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- In thumb mode, if size of MachineFunction is >= 2048, force LR to be

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spilled (if it is not already).
- If LR is spilled, use BL to implement far jumps. LR is not used as a GPR
  in thumb mode so it can be clobbered if it is properly spilled / restored
  in prologue / epilogue.
- If LR is force spilled but no far jump has been emitted, try undo'ing the
  spill by:
  push lr -> delete
  pop pc -> bx lr


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33650 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2007-01-30 01:18:38 +00:00
parent 225dfe973b
commit d1b2c1e88f
3 changed files with 124 additions and 42 deletions
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132
lib/Target/ARM/ARMConstantIslandPass.cpp
View File

@ -29,7 +29,9 @@
#include <iostream>
using namespace llvm;
STATISTIC(NumSplit, "Number of uncond branches inserted");
STATISTIC(NumSplit, "Number of uncond branches inserted");
STATISTIC(NumCBrFixed, "Number of cond branches fixed");
STATISTIC(NumUBrFixed, "Number of uncond branches fixed");
namespace {
/// ARMConstantIslands - Due to limited pc-relative displacements, ARM
@ -88,7 +90,16 @@ namespace {
///
std::vector<ImmBranch> ImmBranches;
/// PushPopMIs - Keep track of all the Thumb push / pop instructions.
///
std::vector<MachineInstr*> PushPopMIs;
/// HasFarJump - True if any far jump instruction has been emitted during
/// the branch fix up pass.
bool HasFarJump;
const TargetInstrInfo *TII;
const ARMFunctionInfo *AFI;
public:
virtual bool runOnMachineFunction(MachineFunction &Fn);
@ -105,7 +116,10 @@ namespace {
void UpdateForInsertedWaterBlock(MachineBasicBlock *NewBB);
bool HandleConstantPoolUser(MachineFunction &Fn, CPUser &U);
bool BBIsInBranchRange(MachineInstr *MI, MachineBasicBlock *BB, unsigned D);
bool FixUpImmediateBranch(MachineFunction &Fn, ImmBranch &Br);
bool FixUpImmediateBr(MachineFunction &Fn, ImmBranch &Br);
bool FixUpConditionalBr(MachineFunction &Fn, ImmBranch &Br);
bool FixUpUnconditionalBr(MachineFunction &Fn, ImmBranch &Br);
bool UndoLRSpillRestore();
unsigned GetOffsetOf(MachineInstr *MI) const;
unsigned GetOffsetOf(MachineBasicBlock *MBB) const;
@ -122,7 +136,10 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &Fn) {
MachineConstantPool &MCP = *Fn.getConstantPool();
TII = Fn.getTarget().getInstrInfo();
AFI = Fn.getInfo<ARMFunctionInfo>();
HasFarJump = false;
// Renumber all of the machine basic blocks in the function, guaranteeing that
// the numbers agree with the position of the block in the function.
Fn.RenumberBlocks();
@ -142,22 +159,31 @@ bool ARMConstantIslands::runOnMachineFunction(MachineFunction &Fn) {
InitialFunctionScan(Fn, CPEMIs);
CPEMIs.clear();
// Iteratively place constant pool entries until there is no change.
bool MadeChange;
do {
MadeChange = false;
// Iteratively place constant pool entries and fix up branches until there
// is no change.
bool MadeChange = false;
while (true) {
bool Change = false;
for (unsigned i = 0, e = CPUsers.size(); i != e; ++i)
MadeChange |= HandleConstantPoolUser(Fn, CPUsers[i]);
Change |= HandleConstantPoolUser(Fn, CPUsers[i]);
for (unsigned i = 0, e = ImmBranches.size(); i != e; ++i)
MadeChange |= FixUpImmediateBranch(Fn, ImmBranches[i]);
} while (MadeChange);
Change |= FixUpImmediateBr(Fn, ImmBranches[i]);
if (!Change)
break;
MadeChange = true;
}
// 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->isLRForceSpilled() && AFI->isThumbFunction())
MadeChange |= UndoLRSpillRestore();
BBSizes.clear();
WaterList.clear();
CPUsers.clear();
ImmBranches.clear();
return true;
return MadeChange;
}
/// DoInitialPlacement - Perform the initial placement of the constant pool
@ -258,6 +284,9 @@ void ARMConstantIslands::InitialFunctionScan(MachineFunction &Fn,
ImmBranches.push_back(ImmBranch(I, MaxDisp, isCond, UOpc));
}
if (Opc == ARM::tPUSH || Opc == ARM::tPOP_RET)
PushPopMIs.push_back(I);
// Scan the instructions for constant pool operands.
for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op)
if (I->getOperand(op).isConstantPoolIndex()) {
@ -380,7 +409,6 @@ void ARMConstantIslands::UpdateForInsertedWaterBlock(MachineBasicBlock *NewBB) {
/// account for this change.
void ARMConstantIslands::SplitBlockBeforeInstr(MachineInstr *MI) {
MachineBasicBlock *OrigBB = MI->getParent();
const ARMFunctionInfo *AFI = OrigBB->getParent()->getInfo<ARMFunctionInfo>();
bool isThumb = AFI->isThumbFunction();
// Create a new MBB for the code after the OrigBB.
@ -524,32 +552,53 @@ bool ARMConstantIslands::BBIsInBranchRange(MachineInstr *MI,
return false;
}
static inline unsigned getUncondBranchDisp(int Opc) {
return (Opc == ARM::tB) ? (1<<10)*2 : (1<<23)*4;
}
/// FixUpImmediateBranch - Fix up immediate branches whose destination is too
/// far away to fit in its displacement field. If it is a conditional branch,
/// then it is converted to an inverse conditional branch + an unconditional
/// branch to the destination. If it is an unconditional branch, then it is
/// converted to a branch to a branch.
bool
ARMConstantIslands::FixUpImmediateBranch(MachineFunction &Fn, ImmBranch &Br) {
/// FixUpImmediateBr - Fix up an immediate branch whose destination is too far
/// away to fit in its displacement field.
bool ARMConstantIslands::FixUpImmediateBr(MachineFunction &Fn, ImmBranch &Br) {
MachineInstr *MI = Br.MI;
MachineBasicBlock *DestBB = MI->getOperand(0).getMachineBasicBlock();
if (BBIsInBranchRange(MI, DestBB, Br.MaxDisp))
return false;
if (!Br.isCond) {
// Unconditional branch. We have to insert a branch somewhere to perform
// a two level branch (branch to branch). FIXME: not yet implemented.
assert(false && "Can't handle unconditional branch yet!");
return false;
}
if (!Br.isCond)
return FixUpUnconditionalBr(Fn, Br);
return FixUpConditionalBr(Fn, Br);
}
// Otherwise, add a unconditional branch to the destination and
// invert the branch condition to jump over it:
/// FixUpUnconditionalBr - Fix up an unconditional branches whose destination is
/// too far away to fit in its displacement field. If LR register has been
/// spilled in the epilogue, then we can use BL to implement a far jump.
/// Otherwise, add a intermediate branch instruction to to a branch.
bool
ARMConstantIslands::FixUpUnconditionalBr(MachineFunction &Fn, ImmBranch &Br) {
MachineInstr *MI = Br.MI;
MachineBasicBlock *MBB = MI->getParent();
assert(AFI->isThumbFunction() && "Expected a Thumb function!");
// Use BL to implement far jump.
Br.MaxDisp = (1 << 21) * 2;
MI->setInstrDescriptor(TII->get(ARM::tBfar));
BBSizes[MBB->getNumber()] += 2;
HasFarJump = true;
NumUBrFixed++;
return true;
}
static inline unsigned getUncondBranchDisp(int Opc) {
return (Opc == ARM::tB) ? (1<<10)*2 : (1<<23)*4;
}
/// FixUpConditionalBr - Fix up a conditional branches whose destination is too
/// far away to fit in its displacement field. It is converted to an inverse
/// conditional branch + an unconditional branch to the destination.
bool
ARMConstantIslands::FixUpConditionalBr(MachineFunction &Fn, ImmBranch &Br) {
MachineInstr *MI = Br.MI;
MachineBasicBlock *DestBB = MI->getOperand(0).getMachineBasicBlock();
// Add a unconditional branch to the destination and invert the branch
// condition to jump over it:
// blt L1
// =>
// bge L2
@ -565,6 +614,7 @@ ARMConstantIslands::FixUpImmediateBranch(MachineFunction &Fn, ImmBranch &Br) {
MachineInstr *BackMI = &MBB->back();
bool NeedSplit = (BackMI != MI) || !BBHasFallthrough(MBB);
NumCBrFixed++;
if (BackMI != MI) {
if (next(MachineBasicBlock::iterator(MI)) == MBB->back() &&
BackMI->getOpcode() == Br.UncondBr) {
@ -606,3 +656,21 @@ ARMConstantIslands::FixUpImmediateBranch(MachineFunction &Fn, ImmBranch &Br) {
BBSizes[MBB->getNumber()] += ARM::GetInstSize(&MBB->back());
return true;
}
/// UndoLRSpillRestore - Remove Thumb push / pop instructions that only spills
/// LR / restores LR to pc.
bool ARMConstantIslands::UndoLRSpillRestore() {
bool MadeChange = false;
for (unsigned i = 0, e = PushPopMIs.size(); i != e; ++i) {
MachineInstr *MI = PushPopMIs[i];
if (MI->getNumOperands() == 1) {
if (MI->getOpcode() == ARM::tPOP_RET &&
MI->getOperand(0).getReg() == ARM::PC)
BuildMI(MI->getParent(), TII->get(ARM::tBX_RET));
MI->eraseFromParent();
MadeChange = true;
}
}
return MadeChange;
}

14
lib/Target/ARM/ARMMachineFunctionInfo.h
View File

@ -36,9 +36,9 @@ class ARMFunctionInfo : public MachineFunctionInfo {
/// processFunctionBeforeCalleeSavedScan().
bool HasStackFrame;
/// LRSpilled - True if the LR register has been spilled.
///
bool LRSpilled;
/// LRSForceSpilled - True if the LR register has been for spilled to enable
/// far jump.
bool LRForceSpilled;
/// FramePtrSpillOffset - If HasStackFrame, this records the frame pointer
/// spill stack offset.
@ -75,13 +75,13 @@ class ARMFunctionInfo : public MachineFunctionInfo {
public:
ARMFunctionInfo() :
isThumb(false),
VarArgsRegSaveSize(0), HasStackFrame(false), LRSpilled(false),
VarArgsRegSaveSize(0), HasStackFrame(false), LRForceSpilled(false),
FramePtrSpillOffset(0), GPRCS1Offset(0), GPRCS2Offset(0), DPRCSOffset(0),
GPRCS1Size(0), GPRCS2Size(0), DPRCSSize(0), JumpTableUId(0) {}
ARMFunctionInfo(MachineFunction &MF) :
isThumb(MF.getTarget().getSubtarget<ARMSubtarget>().isThumb()),
VarArgsRegSaveSize(0), HasStackFrame(false), LRSpilled(false),
VarArgsRegSaveSize(0), HasStackFrame(false), LRForceSpilled(false),
FramePtrSpillOffset(0), GPRCS1Offset(0), GPRCS2Offset(0), DPRCSOffset(0),
GPRCS1Size(0), GPRCS2Size(0), DPRCSSize(0), JumpTableUId(0) {}
@ -93,8 +93,8 @@ public:
bool hasStackFrame() const { return HasStackFrame; }
void setHasStackFrame(bool s) { HasStackFrame = s; }
bool isLRSpilled() const { return LRSpilled; }
void setLRIsSpilled(bool s) { LRSpilled = s; }
bool isLRForceSpilled() const { return LRForceSpilled; }
void setLRIsForceSpilled(bool s) { LRForceSpilled = s; }
unsigned getFramePtrSpillOffset() const { return FramePtrSpillOffset; }
void setFramePtrSpillOffset(unsigned o) { FramePtrSpillOffset = o; }

20
lib/Target/ARM/ARMRegisterInfo.cpp
View File

@ -770,17 +770,29 @@ processFunctionBeforeCalleeSavedScan(MachineFunction &MF) const {
}
ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
bool ForceLRSpill = false;
if (!LRSpilled && AFI->isThumbFunction()) {
unsigned FnSize = ARM::GetFunctionSize(MF);
// Force LR spill if the Thumb function size is > 2048. This enables the
// use of BL to implement far jump. If it turns out that it's not needed
// the branch fix up path will undo it.
if (FnSize >= (1 << 11)) {
CanEliminateFrame = false;
ForceLRSpill = true;
}
}
if (!CanEliminateFrame) {
AFI->setHasStackFrame(true);
// If LR is not spilled, but at least one of R4, R5, R6, and R7 is spilled.
// Spill LR as well so we can fold BX_RET to the registers restore (LDM).
if (!LRSpilled && CS1Spilled) {
LRSpilled = true;
MF.changePhyRegUsed(ARM::LR, true);
NumGPRSpills++;
UnspilledCS1GPRs.erase(std::find(UnspilledCS1GPRs.begin(),
UnspilledCS1GPRs.end(), (unsigned)ARM::LR));
ForceLRSpill = false;
}
if (STI.isTargetDarwin()) {
@ -800,8 +812,10 @@ processFunctionBeforeCalleeSavedScan(MachineFunction &MF) const {
}
}
// Remembe if LR has been spilled.
AFI->setLRIsSpilled(LRSpilled);
if (ForceLRSpill) {
MF.changePhyRegUsed(ARM::LR, true);
AFI->setLRIsForceSpilled(true);
}
}
/// Move iterator pass the next bunch of callee save load / store ops for