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- Do not expose Critical Edge breaking mechanics outside the BCE pass, thus
removing it from Transforms/Local.h and from Transforms/Utils/* git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3911 91177308-0d34-0410-b5e6-96231b3b80d8
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//===-- CriticalEdge.cpp - Functions to detect and split critical edges ---===//
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//
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// These functions are here to detect and split critical edges in the CFG.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/iTerminators.h"
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#include "llvm/iPHINode.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Support/CFG.h"
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// isCriticalEdge - Return true if the specified edge is a critical edge.
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// Critical edges are edges from a block with multiple successors to a block
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// with multiple predecessors.
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//
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bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum) {
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assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
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if (TI->getNumSuccessors() <= 1) return false;
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const BasicBlock *Dest = TI->getSuccessor(SuccNum);
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pred_const_iterator I = pred_begin(Dest), E = pred_end(Dest);
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// If there is more than one predecessor, this is a critical edge...
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assert(I != E && "No preds, but we have an edge to the block?");
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++I; // Skip one edge due to the incoming arc from TI.
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return I != E;
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}
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// SplitCriticalEdge - Insert a new node node to split the critical edge. This
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// will update DominatorSet, ImmediateDominator and DominatorTree information if
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// it is available, thus calling this pass will not invalidate either of them.
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//
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void SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
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assert(isCriticalEdge(TI, SuccNum) &&
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"Cannot break a critical edge, if it isn't a critical edge");
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BasicBlock *TIBB = TI->getParent();
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// Create a new basic block, linking it into the CFG.
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BasicBlock *NewBB = new BasicBlock(TIBB->getName()+"_crit_edge");
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BasicBlock *DestBB = TI->getSuccessor(SuccNum);
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// Create our unconditional branch...
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BranchInst *BI = new BranchInst(DestBB);
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NewBB->getInstList().push_back(BI);
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// Branch to the new block, breaking the edge...
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TI->setSuccessor(SuccNum, NewBB);
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// Insert the block into the function... right after the block TI lives in.
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Function &F = *TIBB->getParent();
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F.getBasicBlockList().insert(TIBB->getNext(), NewBB);
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// If there are any PHI nodes in DestBB, we need to update them so that they
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// merge incoming values from NewBB instead of from TIBB.
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//
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for (BasicBlock::iterator I = DestBB->begin();
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PHINode *PN = dyn_cast<PHINode>(&*I); ++I) {
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// We no longer enter through TIBB, now we come in through NewBB.
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PN->replaceUsesOfWith(TIBB, NewBB);
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}
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// Now if we have a pass object, update analysis information. Currently we
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// update DominatorSet and DominatorTree information if it's available.
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//
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if (P) {
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// Should we update DominatorSet information?
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if (DominatorSet *DS = P->getAnalysisToUpdate<DominatorSet>()) {
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// The blocks that dominate the new one are the blocks that dominate TIBB
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// plus the new block itself.
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DominatorSet::DomSetType DomSet = DS->getDominators(TIBB);
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DomSet.insert(NewBB); // A block always dominates itself.
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DS->addBasicBlock(NewBB, DomSet);
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}
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// Should we update ImmdediateDominator information?
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if (ImmediateDominators *ID =
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P->getAnalysisToUpdate<ImmediateDominators>()) {
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// TIBB is the new immediate dominator for NewBB. NewBB doesn't dominate
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// anything.
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ID->addNewBlock(NewBB, TIBB);
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}
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// Should we update DominatorTree information?
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if (DominatorTree *DT = P->getAnalysisToUpdate<DominatorTree>()) {
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DominatorTree::Node *TINode = DT->getNode(TIBB);
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// The new block is not the immediate dominator for any other nodes, but
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// TINode is the immediate dominator for the new node.
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//
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DT->createNewNode(NewBB, TINode);
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}
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}
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}
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