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Rewrite of Thumb constant islands handling (exact allowance for padding

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around islands and jump tables).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36573 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dale Johannesen 2007-04-29 19:19:30 +00:00
parent 8650199fbb
commit 8593e41855
2 changed files with 226 additions and 87 deletions
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306
lib/Target/ARM/ARMConstantIslandPass.cpp
View File

@ -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<unsigned> 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<unsigned> 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<MachineBasicBlock*>::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<ARMFunctionInfo>();
TII = Fn.getTarget().getInstrInfo();
AFI = Fn.getInfo<ARMFunctionInfo>();
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; i<BB->getParent()->getNumBlockIDs(); i++)
void ARMConstantIslands::AdjustBBOffsetsAfter(MachineBasicBlock *BB,
int delta) {
MachineFunction::iterator MBBI = BB; MBBI = next(MBBI);
for(unsigned i=BB->getNumber()+1; i<BB->getParent()->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<MachineBasicBlock*>::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<MachineBasicBlock*>::iterator IPThatWouldPad;
MachineBasicBlock* WaterBBThatWouldPad = NULL;
if (!WaterList.empty()) {
for (std::vector<MachineBasicBlock*>::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));

7
lib/Target/ARM/ARMInstrInfo.cpp
View File

@ -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.