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Make branch folding behave in the presence of landing pads.

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llvm-svn: 34476
This commit is contained in:
Jim Laskey 2007-02-21 22:42:20 +00:00
parent 1ac1a19f01
commit b56b6a7042
1 changed files with 30 additions and 25 deletions
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55
lib/CodeGen/BranchFolding.cpp
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@ -67,7 +67,8 @@ FunctionPass *llvm::createBranchFoldingPass() { return new BranchFolder(); }
/// RemoveDeadBlock - Remove the specified dead machine basic block from the
/// function, updating the CFG.
void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
assert(MBB->pred_empty() && "MBB must be dead!");
assert(!MBB->isAccessable() && "MBB must be dead!");
DOUT << "\nRemoving MBB: " << *MBB;
MachineFunction *MF = MBB->getParent();
// drop all successors.
@ -439,7 +440,7 @@ bool BranchFolder::OptimizeBranches(MachineFunction &MF) {
OptimizeBlock(MBB);
// If it is dead, remove it.
if (MBB->pred_empty()) {
if (!MBB->isAccessable()) {
RemoveDeadBlock(MBB);
MadeChange = true;
++NumDeadBlocks;
@ -485,6 +486,8 @@ static bool CorrectExtraCFGEdges(MachineBasicBlock &MBB,
} else if (*SI == DestB) {
DestB = 0;
++SI;
} else if ((*SI)->isLandingPad()) {
++SI;
} else {
// Otherwise, this is a superfluous edge, remove it.
MBB.removeSuccessor(SI);
@ -615,14 +618,14 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
// explicitly.
if (MBB->empty()) {
// Dead block? Leave for cleanup later.
if (MBB->pred_empty()) return;
if (!MBB->isAccessable()) return;
if (FallThrough == MBB->getParent()->end()) {
// TODO: Simplify preds to not branch here if possible!
} else {
// Rewrite all predecessors of the old block to go to the fallthrough
// instead.
while (!MBB->pred_empty()) {
while (MBB->isAccessable()) {
MachineBasicBlock *Pred = *(MBB->pred_end()-1);
ReplaceUsesOfBlockWith(Pred, MBB, FallThrough, TII);
}
@ -855,28 +858,30 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
bool CurFallsThru = CanFallThrough(MBB, CurUnAnalyzable, CurTBB, CurFBB,
CurCond);
// Check all the predecessors of this block. If one of them has no fall
// throughs, move this block right after it.
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
E = MBB->pred_end(); PI != E; ++PI) {
// Analyze the branch at the end of the pred.
MachineBasicBlock *PredBB = *PI;
MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough;
if (PredBB != MBB && !CanFallThrough(PredBB)
&& (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
// If the current block doesn't fall through, just move it.
// If the current block can fall through and does not end with a
// conditional branch, we need to append an unconditional jump to
// the (current) next block. To avoid a possible compile-time
// infinite loop, move blocks only backward in this case.
if (CurFallsThru) {
MachineBasicBlock *NextBB = next(MachineFunction::iterator(MBB));
CurCond.clear();
TII->InsertBranch(*MBB, NextBB, 0, CurCond);
if (!MBB->isLandingPad()) {
// Check all the predecessors of this block. If one of them has no fall
// throughs, move this block right after it.
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
E = MBB->pred_end(); PI != E; ++PI) {
// Analyze the branch at the end of the pred.
MachineBasicBlock *PredBB = *PI;
MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough;
if (PredBB != MBB && !CanFallThrough(PredBB)
&& (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
// If the current block doesn't fall through, just move it.
// If the current block can fall through and does not end with a
// conditional branch, we need to append an unconditional jump to
// the (current) next block. To avoid a possible compile-time
// infinite loop, move blocks only backward in this case.
if (CurFallsThru) {
MachineBasicBlock *NextBB = next(MachineFunction::iterator(MBB));
CurCond.clear();
TII->InsertBranch(*MBB, NextBB, 0, CurCond);
}
MBB->moveAfter(PredBB);
MadeChange = true;
return OptimizeBlock(MBB);
}
MBB->moveAfter(PredBB);
MadeChange = true;
return OptimizeBlock(MBB);
}
}