From 8593e418555fdae21a070357fd8734b4069c17d0 Mon Sep 17 00:00:00 2001 From: Dale Johannesen Date: Sun, 29 Apr 2007 19:19:30 +0000 Subject: [PATCH] Rewrite of Thumb constant islands handling (exact allowance for padding around islands and jump tables). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36573 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/ARM/ARMConstantIslandPass.cpp | 306 ++++++++++++++++------- lib/Target/ARM/ARMInstrInfo.cpp | 7 +- 2 files changed, 226 insertions(+), 87 deletions(-) diff --git a/lib/Target/ARM/ARMConstantIslandPass.cpp b/lib/Target/ARM/ARMConstantIslandPass.cpp index ba74c115524..9237228a91c 100644 --- a/lib/Target/ARM/ARMConstantIslandPass.cpp +++ b/lib/Target/ARM/ARMConstantIslandPass.cpp @@ -51,10 +51,14 @@ namespace { unsigned NextUID; /// BBSizes - The size of each MachineBasicBlock in bytes of code, indexed - /// by MBB Number. + /// by MBB Number. The two-byte pads required for Thumb alignment are + /// counted as part of the following block (i.e., the offset and size for + /// a padded block will both be ==2 mod 4). std::vector BBSizes; /// BBOffsets - the offset of each MBB in bytes, starting from 0. + /// The two-byte pads required for Thumb alignment are counted as part of + /// the following block. std::vector BBOffsets; /// WaterList - A sorted list of basic blocks where islands could be placed @@ -121,6 +125,7 @@ namespace { bool HasFarJump; const TargetInstrInfo *TII; + ARMFunctionInfo *AFI; bool isThumb; public: virtual bool runOnMachineFunction(MachineFunction &Fn); @@ -140,8 +145,10 @@ namespace { void AdjustBBOffsetsAfter(MachineBasicBlock *BB, int delta); bool DecrementOldEntry(unsigned CPI, MachineInstr* CPEMI); int LookForExistingCPEntry(CPUser& U, unsigned UserOffset); - bool LookForWater(CPUser&U, unsigned UserOffset, bool* PadNewWater, + bool LookForWater(CPUser&U, unsigned UserOffset, MachineBasicBlock** NewMBB); + MachineBasicBlock* AcceptWater(MachineBasicBlock *WaterBB, + std::vector::iterator IP); void CreateNewWater(unsigned CPUserIndex, unsigned UserOffset, MachineBasicBlock** NewMBB); bool HandleConstantPoolUser(MachineFunction &Fn, unsigned CPUserIndex); @@ -161,9 +168,38 @@ namespace { bool UndoLRSpillRestore(); unsigned GetOffsetOf(MachineInstr *MI) const; + void dumpBBs(); + void verify(MachineFunction &Fn); }; } +/// verify - check BBOffsets, BBSizes, alignment of islands +void ARMConstantIslands::verify(MachineFunction &Fn) { + assert(BBOffsets.size() == BBSizes.size()); + for (unsigned i = 1, e = BBOffsets.size(); i != e; ++i) + assert(BBOffsets[i-1]+BBSizes[i-1] == BBOffsets[i]); + if (isThumb) { + for (MachineFunction::iterator MBBI = Fn.begin(), E = Fn.end(); + MBBI != E; ++MBBI) { + MachineBasicBlock *MBB = MBBI; + if (!MBB->empty() && + MBB->begin()->getOpcode() == ARM::CONSTPOOL_ENTRY) + assert((BBOffsets[MBB->getNumber()]%4 == 0 && + BBSizes[MBB->getNumber()]%4 == 0) || + (BBOffsets[MBB->getNumber()]%4 != 0 && + BBSizes[MBB->getNumber()]%4 != 0)); + } + } +} + +/// print block size and offset information - debugging +void ARMConstantIslands::dumpBBs() { + for (unsigned J = 0, E = BBOffsets.size(); J !=E; ++J) { + DOUT << "block" << J << " offset" << BBOffsets[J] << + " size" << BBSizes[J] << "\n"; + } +} + /// createARMConstantIslandPass - returns an instance of the constpool /// island pass. FunctionPass *llvm::createARMConstantIslandPass() { @@ -172,9 +208,9 @@ FunctionPass *llvm::createARMConstantIslandPass() { bool ARMConstantIslands::runOnMachineFunction(MachineFunction &Fn) { MachineConstantPool &MCP = *Fn.getConstantPool(); - ARMFunctionInfo *AFI = Fn.getInfo(); TII = Fn.getTarget().getInstrInfo(); + AFI = Fn.getInfo(); isThumb = AFI->isThumbFunction(); HasFarJump = false; @@ -215,13 +251,18 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &Fn) { bool Change = false; for (unsigned i = 0, e = CPUsers.size(); i != e; ++i) Change |= HandleConstantPoolUser(Fn, i); + DEBUG(dumpBBs()); for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i) Change |= FixUpImmediateBr(Fn, ImmBranches[i]); + DEBUG(dumpBBs()); if (!Change) break; MadeChange = true; } + // After a while, this might be made debug-only, but it is not expensive. + verify(Fn); + // If LR has been forced spilled and no far jumps (i.e. BL) has been issued. // Undo the spill / restore of LR if possible. if (!HasFarJump && AFI->isLRSpilledForFarJump() && isThumb) @@ -332,8 +373,15 @@ void ARMConstantIslands::InitialFunctionScan(MachineFunction &Fn, unsigned Scale = 1; int UOpc = Opc; switch (Opc) { + case ARM::tBR_JTr: + // A Thumb table jump may involve padding; for the offsets to + // be right, functions containing these must be 4-byte aligned. + AFI->setAlign(2U); + if ((Offset+MBBSize)%4 != 0) + MBBSize += 2; // padding + continue; // Does not get an entry in ImmBranches default: - continue; // Ignore JT branches + continue; // Ignore other JT branches case ARM::Bcc: isCond = true; UOpc = ARM::B; @@ -431,12 +479,12 @@ void ARMConstantIslands::InitialFunctionScan(MachineFunction &Fn, } } - // In thumb mode, if this block is a constpool island, pessimistically - // assume it needs to be padded by two byte so it's aligned on 4 byte - // boundary. + // In thumb mode, if this block is a constpool island, we may need padding + // so it's aligned on 4 byte boundary. if (isThumb && !MBB.empty() && - MBB.begin()->getOpcode() == ARM::CONSTPOOL_ENTRY) + MBB.begin()->getOpcode() == ARM::CONSTPOOL_ENTRY && + (Offset%4) != 0) MBBSize += 2; BBSizes.push_back(MBBSize); @@ -456,6 +504,13 @@ unsigned ARMConstantIslands::GetOffsetOf(MachineInstr *MI) const { // it is in. unsigned Offset = BBOffsets[MBB->getNumber()]; + // If we're looking for a CONSTPOOL_ENTRY in Thumb, see if this block has + // alignment padding, and compensate if so. + if (isThumb && + MI->getOpcode() == ARM::CONSTPOOL_ENTRY && + Offset%4 != 0) + Offset += 2; + // Sum instructions before MI in MBB. for (MachineBasicBlock::iterator I = MBB->begin(); ; ++I) { assert(I != MBB->end() && "Didn't find MI in its own basic block?"); @@ -553,7 +608,8 @@ MachineBasicBlock *ARMConstantIslands::SplitBlockBeforeInstr(MachineInstr *MI) { else WaterList.insert(IP, OrigBB); - // Figure out how large the first NewMBB is. + // Figure out how large the first NewMBB is. (It cannot + // contain a constpool_entry or tablejump.) unsigned NewBBSize = 0; for (MachineBasicBlock::iterator I = NewBB->begin(), E = NewBB->end(); I != E; ++I) @@ -578,10 +634,21 @@ MachineBasicBlock *ARMConstantIslands::SplitBlockBeforeInstr(MachineInstr *MI) { return NewBB; } -/// OffsetIsInRange - Checks whether UserOffset is within MaxDisp of -/// TrialOffset. +/// OffsetIsInRange - Checks whether UserOffset (the location of a constant pool +/// reference) is within MaxDisp of TrialOffset (a proposed location of a +/// constant pool entry). bool ARMConstantIslands::OffsetIsInRange(unsigned UserOffset, unsigned TrialOffset, unsigned MaxDisp, bool NegativeOK) { + // On Thumb offsets==2 mod 4 are rounded down by the hardware for + // purposes of the displacement computation; compensate for that here. + // Effectively, the valid range of displacements is 2 bytes smaller for such + // references. + if (isThumb && UserOffset%4 !=0) + UserOffset -= 2; + // CPEs will be rounded up to a multiple of 4. + if (isThumb && TrialOffset%4 != 0) + TrialOffset += 2; + if (UserOffset <= TrialOffset) { // User before the Trial. if (TrialOffset-UserOffset <= MaxDisp) @@ -599,19 +666,15 @@ bool ARMConstantIslands::OffsetIsInRange(unsigned UserOffset, bool ARMConstantIslands::WaterIsInRange(unsigned UserOffset, MachineBasicBlock* Water, unsigned MaxDisp) { + MachineFunction::iterator I = next(MachineFunction::iterator(Water)); unsigned CPEOffset = BBOffsets[Water->getNumber()] + BBSizes[Water->getNumber()]; - // If the Water is a constpool island, it has already been aligned. - // If not, align it. - if (isThumb && - (Water->empty() || - Water->begin()->getOpcode() != ARM::CONSTPOOL_ENTRY)) - CPEOffset += 2; // If the CPE is to be inserted before the instruction, that will raise - // the offset of the instruction. + // the offset of the instruction. (Currently applies only to ARM, so + // no alignment compensation attempted here.) if (CPEOffset < UserOffset) - UserOffset += isThumb ? 2 : 4; + UserOffset += 4; return OffsetIsInRange (UserOffset, CPEOffset, MaxDisp, !isThumb); } @@ -621,10 +684,8 @@ bool ARMConstantIslands::WaterIsInRange(unsigned UserOffset, bool ARMConstantIslands::CPEIsInRange(MachineInstr *MI, unsigned UserOffset, MachineInstr *CPEMI, unsigned MaxDisp, bool DoDump) { - // In thumb mode, pessimistically assumes the .align 2 before the first CPE - // in the island adds two byte padding. - unsigned AlignAdj = isThumb ? 2 : 0; - unsigned CPEOffset = GetOffsetOf(CPEMI) + AlignAdj; + unsigned CPEOffset = GetOffsetOf(CPEMI); + assert(CPEOffset%4 == 0 && "Misaligned CPE"); if (DoDump) { DOUT << "User of CPE#" << CPEMI->getOperand(0).getImm() @@ -651,11 +712,56 @@ static bool BBIsJumpedOver(MachineBasicBlock *MBB) { return false; } -void ARMConstantIslands::AdjustBBOffsetsAfter(MachineBasicBlock *BB, int delta) -{ - MachineFunction::iterator MBBI = BB->getParent()->end(); - for(unsigned i=BB->getNumber()+1; igetParent()->getNumBlockIDs(); i++) +void ARMConstantIslands::AdjustBBOffsetsAfter(MachineBasicBlock *BB, + int delta) { + MachineFunction::iterator MBBI = BB; MBBI = next(MBBI); + for(unsigned i=BB->getNumber()+1; igetParent()->getNumBlockIDs(); i++) { BBOffsets[i] += delta; + // If some existing blocks have padding, adjust the padding as needed, a + // bit tricky. delta can be negative so don't use % on that. + if (isThumb) { + MachineBasicBlock *MBB = MBBI; + if (!MBB->empty()) { + // Constant pool entries require padding. + if (MBB->begin()->getOpcode() == ARM::CONSTPOOL_ENTRY) { + unsigned oldOffset = BBOffsets[i] - delta; + if (oldOffset%4==0 && BBOffsets[i]%4!=0) { + // add new padding + BBSizes[i] += 2; + delta += 2; + } else if (oldOffset%4!=0 && BBOffsets[i]%4==0) { + // remove existing padding + BBSizes[i] -=2; + delta -= 2; + } + } + // Thumb jump tables require padding. They can be at the end, or + // followed by an unconditional branch. + MachineInstr *ThumbJTMI = NULL; + if (prior(MBB->end())->getOpcode() == ARM::tBR_JTr) + ThumbJTMI = prior(MBB->end()); + else if (prior(MBB->end()) != MBB->begin() && + prior(prior(MBB->end()))->getOpcode() == ARM::tBR_JTr) + ThumbJTMI = prior(prior(MBB->end())); + if (ThumbJTMI) { + unsigned newMIOffset = GetOffsetOf(ThumbJTMI); + unsigned oldMIOffset = newMIOffset - delta; + if (oldMIOffset%4 == 0 && newMIOffset%4 != 0) { + // remove existing padding + BBSizes[i] -= 2; + delta -= 2; + } else if (oldMIOffset%4 != 0 && newMIOffset%4 == 0) { + // add new padding + BBSizes[i] += 2; + delta += 2; + } + } + if (delta==0) + return; + } + MBBI = next(MBBI); + } + } } /// DecrementOldEntry - find the constant pool entry with index CPI @@ -729,44 +835,59 @@ static inline unsigned getUnconditionalBrDisp(int Opc) { return (Opc == ARM::tB) ? ((1<<10)-1)*2 : ((1<<23)-1)*4; } +/// AcceptWater - Small amount of common code factored out of the following. + +MachineBasicBlock* ARMConstantIslands::AcceptWater(MachineBasicBlock *WaterBB, + std::vector::iterator IP) { + DOUT << "found water in range\n"; + // Remove the original WaterList entry; we want subsequent + // insertions in this vicinity to go after the one we're + // about to insert. This considerably reduces the number + // of times we have to move the same CPE more than once. + WaterList.erase(IP); + // CPE goes before following block (NewMBB). + return next(MachineFunction::iterator(WaterBB)); +} + /// LookForWater - look for an existing entry in the WaterList in which /// we can place the CPE referenced from U so it's within range of U's MI. /// Returns true if found, false if not. If it returns true, *NewMBB -/// is set to the WaterList entry, and *PadNewWater is set to false if -/// the WaterList entry is an island. +/// is set to the WaterList entry. +/// For ARM, we prefer the water that's farthest away. For Thumb, prefer +/// water that will not introduce padding to water that will; within each +/// group, prefer the water that's farthest away. bool ARMConstantIslands::LookForWater(CPUser &U, unsigned UserOffset, - bool *PadNewWater, MachineBasicBlock** NewMBB) { + MachineBasicBlock** NewMBB) { + std::vector::iterator IPThatWouldPad; + MachineBasicBlock* WaterBBThatWouldPad = NULL; if (!WaterList.empty()) { for (std::vector::iterator IP = prior(WaterList.end()), B = WaterList.begin();; --IP) { MachineBasicBlock* WaterBB = *IP; if (WaterIsInRange(UserOffset, WaterBB, U.MaxDisp)) { - DOUT << "found water in range\n"; - // CPE goes before following block (NewMBB). - *NewMBB = next(MachineFunction::iterator(WaterBB)); - // If WaterBB is an island, don't pad the new island. - // If WaterBB is empty, go backwards until we find something that - // isn't. WaterBB may become empty if it's an island whose - // contents were moved farther back. - if (isThumb) { - MachineBasicBlock* BB = WaterBB; - while (BB->empty()) - BB = prior(MachineFunction::iterator(BB)); - if (BB->begin()->getOpcode() == ARM::CONSTPOOL_ENTRY) - *PadNewWater = false; + if (isThumb && + (BBOffsets[WaterBB->getNumber()] + + BBSizes[WaterBB->getNumber()])%4 != 0) { + // This is valid Water, but would introduce padding. Remember + // it in case we don't find any Water that doesn't do this. + if (!WaterBBThatWouldPad) { + WaterBBThatWouldPad = WaterBB; + IPThatWouldPad = IP; + } + } else { + *NewMBB = AcceptWater(WaterBB, IP); + return true; } - // Remove the original WaterList entry; we want subsequent - // insertions in this vicinity to go after the one we're - // about to insert. This considerably reduces the number - // of times we have to move the same CPE more than once. - WaterList.erase(IP); - return true; - } + } if (IP == B) break; } } + if (isThumb && WaterBBThatWouldPad) { + *NewMBB = AcceptWater(WaterBBThatWouldPad, IPThatWouldPad); + return true; + } return false; } @@ -786,16 +907,18 @@ void ARMConstantIslands::CreateNewWater(unsigned CPUserIndex, MachineBasicBlock *UserMBB = UserMI->getParent(); unsigned OffsetOfNextBlock = BBOffsets[UserMBB->getNumber()] + BBSizes[UserMBB->getNumber()]; - assert(OffsetOfNextBlock = BBOffsets[UserMBB->getNumber()+1]); + assert(OffsetOfNextBlock== BBOffsets[UserMBB->getNumber()+1]); // If the use is at the end of the block, or the end of the block - // is within range, make new water there. (The +2 or 4 below is - // for the unconditional branch we will be adding. If the block ends in - // an unconditional branch already, it is water, and is known to - // be out of range, so we'll always be adding one.) + // is within range, make new water there. (The addition below is + // for the unconditional branch we will be adding: 4 bytes on ARM, + // 2 on Thumb. Possible Thumb alignment padding is allowed for + // inside OffsetIsInRange. + // If the block ends in an unconditional branch already, it is water, + // and is known to be out of range, so we'll always be adding a branch.) if (&UserMBB->back() == UserMI || - OffsetIsInRange(UserOffset, OffsetOfNextBlock + (isThumb ? 2 : 4), - U.MaxDisp, !isThumb)) { + OffsetIsInRange(UserOffset, OffsetOfNextBlock + (isThumb ? 2: 4), + U.MaxDisp, !isThumb)) { DOUT << "Split at end of block\n"; if (&UserMBB->back() == UserMI) assert(BBHasFallthrough(UserMBB) && "Expected a fallthrough BB!"); @@ -821,11 +944,16 @@ void ARMConstantIslands::CreateNewWater(unsigned CPUserIndex, // not work well to put CPE as far forward as possible, since then // CPE' cannot immediately follow it (that location is 2 bytes // farther away from I+1 than CPE was from I) and we'd need to create - // a new island. + // a new island. So, we make a first guess, then walk through the + // instructions between the one currently being looked at and the + // possible insertion point, and make sure any other instructions + // that reference CPEs will be able to use the same island area; + // if not, we back up the insertion point. + // The 4 in the following is for the unconditional branch we'll be - // inserting (allows for long branch on Thumb). The 2 or 0 is for - // alignment of the island. - unsigned BaseInsertOffset = UserOffset + U.MaxDisp -4 + (isThumb ? 2 : 0); + // inserting (allows for long branch on Thumb). Alignment of the + // island is handled inside OffsetIsInRange. + unsigned BaseInsertOffset = UserOffset + U.MaxDisp -4; // This could point off the end of the block if we've already got // constant pool entries following this block; only the last one is // in the water list. Back past any possible branches (allow for a @@ -871,7 +999,8 @@ bool ARMConstantIslands::HandleConstantPoolUser(MachineFunction &Fn, unsigned CPI = CPEMI->getOperand(1).getConstantPoolIndex(); unsigned Size = CPEMI->getOperand(2).getImm(); MachineBasicBlock *NewMBB; - // Compute this only once, it's expensive + // Compute this only once, it's expensive. The 4 or 8 is the value the + // hardware keeps in the PC (2 insns ahead of the reference). unsigned UserOffset = GetOffsetOf(UserMI) + (isThumb ? 4 : 8); // Special case: tLEApcrel are two instructions MI's. The actual user is the @@ -892,9 +1021,8 @@ bool ARMConstantIslands::HandleConstantPoolUser(MachineFunction &Fn, // Look for water where we can place this CPE. We look for the farthest one // away that will work. Forward references only for now (although later // we might find some that are backwards). - bool PadNewWater = true; - if (!LookForWater(U, UserOffset, &PadNewWater, &NewMBB)) { + if (!LookForWater(U, UserOffset, &NewMBB)) { // No water found. DOUT << "No water found\n"; CreateNewWater(CPUserIndex, UserOffset, &NewMBB); @@ -917,11 +1045,12 @@ bool ARMConstantIslands::HandleConstantPoolUser(MachineFunction &Fn, CPEntries[CPI].push_back(CPEntry(U.CPEMI, ID, 1)); NumCPEs++; + BBOffsets[NewIsland->getNumber()] = BBOffsets[NewMBB->getNumber()]; // Compensate for .align 2 in thumb mode. - if (isThumb && PadNewWater) Size += 2; + if (isThumb && BBOffsets[NewIsland->getNumber()]%4 != 0) + Size += 2; // Increase the size of the island block to account for the new entry. BBSizes[NewIsland->getNumber()] += Size; - BBOffsets[NewIsland->getNumber()] = BBOffsets[NewMBB->getNumber()]; AdjustBBOffsetsAfter(NewIsland, Size); // Finally, change the CPI in the instruction operand to be ID. @@ -940,28 +1069,26 @@ bool ARMConstantIslands::HandleConstantPoolUser(MachineFunction &Fn, /// sizes and offsets of impacted basic blocks. void ARMConstantIslands::RemoveDeadCPEMI(MachineInstr *CPEMI) { MachineBasicBlock *CPEBB = CPEMI->getParent(); + unsigned Size = CPEMI->getOperand(2).getImm(); + CPEMI->eraseFromParent(); + BBSizes[CPEBB->getNumber()] -= Size; + // All succeeding offsets have the current size value added in, fix this. if (CPEBB->empty()) { - // In thumb mode, the size of island is padded by two to compensate for - // the alignment requirement. Thus it will now be 2 when the block is + // In thumb mode, the size of island may be padded by two to compensate for + // the alignment requirement. Then it will now be 2 when the block is // empty, so fix this. // All succeeding offsets have the current size value added in, fix this. if (BBSizes[CPEBB->getNumber()] != 0) { - AdjustBBOffsetsAfter(CPEBB, -BBSizes[CPEBB->getNumber()]); + Size += BBSizes[CPEBB->getNumber()]; BBSizes[CPEBB->getNumber()] = 0; } - // An island has only one predecessor BB and one successor BB. Check if - // this BB's predecessor jumps directly to this BB's successor. This - // shouldn't happen currently. - assert(!BBIsJumpedOver(CPEBB) && "How did this happen?"); - // FIXME: remove the empty blocks after all the work is done? - } else { - unsigned Size = CPEMI->getOperand(2).getImm(); - BBSizes[CPEBB->getNumber()] -= Size; - // All succeeding offsets have the current size value added in, fix this. - AdjustBBOffsetsAfter(CPEBB, -Size); } - - CPEMI->eraseFromParent(); + AdjustBBOffsetsAfter(CPEBB, -Size); + // An island has only one predecessor BB and one successor BB. Check if + // this BB's predecessor jumps directly to this BB's successor. This + // shouldn't happen currently. + assert(!BBIsJumpedOver(CPEBB) && "How did this happen?"); + // FIXME: remove the empty blocks after all the work is done? } /// RemoveUnusedCPEntries - Remove constant pool entries whose refcounts @@ -992,9 +1119,18 @@ bool ARMConstantIslands::BBIsInRange(MachineInstr *MI,MachineBasicBlock *DestBB, DOUT << "Branch of destination BB#" << DestBB->getNumber() << " from BB#" << MI->getParent()->getNumber() << " max delta=" << MaxDisp - << " at offset " << int(DestOffset-BrOffset) << "\t" << *MI; + << " from " << GetOffsetOf(MI) << " to " << DestOffset + << " offset " << int(DestOffset-BrOffset) << "\t" << *MI; - return OffsetIsInRange(BrOffset, DestOffset, MaxDisp, true); + if (BrOffset <= DestOffset) { + // Branch before the Dest. + if (DestOffset-BrOffset <= MaxDisp) + return true; + } else { + if (BrOffset-DestOffset <= MaxDisp) + return true; + } + return false; } /// FixUpImmediateBr - Fix up an immediate branch whose destination is too far @@ -1088,8 +1224,10 @@ ARMConstantIslands::FixUpConditionalBr(MachineFunction &Fn, ImmBranch &Br) { // branch to the destination. int delta = ARM::GetInstSize(&MBB->back()); BBSizes[MBB->getNumber()] -= delta; - AdjustBBOffsetsAfter(MBB, -delta); + MachineBasicBlock* SplitBB = next(MachineFunction::iterator(MBB)); + AdjustBBOffsetsAfter(SplitBB, -delta); MBB->back().eraseFromParent(); + // BBOffsets[SplitBB] is wrong temporarily, fixed below } MachineBasicBlock *NextBB = next(MachineFunction::iterator(MBB)); diff --git a/lib/Target/ARM/ARMInstrInfo.cpp b/lib/Target/ARM/ARMInstrInfo.cpp index a5ab09c993d..de3a7fda4d3 100644 --- a/lib/Target/ARM/ARMInstrInfo.cpp +++ b/lib/Target/ARM/ARMInstrInfo.cpp @@ -469,12 +469,13 @@ unsigned ARM::GetInstSize(MachineInstr *MI) { assert(JTI < JT.size()); // Thumb instructions are 2 byte aligned, but JT entries are 4 byte // 4 aligned. The assembler / linker may add 2 byte padding just before - // the JT entries. Use + 4 even for tBR_JTr to purposely over-estimate - // the size the jumptable. + // the JT entries. The size does not include this padding; the + // constant islands pass does separate bookkeeping for it. // FIXME: If we know the size of the function is less than (1 << 16) *2 // bytes, we can use 16-bit entries instead. Then there won't be an // alignment issue. - return getNumJTEntries(JT, JTI) * 4 + 4; + return getNumJTEntries(JT, JTI) * 4 + + (MI->getOpcode()==ARM::tBR_JTr ? 2 : 4); } default: // Otherwise, pseudo-instruction sizes are zero.