Introduce llvm::SplitAllCriticalEdges

[kcc]

Summary

move the code from BreakCriticalEdges::runOnFunction()
into a separate utility function llvm::SplitAllCriticalEdges()
so that it can be used independently.
No functionality change intended.

[nlewycky]

LGTM

include/llvm/Transforms/Utils/BasicBlockUtils.h

while (1) {
     assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
     if (TI->getSuccessor(i) == Dst)
       return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges,
                                DontDeleteUselessPHIs);
     ++i;
   }
 }
 
+// SplitAllCriticalEdges - Loop over all of the edges in the CFG,
+// breaking critical edges as they are found. Pass P must not be NULL.
+// Returns the number of broken edges.
+unsigned SplitAllCriticalEdges(Function &F, Pass *P);
+
 /// SplitEdge -  Split the edge connecting specified block. Pass P must
 /// not be NULL.
 BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, Pass *P);
 
 /// SplitBlock - Split the specified block at the specified instruction - every
 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
 /// to a new block.  The two blocks are joined by an unconditional branch and
 /// the loop info is updated.

lib/Transforms/Utils/BasicBlockUtils.cpp

BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) {
 
   // Otherwise, if BB has a single successor, split it at the bottom of the
   // block.
   assert(BB->getTerminator()->getNumSuccessors() == 1 &&
          "Should have a single succ!");
   return SplitBlock(BB, BB->getTerminator(), P);
 }
 
+unsigned llvm::SplitAllCriticalEdges(Function &F, Pass *P) {
+  unsigned NumBroken = 0;
+  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
+    TerminatorInst *TI = I->getTerminator();
+    if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
+      for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+        if (SplitCriticalEdge(TI, i, P))
+          ++NumBroken;
+  }
+  return NumBroken;
+}
+
 /// SplitBlock - Split the specified block at the specified instruction - every
 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
 /// to a new block.  The two blocks are joined by an unconditional branch and
 /// the loop info is updated.
 ///
 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
   BasicBlock::iterator SplitIt = SplitPt;
   while (isa<PHINode>(SplitIt) || isa<LandingPadInst>(SplitIt))

lib/Transforms/Utils/BreakCriticalEdges.cpp

 
 namespace {
   struct BreakCriticalEdges : public FunctionPass {
     static char ID; // Pass identification, replacement for typeid
     BreakCriticalEdges() : FunctionPass(ID) {
       initializeBreakCriticalEdgesPass(*PassRegistry::getPassRegistry());
     }
 
-    bool runOnFunction(Function &F) override;
+    bool runOnFunction(Function &F) override {
+      unsigned N = SplitAllCriticalEdges(F, this);
+      NumBroken += N;
+      return N > 0;
+    }
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.addPreserved<DominatorTreeWrapperPass>();
       AU.addPreserved<LoopInfo>();
 
       // No loop canonicalization guarantees are broken by this pass.
       AU.addPreservedID(LoopSimplifyID);
     }
   };
 }
 
 char BreakCriticalEdges::ID = 0;
 INITIALIZE_PASS(BreakCriticalEdges, "break-crit-edges",
                 "Break critical edges in CFG", false, false)
 
 // Publicly exposed interface to pass...
 char &llvm::BreakCriticalEdgesID = BreakCriticalEdges::ID;
 FunctionPass *llvm::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();
-    if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
-      for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
-        if (SplitCriticalEdge(TI, i, this)) {
-          ++NumBroken;
-          Changed = true;
-        }
-  }
-
-  return Changed;
-}
-
 //===----------------------------------------------------------------------===//
 //    Implementation of the external critical edge manipulation functions
 //===----------------------------------------------------------------------===//
 
 /// createPHIsForSplitLoopExit - When a loop exit edge is split, LCSSA form
 /// may require new PHIs in the new exit block. This function inserts the
 /// new PHIs, as needed. Preds is a list of preds inside the loop, SplitBB
 /// is the new loop exit block, and DestBB is the old loop exit, now the