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//===-- Local.h - Functions to perform local transformations -----*- C++ -*--=//
//
// This family of functions perform various local transformations to the
// program.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/iTerminators.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/CFG.h"
// isCriticalEdge - Return true if the specified edge is a critical edge.
// Critical edges are edges from a block with multiple successors to a block
// with multiple predecessors.
//
bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum) {
assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
if (TI->getNumSuccessors() <= 1) return false;
const BasicBlock *Dest = TI->getSuccessor(SuccNum);
pred_const_iterator I = pred_begin(Dest), E = pred_end(Dest);
// If there is more than one predecessor, this is a critical edge...
assert(I != E && "No preds, but we have an edge to the block?");
++I; // Skip one edge due to the incoming arc from TI.
return I != E;
}
// SplitCriticalEdge - Insert a new node node to split the critical edge. This
// will update DominatorSet, ImmediateDominator and DominatorTree information if
// it is available, thus calling this pass will not invalidate either of them.
//
void SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
assert(isCriticalEdge(TI, SuccNum) &&
"Cannot break a critical edge, if it isn't a critical edge");
BasicBlock *TIBB = TI->getParent();
// Create a new basic block, linking it into the CFG.
BasicBlock *NewBB = new BasicBlock(TIBB->getName()+"_crit_edge");
// Create our unconditional branch...
BranchInst *BI = new BranchInst(TI->getSuccessor(SuccNum));
NewBB->getInstList().push_back(BI);
// Branch to the new block, breaking the edge...
TI->setSuccessor(SuccNum, NewBB);
// Insert the block into the function... right after the block TI lives in.
Function &F = *TIBB->getParent();
F.getBasicBlockList().insert(TIBB->getNext(), NewBB);
// Now if we have a pass object, update analysis information. Currently we
// update DominatorSet and DominatorTree information if it's available.
//
if (P) {
// Should we update DominatorSet information?
if (DominatorSet *DS = P->getAnalysisToUpdate<DominatorSet>()) {
// The blocks that dominate the new one are the blocks that dominate TIBB
// plus the new block itself.
DominatorSet::DomSetType DomSet = DS->getDominators(TIBB);
DomSet.insert(NewBB); // A block always dominates itself.
DS->addBasicBlock(NewBB, DomSet);
}
// Should we update ImmdediateDominator information?
if (ImmediateDominators *ID =
P->getAnalysisToUpdate<ImmediateDominators>()) {
// TIBB is the new immediate dominator for NewBB. NewBB doesn't dominate
// anything.
ID->addNewBlock(NewBB, TIBB);
}
// Should we update DominatorTree information?
if (DominatorTree *DT = P->getAnalysisToUpdate<DominatorTree>()) {
DominatorTree::Node *TINode = DT->getNode(TIBB);
// The new block is not the immediate dominator for any other nodes, but
// TINode is the immediate dominator for the new node.
//
DT->createNewNode(NewBB, TINode);
}
}
}
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