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Cleanup PPCEarlyReturn

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Some general cleanup and only scan the end of a BB for branches (once we're
done with the terminators and debug values, then there should not be any other
branches). These address post-commit review suggestions by Bill Schmidt.

No functionality change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179112 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel 2013-04-09 18:25:18 +00:00
parent 8e4df489d0
commit 13049aef8a
1 changed files with 31 additions and 28 deletions
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59
lib/Target/PowerPC/PPCInstrInfo.cpp
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@ -922,42 +922,41 @@ namespace {
const PPCInstrInfo *TII;
protected:
bool processBlock(MachineBasicBlock &LastMBB) {
bool processBlock(MachineBasicBlock &ReturnMBB) {
bool Changed = false;
MachineBasicBlock::iterator I = LastMBB.begin();
I = LastMBB.SkipPHIsAndLabels(I);
MachineBasicBlock::iterator I = ReturnMBB.begin();
I = ReturnMBB.SkipPHIsAndLabels(I);
// The block must be essentially empty except for the blr.
if (I == LastMBB.end() || I->getOpcode() != PPC::BLR ||
I != LastMBB.getLastNonDebugInstr())
if (I == ReturnMBB.end() || I->getOpcode() != PPC::BLR ||
I != ReturnMBB.getLastNonDebugInstr())
return Changed;
SmallVector<MachineBasicBlock*, 8> PredToRemove;
for (MachineBasicBlock::pred_iterator PI = LastMBB.pred_begin(),
PIE = LastMBB.pred_end(); PI != PIE; ++PI) {
for (MachineBasicBlock::pred_iterator PI = ReturnMBB.pred_begin(),
PIE = ReturnMBB.pred_end(); PI != PIE; ++PI) {
bool OtherReference = false, BlockChanged = false;
for (MachineBasicBlock::iterator J = (*PI)->begin();
J != (*PI)->end();) {
for (MachineBasicBlock::iterator J = (*PI)->getLastNonDebugInstr();;) {
if (J->getOpcode() == PPC::B) {
if (J->getOperand(0).getMBB() == &LastMBB) {
if (J->getOperand(0).getMBB() == &ReturnMBB) {
// This is an unconditional branch to the return. Replace the
// branch with a blr.
BuildMI(**PI, J, J->getDebugLoc(), TII->get(PPC::BLR));
MachineBasicBlock::iterator K = J++;
MachineBasicBlock::iterator K = J--;
K->eraseFromParent();
BlockChanged = true;
++NumBLR;
continue;
}
} else if (J->getOpcode() == PPC::BCC) {
if (J->getOperand(2).getMBB() == &LastMBB) {
if (J->getOperand(2).getMBB() == &ReturnMBB) {
// This is a conditional branch to the return. Replace the branch
// with a bclr.
BuildMI(**PI, J, J->getDebugLoc(), TII->get(PPC::BCLR))
.addImm(J->getOperand(0).getImm())
.addReg(J->getOperand(1).getReg());
MachineBasicBlock::iterator K = J++;
MachineBasicBlock::iterator K = J--;
K->eraseFromParent();
BlockChanged = true;
++NumBCLR;
@ -965,19 +964,23 @@ protected:
}
} else if (J->isBranch()) {
if (J->isIndirectBranch()) {
if (LastMBB.hasAddressTaken())
if (ReturnMBB.hasAddressTaken())
OtherReference = true;
} else
for (unsigned i = 0; i < J->getNumOperands(); ++i)
if (J->getOperand(i).isMBB() &&
J->getOperand(i).getMBB() == &LastMBB)
J->getOperand(i).getMBB() == &ReturnMBB)
OtherReference = true;
}
} else if (!J->isTerminator() && !J->isDebugValue())
break;
++J;
if (J == (*PI)->begin())
break;
--J;
}
if ((*PI)->canFallThrough() && (*PI)->isLayoutSuccessor(&LastMBB))
if ((*PI)->canFallThrough() && (*PI)->isLayoutSuccessor(&ReturnMBB))
OtherReference = true;
// Predecessors are stored in a vector and can't be removed here.
@ -990,21 +993,21 @@ protected:
}
for (unsigned i = 0, ie = PredToRemove.size(); i != ie; ++i)
PredToRemove[i]->removeSuccessor(&LastMBB);
PredToRemove[i]->removeSuccessor(&ReturnMBB);
if (Changed && !LastMBB.hasAddressTaken()) {
if (Changed && !ReturnMBB.hasAddressTaken()) {
// We now might be able to merge this blr-only block into its
// by-layout predecessor.
if (LastMBB.pred_size() == 1 &&
(*LastMBB.pred_begin())->isLayoutSuccessor(&LastMBB)) {
if (ReturnMBB.pred_size() == 1 &&
(*ReturnMBB.pred_begin())->isLayoutSuccessor(&ReturnMBB)) {
// Move the blr into the preceding block.
MachineBasicBlock &PrevMBB = **LastMBB.pred_begin();
PrevMBB.splice(PrevMBB.end(), &LastMBB, I);
PrevMBB.removeSuccessor(&LastMBB);
MachineBasicBlock &PrevMBB = **ReturnMBB.pred_begin();
PrevMBB.splice(PrevMBB.end(), &ReturnMBB, I);
PrevMBB.removeSuccessor(&ReturnMBB);
}
if (LastMBB.pred_empty())
LastMBB.eraseFromParent();
if (ReturnMBB.pred_empty())
ReturnMBB.eraseFromParent();
}
return Changed;
@ -1017,7 +1020,7 @@ public:
bool Changed = false;
// If the function does not have at least two block, then there is
// If the function does not have at least two blocks, then there is
// nothing to do.
if (MF.size() < 2)
return Changed;