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Refactor some checks into shouldTailDuplicate. Update comments. 

No functionality change.

llvm-svn: 132798
This commit is contained in:
Rafael Espindola 2011-06-09 19:54:42 +00:00
parent 729c35b680
commit 73f93930e0
1 changed files with 29 additions and 18 deletions
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47
llvm/lib/CodeGen/TailDuplication.cpp
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@ -91,6 +91,8 @@ namespace {
SmallVector<MachineBasicBlock*, 8> &TDBBs,
SmallSetVector<MachineBasicBlock*, 8> &Succs);
bool TailDuplicateBlocks(MachineFunction &MF);
bool shouldTailDuplicate(const MachineFunction &MF,
MachineBasicBlock &TailBB);
bool TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
SmallVector<MachineBasicBlock*, 8> &TDBBs,
SmallVector<MachineInstr*, 16> &Copies);
@ -184,10 +186,6 @@ bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) {
if (NumTails == TailDupLimit)
break;
// Only duplicate blocks that end with unconditional branches.
if (MBB->canFallThrough())
continue;
// Save the successors list.
SmallSetVector<MachineBasicBlock*, 8> Succs(MBB->succ_begin(),
MBB->succ_end());
@ -450,14 +448,15 @@ TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead,
}
}
/// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
/// of its predecessors.
/// shouldTailDuplicate - Determine if it is profitable to duplicate this block.
bool
TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
SmallVector<MachineBasicBlock*, 8> &TDBBs,
SmallVector<MachineInstr*, 16> &Copies) {
// Set the limit on the number of instructions to duplicate, with a default
// of one less than the tail-merge threshold. When optimizing for size,
TailDuplicatePass::shouldTailDuplicate(const MachineFunction &MF,
MachineBasicBlock &TailBB) {
// Only duplicate blocks that end with unconditional branches.
if (TailBB.canFallThrough())
return false;
// Set the limit on the cost to duplicate. When optimizing for size,
// duplicate only one, because one branch instruction can be eliminated to
// compensate for the duplication.
unsigned MaxDuplicateCount;
@ -468,12 +467,12 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
MaxDuplicateCount = TailDuplicateSize;
if (PreRegAlloc) {
if (TailBB->empty())
if (TailBB.empty())
return false;
const TargetInstrDesc &TID = TailBB->back().getDesc();
const TargetInstrDesc &TID = TailBB.back().getDesc();
// Pre-regalloc tail duplication hurts compile time and doesn't help
// much except for indirect branches and returns.
if (!TID.isIndirectBranch() && !TID.isReturn())
// much except for indirect branches.
if (!TID.isIndirectBranch())
return false;
// If the target has hardware branch prediction that can handle indirect
// branches, duplicating them can often make them predictable when there
@ -484,15 +483,15 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
}
// Don't try to tail-duplicate single-block loops.
if (TailBB->isSuccessor(TailBB))
if (TailBB.isSuccessor(&TailBB))
return false;
// Check the instructions in the block to determine whether tail-duplication
// is invalid or unlikely to be profitable.
unsigned InstrCount = 0;
bool HasCall = false;
for (MachineBasicBlock::iterator I = TailBB->begin();
I != TailBB->end(); ++I) {
for (MachineBasicBlock::const_iterator I = TailBB.begin(); I != TailBB.end();
++I) {
// Non-duplicable things shouldn't be tail-duplicated.
if (I->getDesc().isNotDuplicable()) return false;
// Do not duplicate 'return' instructions if this is a pre-regalloc run.
@ -512,6 +511,18 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
if (InstrCount > 1 && (PreRegAlloc && HasCall))
return false;
return true;
}
/// TailDuplicate - If it is profitable, duplicate TailBB's contents in each
/// of its predecessors.
bool
TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF,
SmallVector<MachineBasicBlock*, 8> &TDBBs,
SmallVector<MachineInstr*, 16> &Copies) {
if (!shouldTailDuplicate(MF, *TailBB))
return false;
DEBUG(dbgs() << "\n*** Tail-duplicating BB#" << TailBB->getNumber() << '\n');
// Iterate through all the unique predecessors and tail-duplicate this