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falling off the end of a function is ok with an unreachable instruction.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30950 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-10-14 00:21:48 +00:00
parent 78298871eb
commit 7821a8afd3
1 changed files with 57 additions and 28 deletions
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85
lib/CodeGen/BranchFolding.cpp
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@ -26,32 +26,30 @@ using namespace llvm;
namespace {
struct BranchFolder : public MachineFunctionPass {
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const { return "Branch Folder"; }
virtual const char *getPassName() const { return "Control Flow Optimizer"; }
const TargetInstrInfo *TII;
bool MadeChange;
private:
bool OptimizeBlock(MachineFunction::iterator MBB,
const TargetInstrInfo &TII);
bool isUncondBranch(const MachineInstr *MI, const TargetInstrInfo &TII) {
return TII.isBarrier(MI->getOpcode()) && TII.isBranch(MI->getOpcode());
}
bool isCondBranch(const MachineInstr *MI, const TargetInstrInfo &TII) {
return TII.isBranch(MI->getOpcode()) && !TII.isBarrier(MI->getOpcode());
}
void OptimizeBlock(MachineFunction::iterator MBB);
};
}
FunctionPass *llvm::createBranchFoldingPass() { return new BranchFolder(); }
bool BranchFolder::runOnMachineFunction(MachineFunction &MF) {
TII = MF.getTarget().getInstrInfo();
if (!TII) return false;
//MF.dump();
bool EverMadeChange = false;
bool MadeChange = true;
const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
MadeChange = true;
while (MadeChange) {
MadeChange = false;
for (MachineFunction::iterator MBB = ++MF.begin(), E = MF.end(); MBB != E;
++MBB)
MadeChange |= OptimizeBlock(MBB, TII);
OptimizeBlock(MBB);
// If branches were folded away somehow, do a quick scan and delete any dead
// blocks.
if (MadeChange) {
@ -78,13 +76,13 @@ bool BranchFolder::runOnMachineFunction(MachineFunction &MF) {
static void ReplaceUsesOfBlockWith(MachineBasicBlock *BB,
MachineBasicBlock *Old,
MachineBasicBlock *New,
const TargetInstrInfo &TII) {
const TargetInstrInfo *TII) {
assert(Old != New && "Cannot replace self with self!");
MachineBasicBlock::iterator I = BB->end();
while (I != BB->begin()) {
--I;
if (!TII.isTerminatorInstr(I->getOpcode())) break;
if (!TII->isTerminatorInstr(I->getOpcode())) break;
// Scan the operands of this machine instruction, replacing any uses of Old
// with New.
@ -103,23 +101,55 @@ static void ReplaceUsesOfBlockWith(MachineBasicBlock *BB,
}
}
bool BranchFolder::OptimizeBlock(MachineFunction::iterator MBB,
const TargetInstrInfo &TII) {
/// OptimizeBlock - Analyze and optimize control flow related to the specified
/// block. This is never called on the entry block.
void BranchFolder::OptimizeBlock(MachineFunction::iterator MBB) {
// If this block is empty, make everyone use its fall-through, not the block
// explicitly.
if (MBB->empty()) {
if (MBB->pred_empty()) return false;
MachineFunction::iterator FallThrough =next(MBB);
assert(FallThrough != MBB->getParent()->end() &&
"Fell off the end of the function!");
while (!MBB->pred_empty()) {
MachineBasicBlock *Pred = *(MBB->pred_end()-1);
ReplaceUsesOfBlockWith(Pred, MBB, FallThrough, TII);
if (MBB->pred_empty()) return; // dead block? Leave for cleanup later.
MachineFunction::iterator FallThrough = next(MBB);
if (FallThrough != MBB->getParent()->end()) {
while (!MBB->pred_empty()) {
MachineBasicBlock *Pred = *(MBB->pred_end()-1);
ReplaceUsesOfBlockWith(Pred, MBB, FallThrough, TII);
}
MadeChange = true;
}
return true;
// TODO: CHANGE STUFF TO NOT BRANCH HERE!
return;
}
// Check to see if we can simplify the terminator of the block before this
// one.
#if 0
MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
std::vector<MachineOperand> PriorCond;
if (!TII->AnalyzeBranch(*prior(MBB), PriorTBB, PriorFBB, PriorCond)) {
// If the previous branch is conditional and both conditions go to the same
// destination, remove the branch, replacing it with an unconditional one.
if (PriorTBB && PriorTBB == PriorFBB) {
TII->RemoveBranch(*prior(MBB));
PriorCond.clear();
if (PriorTBB != &*MBB)
TII->InsertBranch(*prior(MBB), PriorTBB, 0, PriorCond);
MadeChange = true;
return OptimizeBlock(MBB);
}
// If the previous branch *only* branches to *this* block (conditional or
// not) remove the branch.
if (PriorTBB == &*MBB && PriorFBB == 0) {
TII->RemoveBranch(*prior(MBB));
MadeChange = true;
return OptimizeBlock(MBB);
}
}
#endif
#if 0
if (MBB->pred_size() == 1) {
@ -235,5 +265,4 @@ bool BranchFolder::OptimizeBlock(MachineFunction::iterator MBB,
}
}
#endif
return false;
}