[llvm-commits] CVS: llvm/lib/Transforms/Scalar/BreakCriticalEdges.cpp

[Chris Lattner]

Changes in directory llvm/lib/Transforms/Scalar:

BreakCriticalEdges.cpp updated: 1.2 -> 1.3

---
Log message:

 - Do not expose Critical Edge breaking mechanics outside the BCE pass, thus
   removing it from Transforms/Local.h and from Transforms/Utils/*


---
Diffs of the changes:

Index: llvm/lib/Transforms/Scalar/BreakCriticalEdges.cpp
diff -u llvm/lib/Transforms/Scalar/BreakCriticalEdges.cpp:1.2 llvm/lib/Transforms/Scalar/BreakCriticalEdges.cpp:1.3
--- llvm/lib/Transforms/Scalar/BreakCriticalEdges.cpp:1.2	Tue Sep 24 10:43:12 2002
+++ llvm/lib/Transforms/Scalar/BreakCriticalEdges.cpp	Tue Sep 24 10:51:56 2002
@@ -9,10 +9,11 @@
 //===----------------------------------------------------------------------===//
 
 #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 "llvm/iTerminators.h"
+#include "llvm/iPHINode.h"
+#include "llvm/Support/CFG.h"
 #include "Support/StatisticReporter.h"
 
 namespace {
@@ -32,10 +33,93 @@
                                     "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.
+//
+static bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum) {
+  assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
+  assert (TI->getNumSuccessors() > 1);
+
+  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.
+//
+static 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);
+  }
+
+  // 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);
+    }
+  }
+}
+
 // runOnFunction - Loop over all of the edges in the CFG, breaking critical
 // edges as they are found.
 //
@@ -43,12 +127,13 @@
   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;