Fix bug with critical edge splitting code where it wouldn't update PHI nodes

in the old destination block to indicate that the value flows from the new
edge splitting block, not from the original multi-successor block.

llvm-svn: 3590

1 files changed, 12 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/CriticalEdge.cpp b/llvm/lib/Transforms/Utils/CriticalEdge.cpp
index 07a3a542e55..35eac3f34d6 100644
--- a/llvm/lib/Transforms/Utils/CriticalEdge.cpp
+++ b/llvm/lib/Transforms/Utils/CriticalEdge.cpp
@@ -7,6 +7,7 @@
 
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/iTerminators.h"
+#include "llvm/iPHINode.h"
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Support/CFG.h"
 
@@ -38,9 +39,9 @@ void SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
 
   // 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(TI->getSuccessor(SuccNum));
+  BranchInst *BI = new BranchInst(DestBB);
   NewBB->getInstList().push_back(BI);
   
   // Branch to the new block, breaking the edge...
@@ -50,6 +51,15 @@ void SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
   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.
   //