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Update TB[BH] layout optimization. Add support for moving the target block 

to directly follow the jump table. Move the layout changes to prior to any
constant island handling.

llvm-svn: 86999
This commit is contained in:
Jim Grosbach 2009-11-12 17:25:07 +00:00
parent bc55fe26c6
commit 5d57714e6c
1 changed files with 115 additions and 33 deletions
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148
llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
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@ -44,6 +44,7 @@ STATISTIC(NumT2CPShrunk, "Number of Thumb2 constantpool instructions shrunk");
STATISTIC(NumT2BrShrunk, "Number of Thumb2 immediate branches shrunk");
STATISTIC(NumCBZ, "Number of CBZ / CBNZ formed");
STATISTIC(NumJTMoved, "Number of jump table destination blocks moved");
STATISTIC(NumJTInserted, "Number of jump table intermediate blocks inserted");
static cl::opt<bool>
@ -181,6 +182,7 @@ namespace {
void DoInitialPlacement(MachineFunction &MF,
std::vector<MachineInstr*> &CPEMIs);
CPEntry *findConstPoolEntry(unsigned CPI, const MachineInstr *CPEMI);
void JumpTableFunctionScan(MachineFunction &MF);
void InitialFunctionScan(MachineFunction &MF,
const std::vector<MachineInstr*> &CPEMIs);
MachineBasicBlock *SplitBlockBeforeInstr(MachineInstr *MI);
@ -208,6 +210,7 @@ namespace {
bool UndoLRSpillRestore();
bool OptimizeThumb2Instructions(MachineFunction &MF);
bool OptimizeThumb2Branches(MachineFunction &MF);
bool ReorderThumb2JumpTables(MachineFunction &MF);
bool OptimizeThumb2JumpTables(MachineFunction &MF);
MachineBasicBlock *AdjustJTTargetBlockForward(MachineBasicBlock *BB,
MachineBasicBlock *JTBB);
@ -271,6 +274,20 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &MF) {
// the numbers agree with the position of the block in the function.
MF.RenumberBlocks();
// Try to reorder and otherwise adjust the block layout to make good use
// of the TB[BH] instructions.
bool MadeChange = false;
if (isThumb2 && AdjustJumpTableBlocks) {
JumpTableFunctionScan(MF);
MadeChange |= ReorderThumb2JumpTables(MF);
// Data is out of date, so clear it. It'll be re-computed later.
BBSizes.clear();
BBOffsets.clear();
T2JumpTables.clear();
// Blocks may have shifted around. Keep the numbering up to date.
MF.RenumberBlocks();
}
// Thumb1 functions containing constant pools get 4-byte alignment.
// This is so we can keep exact track of where the alignment padding goes.
@ -301,7 +318,6 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &MF) {
// Iteratively place constant pool entries and fix up branches until there
// is no change.
bool MadeChange = false;
unsigned NoCPIters = 0, NoBRIters = 0;
while (true) {
bool CPChange = false;
@ -418,6 +434,39 @@ ARMConstantIslands::CPEntry
return NULL;
}
/// JumpTableFunctionScan - Do a scan of the function, building up
/// information about the sizes of each block and the locations of all
/// the jump tables.
void ARMConstantIslands::JumpTableFunctionScan(MachineFunction &MF) {
unsigned Offset = 0;
for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
MBBI != E; ++MBBI) {
MachineBasicBlock &MBB = *MBBI;
unsigned MBBSize = 0;
for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
I != E; ++I) {
// Add instruction size to MBBSize.
MBBSize += TII->GetInstSizeInBytes(I);
int Opc = I->getOpcode();
if (I->getDesc().isBranch()) {
switch (Opc) {
default:
continue; // Ignore other JT branches
case ARM::t2BR_JT:
T2JumpTables.push_back(I);
continue; // Does not get an entry in ImmBranches
}
}
}
BBSizes.push_back(MBBSize);
BBOffsets.push_back(Offset);
Offset += MBBSize;
}
}
/// InitialFunctionScan - Do the initial scan of the function, building up
/// information about the sizes of each block, the location of all the water,
/// and finding all of the constant pool users.
@ -1561,7 +1610,6 @@ bool ARMConstantIslands::OptimizeThumb2Branches(MachineFunction &MF) {
return MadeChange;
}
/// OptimizeThumb2JumpTables - Use tbb / tbh instructions to generate smaller
/// jumptables when it's possible.
bool ARMConstantIslands::OptimizeThumb2JumpTables(MachineFunction &MF) {
@ -1580,33 +1628,10 @@ bool ARMConstantIslands::OptimizeThumb2JumpTables(MachineFunction &MF) {
unsigned JTI = JTOP.getIndex();
assert(JTI < JT.size());
// We prefer if target blocks for the jump table come after the jump
// instruction so we can use TB[BH]. Loop through the target blocks
// and try to adjust them such that that's true.
unsigned JTOffset = GetOffsetOf(MI) + 4;
const std::vector<MachineBasicBlock*> &JTBBs = JT[JTI].MBBs;
if (AdjustJumpTableBlocks) {
for (unsigned j = 0, ee = JTBBs.size(); j != ee; ++j) {
MachineBasicBlock *MBB = JTBBs[j];
unsigned DstOffset = BBOffsets[MBB->getNumber()];
if (DstOffset < JTOffset) {
// The destination precedes the switch. Try to move the block forward
// so we have a positive offset.
MachineBasicBlock *NewBB =
AdjustJTTargetBlockForward(MBB, MI->getParent());
if (NewBB) {
MJTI->ReplaceMBBInJumpTables(JTBBs[j], NewBB);
JTOffset = GetOffsetOf(MI) + 4;
DstOffset = BBOffsets[MBB->getNumber()];
}
}
}
}
bool ByteOk = true;
bool HalfWordOk = true;
JTOffset = GetOffsetOf(MI) + 4;
unsigned JTOffset = GetOffsetOf(MI) + 4;
const std::vector<MachineBasicBlock*> &JTBBs = JT[JTI].MBBs;
for (unsigned j = 0, ee = JTBBs.size(); j != ee; ++j) {
MachineBasicBlock *MBB = JTBBs[j];
unsigned DstOffset = BBOffsets[MBB->getNumber()];
@ -1693,16 +1718,73 @@ bool ARMConstantIslands::OptimizeThumb2JumpTables(MachineFunction &MF) {
return MadeChange;
}
/// ReorderThumb2JumpTables - Use tbb / tbh instructions to generate smaller
/// jumptables when it's possible.
bool ARMConstantIslands::ReorderThumb2JumpTables(MachineFunction &MF) {
bool MadeChange = false;
MachineJumpTableInfo *MJTI = MF.getJumpTableInfo();
const std::vector<MachineJumpTableEntry> &JT = MJTI->getJumpTables();
for (unsigned i = 0, e = T2JumpTables.size(); i != e; ++i) {
MachineInstr *MI = T2JumpTables[i];
const TargetInstrDesc &TID = MI->getDesc();
unsigned NumOps = TID.getNumOperands();
unsigned JTOpIdx = NumOps - (TID.isPredicable() ? 3 : 2);
MachineOperand JTOP = MI->getOperand(JTOpIdx);
unsigned JTI = JTOP.getIndex();
assert(JTI < JT.size());
// We prefer if target blocks for the jump table come after the jump
// instruction so we can use TB[BH]. Loop through the target blocks
// and try to adjust them such that that's true.
unsigned JTOffset = GetOffsetOf(MI) + 4;
const std::vector<MachineBasicBlock*> &JTBBs = JT[JTI].MBBs;
for (unsigned j = 0, ee = JTBBs.size(); j != ee; ++j) {
MachineBasicBlock *MBB = JTBBs[j];
unsigned DstOffset = BBOffsets[MBB->getNumber()];
if (DstOffset < JTOffset) {
// The destination precedes the switch. Try to move the block forward
// so we have a positive offset.
MachineBasicBlock *NewBB =
AdjustJTTargetBlockForward(MBB, MI->getParent());
if (NewBB)
MJTI->ReplaceMBBInJumpTables(JTBBs[j], NewBB);
MadeChange = true;
}
}
}
return MadeChange;
}
MachineBasicBlock *ARMConstantIslands::
AdjustJTTargetBlockForward(MachineBasicBlock *BB, MachineBasicBlock *JTBB)
{
MachineFunction &MF = *BB->getParent();
// FIXME: For now, instead of moving the block, we'll create a new block
// immediate following the jump that's an unconditional branch to the
// actual target. This is obviously not what we want for a real solution,
// but it's useful for proof of concept, and it may be a useful fallback
// later for cases where we otherwise can't move a block.
// FIXME: If it's a small block terminated by an unconditional branch,
// try to move it; otherwise, create a new block following the jump
// table that branches back to the actual target. This is an overly
// simplistic heuristic here for proof-of-concept.
int BBI = BB->getNumber();
int Size = BBSizes[BBI];
MachineBasicBlock *TBB = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
// If the block terminator isn't analyzable, don't try to move the block
if (TII->AnalyzeBranch(*BB, TBB, FBB, Cond))
return NULL;
// If the block is small and ends in an unconditional branch, move it.
if (Size < 50 && Cond.empty()) {
MachineFunction::iterator OldPrior = prior(BB);
BB->moveAfter(JTBB);
OldPrior->updateTerminator();
//BB->updateTerminator();
++NumJTMoved;
return NULL;
}
// Create a new MBB for the code after the jump BB.
MachineBasicBlock *NewBB =
@ -1750,6 +1832,6 @@ AdjustJTTargetBlockForward(MachineBasicBlock *BB, MachineBasicBlock *JTBB)
// All BBOffsets following these blocks must be modified.
AdjustBBOffsetsAfter(NewBB, 4);
++NumJTMoved;
++NumJTInserted;
return NewBB;
}