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Implement deletion of dead blocks, currently disabled.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26285 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-02-18 02:42:34 +00:00
parent b0d04a7dea
commit db41024a85
1 changed files with 74 additions and 27 deletions
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101
lib/Transforms/Scalar/LoopUnswitch.cpp
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@ -82,8 +82,8 @@ namespace {
BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt); BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt);
void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,Constant *Val, void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,Constant *Val,
bool isEqual); bool isEqual);
bool TryToRemoveEdge(TerminatorInst *TI, unsigned SuccNo, void RemoveBlockIfDead(BasicBlock *BB,
std::vector<Instruction*> &Worklist); std::vector<Instruction*> &Worklist);
}; };
RegisterOpt<LoopUnswitch> X("loop-unswitch", "Unswitch loops"); RegisterOpt<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
} }
@ -718,24 +718,68 @@ static void ReplaceUsesOfWith(Instruction *I, Value *V,
++NumSimplify; ++NumSimplify;
} }
/// TryToRemoveEdge - Determine whether this is a case where we're smart enough /// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
/// to remove the specified edge from the CFG and know how to update loop /// information, and remove any dead successors it has.
/// information. If it is, update SSA and the loop information for the future ///
/// change, then return true. If not, return false. void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
bool LoopUnswitch::TryToRemoveEdge(TerminatorInst *TI, unsigned DeadSuccNo, std::vector<Instruction*> &Worklist) {
std::vector<Instruction*> &Worklist) { if (pred_begin(BB) != pred_end(BB)) return; // not dead.
BasicBlock *BB = TI->getParent(), *Succ = TI->getSuccessor(DeadSuccNo);
Loop *BBLoop = LI->getLoopFor(BB);
Loop *SuccLoop = LI->getLoopFor(Succ);
// If this edge is not in a loop, or if this edge is leaving a loop to a DEBUG(std::cerr << "Nuking dead block: " << *BB);
// non-loop area, this is trivial.
if (SuccLoop == 0) { // Remove the instructions in the basic block from the worklist.
Succ->removePredecessor(BB, true); for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
return true; RemoveFromWorklist(I, Worklist);
// If this is the header block for a loop, remove the loop and all subloops.
// We leave all of the blocks that used to be part of this loop in the parent
// loop if any.
if (Loop *BBLoop = LI->getLoopFor(BB)) {
if (BBLoop->getHeader() == BB) {
if (Loop *ParentLoop = BBLoop->getParentLoop()) { // not a top-level loop.
for (Loop::iterator I = ParentLoop->begin(), E = ParentLoop->end();;
++I) {
assert(I != E && "Couldn't find loop");
if (*I == BBLoop) {
ParentLoop->removeChildLoop(I);
break;
}
}
} else {
for (LoopInfo::iterator I = LI->begin(), E = LI->end();; ++I) {
assert(I != E && "Couldn't find loop");
if (*I == BBLoop) {
LI->removeLoop(I);
break;
}
}
}
delete BBLoop;
}
}
// Remove the block from the loop info, which removes it from any loops it
// was in.
LI->removeBlock(BB);
// Remove phi node entries in successors for this block.
TerminatorInst *TI = BB->getTerminator();
std::vector<BasicBlock*> Succs;
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
Succs.push_back(TI->getSuccessor(i));
TI->getSuccessor(i)->removePredecessor(BB);
} }
return false; // Unique the successors.
std::sort(Succs.begin(), Succs.end());
Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
// Remove the basic block, including all of the instructions contained in it.
BB->eraseFromParent();
for (unsigned i = 0, e = Succs.size(); i != e; ++i)
RemoveBlockIfDead(Succs[i], Worklist);
} }
// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
@ -895,17 +939,20 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
LI->removeBlock(Succ); LI->removeBlock(Succ);
Succ->eraseFromParent(); Succ->eraseFromParent();
++NumSimplify; ++NumSimplify;
break;
} else if (ConstantBool *CB = dyn_cast<ConstantBool>(BI->getCondition())){ } else if (ConstantBool *CB = dyn_cast<ConstantBool>(BI->getCondition())){
// Conditional branch. break; // FIXME: disabled
if (TryToRemoveEdge(BI, CB->getValue(), Worklist)) { // Conditional branch. Turn it into an unconditional branch, then
DEBUG(std::cerr << "Folded branch: " << *BI); // remove dead blocks.
new BranchInst(BI->getSuccessor(!CB->getValue()), BI); DEBUG(std::cerr << "Folded branch: " << *BI);
BI->eraseFromParent(); BasicBlock *DeadSucc = BI->getSuccessor(CB->getValue());
RemoveFromWorklist(BI, Worklist); BasicBlock *LiveSucc = BI->getSuccessor(!CB->getValue());
++NumSimplify; DeadSucc->removePredecessor(BI->getParent(), true);
break; Worklist.push_back(new BranchInst(LiveSucc, BI));
} BI->eraseFromParent();
RemoveFromWorklist(BI, Worklist);
++NumSimplify;
RemoveBlockIfDead(DeadSucc, Worklist);
} }
break; break;
} }