::prev(InsertPos)->isDebugValue()) --InsertPos; MachineBasicBlock::iterator From = KillMI; - MachineBasicBlock::iterator To = llvm::next(From); - while (llvm::prior(From)->isDebugValue()) + MachineBasicBlock::iterator To = std::next(From); + while (std::prev(From)->isDebugValue()) --From; MBB->splice(InsertPos, MBB, From, To); - nmi = llvm::prior(InsertPos); // Backtrack so we process the moved instr. + nmi = std::prev(InsertPos); // Backtrack so we process the moved instr. DistanceMap.erase(DI); // Update live variables @@ -1095,11 +1085,13 @@ rescheduleKillAboveMI(MachineBasicBlock::iterator &mi, /// either eliminate the tied operands or improve the opportunities for /// coalescing away the register copy. Returns true if no copy needs to be /// inserted to untie mi's operands (either because they were untied, or -/// because mi was rescheduled, and will be visited again later). +/// because mi was rescheduled, and will be visited again later). If the +/// shouldOnlyCommute flag is true, only instruction commutation is attempted. bool TwoAddressInstructionPass:: tryInstructionTransform(MachineBasicBlock::iterator &mi, MachineBasicBlock::iterator &nmi, - unsigned SrcIdx, unsigned DstIdx, unsigned Dist) { + unsigned SrcIdx, unsigned DstIdx, + unsigned Dist, bool shouldOnlyCommute) { if (OptLevel == CodeGenOpt::None) return false; @@ -1148,9 +1140,12 @@ tryInstructionTransform(MachineBasicBlock::iterator &mi, return false; } + if (shouldOnlyCommute) + return false; + // If there is one more use of regB later in the same MBB, consider // re-schedule this MI below it. - if (rescheduleMIBelowKill(mi, nmi, regB)) { + if (EnableRescheduling && rescheduleMIBelowKill(mi, nmi, regB)) { ++NumReSchedDowns; return true; } @@ -1169,7 +1164,7 @@ tryInstructionTransform(MachineBasicBlock::iterator &mi, // If there is one more use of regB later in the same MBB, consider // re-schedule it before this MI if it's legal. - if (rescheduleKillAboveMI(mi, nmi, regB)) { + if (EnableRescheduling && rescheduleKillAboveMI(mi, nmi, regB)) { ++NumReSchedUps; return true; } @@ -1223,10 +1218,12 @@ tryInstructionTransform(MachineBasicBlock::iterator &mi, unsigned NewDstIdx = NewMIs[1]->findRegisterDefOperandIdx(regA); unsigned NewSrcIdx = NewMIs[1]->findRegisterUseOperandIdx(regB); MachineBasicBlock::iterator NewMI = NewMIs[1]; - bool TransformSuccess = - tryInstructionTransform(NewMI, mi, NewSrcIdx, NewDstIdx, Dist); - if (TransformSuccess || - NewMIs[1]->getOperand(NewSrcIdx).isKill()) { + bool TransformResult = + tryInstructionTransform(NewMI, mi, NewSrcIdx, NewDstIdx, Dist, true); + (void)TransformResult; + assert(!TransformResult && + "tryInstructionTransform() should return false."); + if (NewMIs[1]->getOperand(NewSrcIdx).isKill()) { // Success, or at least we made an improvement. Keep the unfolded // instructions and discard the original. if (LV) { @@ -1277,8 +1274,6 @@ tryInstructionTransform(MachineBasicBlock::iterator &mi, } mi = NewMIs[1]; - if (TransformSuccess) - return true; } else { // Transforming didn't eliminate the tie and didn't lead to an // improvement. Clean up the unfolded instructions and keep the @@ -1319,13 +1314,14 @@ collectTiedOperands(MachineInstr *MI, TiedOperandMap &TiedOperands) { assert(SrcReg && SrcMO.isUse() && "two address instruction invalid"); // Deal with uses immediately - simply rewrite the src operand. - if (SrcMO.isUndef()) { + if (SrcMO.isUndef() && !DstMO.getSubReg()) { // Constrain the DstReg register class if required. if (TargetRegisterInfo::isVirtualRegister(DstReg)) if (const TargetRegisterClass *RC = TII->getRegClass(MCID, SrcIdx, TRI, *MF)) MRI->constrainRegClass(DstReg, RC); SrcMO.setReg(DstReg); + SrcMO.setSubReg(0); DEBUG(dbgs() << "\t\trewrite undef:\t" << *MI); continue; } @@ -1351,6 +1347,7 @@ TwoAddressInstructionPass::processTiedPairs(MachineInstr *MI, unsigned LastCopiedReg = 0; SlotIndex LastCopyIdx; unsigned RegB = 0; + unsigned SubRegB = 0; for (unsigned tpi = 0, tpe = TiedPairs.size(); tpi != tpe; ++tpi) { unsigned SrcIdx = TiedPairs[tpi].first; unsigned DstIdx = TiedPairs[tpi].second; @@ -1361,6 +1358,7 @@ TwoAddressInstructionPass::processTiedPairs(MachineInstr *MI, // Grab RegB from the instruction because it may have changed if the // instruction was commuted. RegB = MI->getOperand(SrcIdx).getReg(); + SubRegB = MI->getOperand(SrcIdx).getSubReg(); if (RegA == RegB) { // The register is tied to multiple destinations (or else we would @@ -1385,8 +1383,25 @@ TwoAddressInstructionPass::processTiedPairs(MachineInstr *MI, #endif // Emit a copy. - BuildMI(*MI->getParent(), MI, MI->getDebugLoc(), - TII->get(TargetOpcode::COPY), RegA).addReg(RegB); + MachineInstrBuilder MIB = BuildMI(*MI->getParent(), MI, MI->getDebugLoc(), + TII->get(TargetOpcode::COPY), RegA); + // If this operand is folding a truncation, the truncation now moves to the + // copy so that the register classes remain valid for the operands. + MIB.addReg(RegB, 0, SubRegB); + const TargetRegisterClass *RC = MRI->getRegClass(RegB); + if (SubRegB) { + if (TargetRegisterInfo::isVirtualRegister(RegA)) { + assert(TRI->getMatchingSuperRegClass(RC, MRI->getRegClass(RegA), + SubRegB) && + "tied subregister must be a truncation"); + // The superreg class will not be used to constrain the subreg class. + RC = nullptr; + } + else { + assert(TRI->getMatchingSuperReg(RegA, SubRegB, MRI->getRegClass(RegB)) + && "tied subregister must be a truncation"); + } + } // Update DistanceMap. MachineBasicBlock::iterator PrevMI = MI; @@ -1402,11 +1417,11 @@ TwoAddressInstructionPass::processTiedPairs(MachineInstr *MI, VNInfo *VNI = LI.getNextValue(LastCopyIdx, LIS->getVNInfoAllocator()); SlotIndex endIdx = LIS->getInstructionIndex(MI).getRegSlot(IsEarlyClobber); - LI.addRange(LiveRange(LastCopyIdx, endIdx, VNI)); + LI.addSegment(LiveInterval::Segment(LastCopyIdx, endIdx, VNI)); } } - DEBUG(dbgs() << "\t\tprepend:\t" << *PrevMI); + DEBUG(dbgs() << "\t\tprepend:\t" << *MIB); MachineOperand &MO = MI->getOperand(SrcIdx); assert(MO.isReg() && MO.getReg() == RegB && MO.isUse() && @@ -1419,9 +1434,12 @@ TwoAddressInstructionPass::processTiedPairs(MachineInstr *MI, // Make sure regA is a legal regclass for the SrcIdx operand. if (TargetRegisterInfo::isVirtualRegister(RegA) && TargetRegisterInfo::isVirtualRegister(RegB)) - MRI->constrainRegClass(RegA, MRI->getRegClass(RegB)); - + MRI->constrainRegClass(RegA, RC); MO.setReg(RegA); + // The getMatchingSuper asserts guarantee that the register class projected + // by SubRegB is compatible with RegA with no subregister. So regardless of + // whether the dest oper writes a subreg, the source oper should not. + MO.setSubReg(0); // Propagate SrcRegMap. SrcRegMap[RegA] = RegB; @@ -1433,12 +1451,14 @@ TwoAddressInstructionPass::processTiedPairs(MachineInstr *MI, // Replace other (un-tied) uses of regB with LastCopiedReg. for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { MachineOperand &MO = MI->getOperand(i); - if (MO.isReg() && MO.getReg() == RegB && MO.isUse()) { + if (MO.isReg() && MO.getReg() == RegB && MO.getSubReg() == SubRegB && + MO.isUse()) { if (MO.isKill()) { MO.setIsKill(false); RemovedKillFlag = true; } MO.setReg(LastCopiedReg); + MO.setSubReg(0); } } } @@ -1459,7 +1479,7 @@ TwoAddressInstructionPass::processTiedPairs(MachineInstr *MI, SlotIndex UseIdx = MIIdx.getRegSlot(IsEarlyClobber); if (I->end == UseIdx) - LI.removeRange(LastCopyIdx, UseIdx); + LI.removeSegment(LastCopyIdx, UseIdx); } } else if (RemovedKillFlag) { @@ -1511,7 +1531,7 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &Func) { Processed.clear(); for (MachineBasicBlock::iterator mi = MBB->begin(), me = MBB->end(); mi != me; ) { - MachineBasicBlock::iterator nmi = llvm::next(mi); + MachineBasicBlock::iterator nmi = std::next(mi); if (mi->isDebugValue()) { mi = nmi; continue; @@ -1541,7 +1561,7 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &Func) { // transformations that may either eliminate the tied operands or // improve the opportunities for coalescing away the register copy. if (TiedOperands.size() == 1) { - SmallVector, 4> &TiedPairs + SmallVectorImpl > &TiedPairs = TiedOperands.begin()->second; if (TiedPairs.size() == 1) { unsigned SrcIdx = TiedPairs[0].first; @@ -1549,7 +1569,7 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &Func) { unsigned SrcReg = mi->getOperand(SrcIdx).getReg(); unsigned DstReg = mi->getOperand(DstIdx).getReg(); if (SrcReg != DstReg && - tryInstructionTransform(mi, nmi, SrcIdx, DstIdx, Dist)) { + tryInstructionTransform(mi, nmi, SrcIdx, DstIdx, Dist, false)) { // The tied operands have been eliminated or shifted further down the // block to ease elimination. Continue processing with 'nmi'. TiedOperands.clear(); @@ -1612,7 +1632,7 @@ eliminateRegSequence(MachineBasicBlock::iterator &MBBI) { TargetRegisterInfo::isPhysicalRegister(DstReg) || !(MI->getNumOperands() & 1)) { DEBUG(dbgs() << "Illegal REG_SEQUENCE instruction:" << *MI); - llvm_unreachable(0); + llvm_unreachable(nullptr); } SmallVector OrigRegs; @@ -1666,7 +1686,7 @@ eliminateRegSequence(MachineBasicBlock::iterator &MBBI) { } MachineBasicBlock::iterator EndMBBI = - llvm::next(MachineBasicBlock::iterator(MI)); + std::next(MachineBasicBlock::iterator(MI)); if (!DefEmitted) { DEBUG(dbgs() << "Turned: " << *MI << " into an IMPLICIT_DEF");