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Removed WaterListOffset, inserted BBOffsets. Remove TODO item about this 

from README.
When no water available, use end of block if in range.  (More to do here.)

llvm-svn: 34563
This commit is contained in:
Dale Johannesen 2007-02-25 00:47:03 +00:00
parent 468ad911cb
commit 01ee5750f4
2 changed files with 113 additions and 108 deletions
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205
llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
View File

@ -4,6 +4,7 @@
//
// This file was developed by Chris Lattner and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
// Substantial modifications by Evan Cheng and Dale Johannesen.
//
//===----------------------------------------------------------------------===//
//
@ -49,21 +50,19 @@ namespace {
class VISIBILITY_HIDDEN ARMConstantIslands : public MachineFunctionPass {
/// NextUID - Assign unique ID's to CPE's.
unsigned NextUID;
/// BBSizes - The size of each MachineBasicBlock in bytes of code, indexed
/// by MBB Number.
std::vector<unsigned> BBSizes;
/// BBOffsets - the offset of each MBB in bytes, starting from 0.
std::vector<unsigned> BBOffsets;
/// WaterList - A sorted list of basic blocks where islands could be placed
/// (i.e. blocks that don't fall through to the following block, due
/// to a return, unreachable, or unconditional branch).
std::vector<MachineBasicBlock*> WaterList;
// WaterListOffsets - the offset of the beginning of each WaterList block.
// This is computed as needed in HandleConstantPoolUser; not necessarily
// valid at arbitrary times.
std::vector<unsigned> WaterListOffsets;
/// CPUser - One user of a constant pool, keeping the machine instruction
/// pointer, the constant pool being referenced, and the max displacement
/// allowed from the instruction to the CP.
@ -139,16 +138,17 @@ namespace {
const std::vector<MachineInstr*> &CPEMIs);
MachineBasicBlock *SplitBlockBeforeInstr(MachineInstr *MI);
void UpdateForInsertedWaterBlock(MachineBasicBlock *NewBB);
void AdjustBBOffsetsAfter(MachineBasicBlock *BB, int delta);
bool DecrementOldEntry(unsigned CPI, MachineInstr* CPEMI, unsigned Size);
void ComputeWaterListOffsets(MachineFunction &Fn);
int LookForExistingCPEntry(CPUser& U, unsigned UserOffset);
bool HandleConstantPoolUser(MachineFunction &Fn, CPUser &U);
bool CPEIsInRange(MachineInstr *MI, unsigned UserOffset,
MachineInstr *CPEMI, unsigned Disp,
bool DoDump);
bool WaterIsInRange(unsigned UserOffset,
std::vector<MachineBasicBlock*>::iterator IP,
bool WaterIsInRange(unsigned UserOffset, MachineBasicBlock *Water,
unsigned Disp);
bool OffsetIsInRange(unsigned UserOffset, unsigned TrialOffset,
unsigned Disp, bool NegativeOK);
bool BBIsInRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned Disp);
bool FixUpImmediateBr(MachineFunction &Fn, ImmBranch &Br);
bool FixUpConditionalBr(MachineFunction &Fn, ImmBranch &Br);
@ -156,7 +156,6 @@ namespace {
bool UndoLRSpillRestore();
unsigned GetOffsetOf(MachineInstr *MI) const;
unsigned GetOffsetOf(MachineBasicBlock *MBB) const;
};
}
@ -213,6 +212,7 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &Fn) {
MadeChange |= UndoLRSpillRestore();
BBSizes.clear();
BBOffsets.clear();
WaterList.clear();
CPUsers.clear();
CPEntries.clear();
@ -293,6 +293,7 @@ ARMConstantIslands::CPEntry
/// and finding all of the constant pool users.
void ARMConstantIslands::InitialFunctionScan(MachineFunction &Fn,
const std::vector<MachineInstr*> &CPEMIs) {
unsigned Offset = 0;
for (MachineFunction::iterator MBBI = Fn.begin(), E = Fn.end();
MBBI != E; ++MBBI) {
MachineBasicBlock &MBB = *MBBI;
@ -419,6 +420,8 @@ void ARMConstantIslands::InitialFunctionScan(MachineFunction &Fn,
MBBSize += 2;
BBSizes.push_back(MBBSize);
BBOffsets.push_back(Offset);
Offset += MBBSize;
}
}
@ -431,11 +434,7 @@ unsigned ARMConstantIslands::GetOffsetOf(MachineInstr *MI) const {
// The offset is composed of two things: the sum of the sizes of all MBB's
// before this instruction's block, and the offset from the start of the block
// it is in.
unsigned Offset = 0;
// Sum block sizes before MBB.
for (unsigned BB = 0, e = MBB->getNumber(); BB != e; ++BB)
Offset += BBSizes[BB];
unsigned Offset = BBOffsets[MBB->getNumber()];
// Sum instructions before MI in MBB.
for (MachineBasicBlock::iterator I = MBB->begin(); ; ++I) {
@ -445,18 +444,6 @@ unsigned ARMConstantIslands::GetOffsetOf(MachineInstr *MI) const {
}
}
/// GetOffsetOf - Return the current offset of the specified machine BB
/// from the start of the function. This offset changes as stuff is moved
/// around inside the function.
unsigned ARMConstantIslands::GetOffsetOf(MachineBasicBlock *MBB) const {
// Sum block sizes before MBB.
unsigned Offset = 0;
for (unsigned BB = 0, e = MBB->getNumber(); BB != e; ++BB)
Offset += BBSizes[BB];
return Offset;
}
/// CompareMBBNumbers - Little predicate function to sort the WaterList by MBB
/// ID.
static bool CompareMBBNumbers(const MachineBasicBlock *LHS,
@ -474,6 +461,9 @@ void ARMConstantIslands::UpdateForInsertedWaterBlock(MachineBasicBlock *NewBB) {
// Insert a size into BBSizes to align it properly with the (newly
// renumbered) block numbers.
BBSizes.insert(BBSizes.begin()+NewBB->getNumber(), 0);
// Likewise for BBOffsets.
BBOffsets.insert(BBOffsets.begin()+NewBB->getNumber(), 0);
// Next, update WaterList. Specifically, we need to add NewMBB as having
// available water after it.
@ -528,6 +518,9 @@ MachineBasicBlock *ARMConstantIslands::SplitBlockBeforeInstr(MachineInstr *MI) {
// renumbered) block numbers.
BBSizes.insert(BBSizes.begin()+NewBB->getNumber(), 0);
// Likewise for BBOffsets.
BBOffsets.insert(BBOffsets.begin()+NewBB->getNumber(), 0);
// Next, update WaterList. Specifically, we need to add OrigMBB as having
// available water after it (but not if it's already there, which happens
// when splitting before a conditional branch that is followed by an
@ -547,44 +540,57 @@ MachineBasicBlock *ARMConstantIslands::SplitBlockBeforeInstr(MachineInstr *MI) {
I != E; ++I)
NewBBSize += ARM::GetInstSize(I);
unsigned OrigBBI = OrigBB->getNumber();
unsigned NewBBI = NewBB->getNumber();
// Set the size of NewBB in BBSizes.
BBSizes[NewBB->getNumber()] = NewBBSize;
BBSizes[NewBBI] = NewBBSize;
// We removed instructions from UserMBB, subtract that off from its size.
// Add 2 or 4 to the block to count the unconditional branch we added to it.
BBSizes[OrigBB->getNumber()] -= NewBBSize - (isThumb ? 2 : 4);
unsigned delta = isThumb ? 2 : 4;
BBSizes[OrigBBI] -= NewBBSize - delta;
// ...and adjust BBOffsets for NewBB accordingly.
BBOffsets[NewBBI] = BBOffsets[OrigBBI] + BBSizes[OrigBBI];
// All BBOffsets following these blocks must be modified.
AdjustBBOffsetsAfter(NewBB, delta);
return NewBB;
}
//// OffsetIsInRange - Checks whether UserOffset is within MaxDisp of
/// TrialOffset.
bool ARMConstantIslands::OffsetIsInRange(unsigned UserOffset,
unsigned TrialOffset, unsigned MaxDisp, bool NegativeOK) {
if (UserOffset <= TrialOffset) {
// User before the Trial.
if (TrialOffset-UserOffset <= MaxDisp)
return true;
} else if (NegativeOK) {
if (UserOffset-TrialOffset <= MaxDisp)
return true;
}
return false;
}
/// WaterIsInRange - Returns true if a CPE placed after the specified
/// Water (a basic block) will be in range for the specific MI.
bool ARMConstantIslands::WaterIsInRange(unsigned UserOffset,
std::vector<MachineBasicBlock*>::iterator IP,
unsigned MaxDisp)
MachineBasicBlock* Water, unsigned MaxDisp)
{
MachineBasicBlock *Water = *IP;
unsigned Index = IP - WaterList.begin();
unsigned CPEOffset = WaterListOffsets[Index] +
bool isThumb = AFI->isThumbFunction();
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 (AFI->isThumbFunction() &&
if (isThumb &&
(Water->empty() ||
Water->begin()->getOpcode() != ARM::CONSTPOOL_ENTRY))
CPEOffset += 2;
if (UserOffset <= CPEOffset) {
// User before the CPE.
if (CPEOffset-UserOffset <= MaxDisp)
return true;
} else if (!AFI->isThumbFunction()) {
// Thumb LDR cannot encode negative offset.
if (UserOffset-CPEOffset <= MaxDisp)
return true;
}
return false;
return OffsetIsInRange (UserOffset, CPEOffset, MaxDisp, !isThumb);
}
/// CPEIsInRange - Returns true if the distance between specific MI and
@ -594,7 +600,8 @@ bool ARMConstantIslands::CPEIsInRange(MachineInstr *MI, unsigned UserOffset,
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 = AFI->isThumbFunction() ? 2 : 0;
bool isThumb = AFI->isThumbFunction();
unsigned AlignAdj = isThumb ? 2 : 0;
unsigned CPEOffset = GetOffsetOf(CPEMI) + AlignAdj;
if (DoDump) {
@ -605,16 +612,7 @@ bool ARMConstantIslands::CPEIsInRange(MachineInstr *MI, unsigned UserOffset,
<< " offset=" << int(CPEOffset-UserOffset) << "\t" << *MI;
}
if (UserOffset <= CPEOffset) {
// User before the CPE.
if (CPEOffset-UserOffset <= MaxDisp)
return true;
} else if (!AFI->isThumbFunction()) {
// Thumb LDR cannot encode negative offset.
if (UserOffset-CPEOffset <= MaxDisp)
return true;
}
return false;
return OffsetIsInRange(UserOffset, CPEOffset, MaxDisp, !isThumb);
}
/// BBIsJumpedOver - Return true of the specified basic block's only predecessor
@ -631,6 +629,13 @@ static bool BBIsJumpedOver(MachineBasicBlock *MBB) {
return false;
}
void ARMConstantIslands::AdjustBBOffsetsAfter(MachineBasicBlock *BB, int delta)
{
MachineFunction::iterator MBBI = BB->getParent()->end();
for(int i=BB->getNumber()+1; i<=prior(MBBI)->getNumber(); i++)
BBOffsets[i] += delta;
}
/// DecrementOldEntry - find the constant pool entry with index CPI
/// and instruction CPEMI, and decrement its refcount. If the refcount
/// becomes 0 remove the entry and instruction. Returns true if we removed
@ -647,14 +652,21 @@ bool ARMConstantIslands::DecrementOldEntry(unsigned CPI, MachineInstr *CPEMI,
// 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
// empty, so fix this.
BBSizes[OldCPEBB->getNumber()] = 0;
// All succeeding offsets have the current size value added in, fix this.
if (BBSizes[OldCPEBB->getNumber()] != 0) {
AdjustBBOffsetsAfter(OldCPEBB, -BBSizes[OldCPEBB->getNumber()]);
BBSizes[OldCPEBB->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(OldCPEBB) && "How did this happen?");
// FIXME: remove the empty blocks after all the work is done?
} else
} else {
BBSizes[OldCPEBB->getNumber()] -= Size;
// All succeeding offsets have the current size value added in, fix this.
AdjustBBOffsetsAfter(OldCPEBB, -Size);
}
OldCPE->CPEMI->eraseFromParent();
OldCPE->CPEMI = NULL;
NumCPEs--;
@ -663,25 +675,6 @@ bool ARMConstantIslands::DecrementOldEntry(unsigned CPI, MachineInstr *CPEMI,
return false;
}
/// ComputeWaterListOffsets - just what you think.
/// This vector is built to avoid re-adding BBSizes for each WaterBB under test
/// (which would cause the algorithm to be n^2).
void ARMConstantIslands::ComputeWaterListOffsets(MachineFunction &Fn) {
unsigned WaterListIndex = 0;
unsigned Offset = 0;
unsigned BB = 0;
WaterListOffsets.clear();
for (MachineFunction::iterator MBBI = Fn.begin(), E = Fn.end();
MBBI != E; ++BB, ++MBBI) {
MachineBasicBlock *MBB = MBBI;
if (MBB == WaterList[WaterListIndex]) {
WaterListOffsets.push_back(Offset);
WaterListIndex++;
}
Offset += BBSizes[BB];
}
}
/// LookForCPEntryInRange - see if the currently referenced CPE is in range;
/// if not, see if an in-range clone of the CPE is in range, and if so,
/// change the data structures so the user references the clone. Returns:
@ -759,15 +752,10 @@ bool ARMConstantIslands::HandleConstantPoolUser(MachineFunction &Fn, CPUser &U){
// we might find some that are backwards).
bool WaterFound = false;
if (!WaterList.empty()) {
// Compute offsets for the blocks in the current WaterList.
// It is a big compile-time speed win to do this only once
// rather than for each WaterList entry.
ComputeWaterListOffsets(Fn);
assert(WaterList.size() == WaterListOffsets.size());
for (std::vector<MachineBasicBlock*>::iterator IP = prior(WaterList.end()),
B = WaterList.begin();; --IP) {
MachineBasicBlock* WaterBB = *IP;
if (WaterIsInRange(UserOffset, IP, U.MaxDisp)) {
if (WaterIsInRange(UserOffset, WaterBB, U.MaxDisp)) {
WaterFound = true;
DOUT << "found water in range\n";
// CPE goes before following block (NewMBB).
@ -786,23 +774,40 @@ bool ARMConstantIslands::HandleConstantPoolUser(MachineFunction &Fn, CPUser &U){
if (!WaterFound) {
// No water found.
// Solution of last resort: split the user's MBB right after the user
// and insert a clone of the CPE into the newly created water.
DOUT << "No water found\n";
MachineBasicBlock *UserMBB = UserMI->getParent();
unsigned TrialOffset = BBOffsets[UserMBB->getNumber()] +
BBSizes[UserMBB->getNumber()] +
isThumb ? 2 : 4; /* for branch to be added */
// TODO: Search for the best place to split the code. In practice, using
// loop nesting information to insert these guys outside of loops would be
// sufficient.
if (&UserMBB->back() == UserMI) {
assert(BBHasFallthrough(UserMBB) && "Expected a fallthrough BB!");
// If the use is at the end of the block, or the end of the block
// is within range, make new water there. (If the block ends in
// an unconditional branch already, it is water, and is known to
// be out of range; so it's OK to assume above we'll be adding a Br.)
if (&UserMBB->back() == UserMI ||
OffsetIsInRange(UserOffset, TrialOffset, U.MaxDisp, !isThumb)) {
if (&UserMBB->back() == UserMI)
assert(BBHasFallthrough(UserMBB) && "Expected a fallthrough BB!");
NewMBB = next(MachineFunction::iterator(UserMBB));
// Add an unconditional branch from UserMBB to fallthrough block.
// Note the new unconditional branch is not being recorded.
BuildMI(UserMBB, TII->get(isThumb ? ARM::tB : ARM::B)).addMBB(NewMBB);
BBSizes[UserMBB->getNumber()] += isThumb ? 2 : 4;
int delta = isThumb ? 2 : 4;
BBSizes[UserMBB->getNumber()] += delta;
AdjustBBOffsetsAfter(UserMBB, delta);
} else {
// What a big block. Find a place within the block to split it.
// This is a little tricky on Thumb since instructions are 2 bytes
// and constant pool entries are 4 bytes: if instruction I references
// island CPE, and instruction I+1 references CPE', it will
// 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.
// Solution of last resort: split the user's MBB right after the user
// and insert a clone of the CPE into the newly created water.
MachineInstr *NextMI = next(MachineBasicBlock::iterator(UserMI));
NewMBB = SplitBlockBeforeInstr(NextMI);
}
@ -829,6 +834,8 @@ bool ARMConstantIslands::HandleConstantPoolUser(MachineFunction &Fn, CPUser &U){
if (isThumb) 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.
for (unsigned i = 0, e = UserMI->getNumOperands(); i != e; ++i)
@ -848,21 +855,14 @@ bool ARMConstantIslands::BBIsInRange(MachineInstr *MI,MachineBasicBlock *DestBB,
unsigned MaxDisp) {
unsigned PCAdj = AFI->isThumbFunction() ? 4 : 8;
unsigned BrOffset = GetOffsetOf(MI) + PCAdj;
unsigned DestOffset = GetOffsetOf(DestBB);
unsigned DestOffset = BBOffsets[DestBB->getNumber()];
DOUT << "Branch of destination BB#" << DestBB->getNumber()
<< " from BB#" << MI->getParent()->getNumber()
<< " max delta=" << MaxDisp
<< " at offset " << int(DestOffset-BrOffset) << "\t" << *MI;
if (BrOffset <= DestOffset) {
if (DestOffset - BrOffset <= MaxDisp)
return true;
} else {
if (BrOffset - DestOffset <= MaxDisp)
return true;
}
return false;
return OffsetIsInRange(BrOffset, DestOffset, MaxDisp, true);
}
/// FixUpImmediateBr - Fix up an immediate branch whose destination is too far
@ -894,6 +894,7 @@ ARMConstantIslands::FixUpUnconditionalBr(MachineFunction &Fn, ImmBranch &Br) {
Br.MaxDisp = (1 << 21) * 2;
MI->setInstrDescriptor(TII->get(ARM::tBfar));
BBSizes[MBB->getNumber()] += 2;
AdjustBBOffsetsAfter(MBB, 2);
HasFarJump = true;
NumUBrFixed++;
@ -977,7 +978,9 @@ ARMConstantIslands::FixUpConditionalBr(MachineFunction &Fn, ImmBranch &Br) {
MI->eraseFromParent();
// Increase the size of MBB to account for the new unconditional branch.
BBSizes[MBB->getNumber()] += ARM::GetInstSize(&MBB->back());
int delta = ARM::GetInstSize(&MBB->back());
BBSizes[MBB->getNumber()] += delta;
AdjustBBOffsetsAfter(MBB, delta);
return true;
}

16
llvm/lib/Target/ARM/README.txt
View File

@ -21,17 +21,19 @@ The constant island pass has been much improved; all the todo items in the
previous version of this document have been addressed. However, there are still
things that can be done:
1. When there isn't an existing water, the current MBB is split right after the
use. It would be profitable to look farther forward, especially on Thumb,
1. When there isn't an existing water, the current MBB is split right after
the use. It would be profitable to look farther forward, especially on Thumb,
where negative offsets won't work.
Now it will put the island at the end of the block if that is in range. If it
is not in range things still work as above, which is poor on Thumb.
2. WaterBlockListOffsets might be maintained throughout, rather than computed
when it is needed. This would probably lead to faster compile times.
Similarly, the offsets of blocks might be maintained throughout.
3. There may be some advantage to trying to be smarter about the initial
2. There may be some advantage to trying to be smarter about the initial
placement, rather than putting everything at the end.
3. The handling of 2-byte padding for Thumb is overly conservative. There
would be a small gain to keeping accurate track of the padding (which would
require aligning functions containing constant pools to 4-byte boundaries).
//===---------------------------------------------------------------------===//
We need to start generating predicated instructions. The .td files have a way