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//===- BreakCriticalEdges.cpp - Critical Edge Elimination Pass ------------===//
//
// BreakCriticalEdges pass - Break all of the critical edges in the CFG by
// inserting a dummy basic block. This pass may be "required" by passes that
// cannot deal with critical edges. For this usage, the structure type is
// forward declared. This pass obviously invalidates the CFG, but can update
// forward dominator (set, immediate dominators, and tree) information.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Function.h"
#include "llvm/InstrTypes.h"
#include "Support/StatisticReporter.h"
static Statistic<> NumBroken("break-crit-edges\t- Number of blocks inserted");
class BreakCriticalEdges : public FunctionPass {
public:
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreserved<DominatorSet>();
AU.addPreserved<ImmediateDominators>();
AU.addPreserved<DominatorTree>();
}
};
static RegisterOpt<BreakCriticalEdges> X("break-crit-edges",
"Break critical edges in CFG");
Pass *createBreakCriticalEdgesPass() { return new BreakCriticalEdges(); }
// runOnFunction - Loop over all of the edges in the CFG, breaking critical
// edges as they are found.
//
bool BreakCriticalEdges::runOnFunction(Function &F) {
bool Changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
TerminatorInst *TI = I->getTerminator();
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
if (isCriticalEdge(TI, i)) {
SplitCriticalEdge(TI, i, this);
++NumBroken;
Changed = true;
}
}
return Changed;
}