//===----------------------------------------------------------------------===//
#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"
+#include "llvm/iTerminators.h"
+#include "llvm/iPHINode.h"
+#include "llvm/Support/CFG.h"
+#include "Support/Statistic.h"
-static Statistic<> NumBroken("break-crit-edges\t- Number of blocks inserted");
+namespace {
+ Statistic<> NumBroken("break-crit-edges", "Number of blocks inserted");
-class BreakCriticalEdges : public FunctionPass {
-public:
- virtual bool runOnFunction(Function &F);
+ struct BreakCriticalEdges : public FunctionPass {
+ virtual bool runOnFunction(Function &F);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addPreserved<DominatorSet>();
+ AU.addPreserved<ImmediateDominators>();
+ AU.addPreserved<DominatorTree>();
+ AU.addPreservedID(LoopPreheadersID); // No preheaders deleted.
+ }
+ };
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addPreserved<DominatorSet>();
- AU.addPreserved<ImmediateDominators>();
- AU.addPreserved<DominatorTree>();
+ RegisterOpt<BreakCriticalEdges> X("break-crit-edges",
+ "Break critical edges in CFG");
+}
+
+// Publically exposed interface to pass...
+const PassInfo *BreakCriticalEdgesID = X.getPassInfo();
+Pass *createBreakCriticalEdgesPass() { return new BreakCriticalEdges(); }
+
+
+// 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");
+ BasicBlock *DestBB = TI->getSuccessor(SuccNum);
+ // Create our unconditional branch...
+ BranchInst *BI = new BranchInst(DestBB);
+ 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);
+
+ // If there are any PHI nodes in DestBB, we need to update them so that they
+ // merge incoming values from NewBB instead of from TIBB.
+ //
+ for (BasicBlock::iterator I = DestBB->begin();
+ PHINode *PN = dyn_cast<PHINode>(&*I); ++I) {
+ // We no longer enter through TIBB, now we come in through NewBB.
+ PN->replaceUsesOfWith(TIBB, NewBB);
}
-};
-static RegisterOpt<BreakCriticalEdges> X("break-crit-edges",
- "Break critical edges in CFG");
+ // If we don't have a pass object, we can't update anything...
+ if (P == 0) return;
-Pass *createBreakCriticalEdgesPass() { return new BreakCriticalEdges(); }
+ // Now update analysis information. These are the analyses that we are
+ // currently capable of updating...
+ //
+
+ // 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.
+ //
+ if (TINode) // Don't break unreachable code!
+ DT->createNewNode(NewBB, TINode);
+ }
+}
// runOnFunction - Loop over all of the edges in the CFG, breaking critical
// edges as they are found.
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;
- }
+ if (TI->getNumSuccessors() > 1)
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+ if (isCriticalEdge(TI, i)) {
+ SplitCriticalEdge(TI, i, this);
+ ++NumBroken;
+ Changed = true;
+ }
}
return Changed;
projects / oota-llvm.git / blobdiff