[llvm-commits] CVS: llvm/lib/Transforms/Utils/SimplifyCFG.cpp

[Chris Lattner]

Changes in directory llvm/lib/Transforms/Utils:

SimplifyCFG.cpp updated: 1.92 -> 1.93
---
Log message:

Fix SimplifyCFG/2005-12-03-IncorrectPHIFold.ll


---
Diffs of the changes:  (+14 -8)

 SimplifyCFG.cpp |   22 ++++++++++++++--------
 1 files changed, 14 insertions(+), 8 deletions(-)


Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
diff -u llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1.92 llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1.93
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp:1.92	Mon Oct  3 18:43:43 2005
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp	Sat Dec  3 12:25:58 2005
@@ -82,7 +82,7 @@
   //
   if (isa<PHINode>(Succ->front())) {
     std::set<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
-    for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);\
+    for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
          PI != PE; ++PI)
       if (std::find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
         // Loop over all of the PHI nodes checking to see if there are
@@ -115,19 +115,25 @@
     }
   if (IsSafe) return true;
   
-  // If the PHI nodes in BB are only used by instructions in Succ, we are ok.
-  IsSafe = true;
+  // If the PHI nodes in BB are only used by instructions in Succ, we are ok if
+  // BB and Succ have no common predecessors.
   for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I) && IsSafe; ++I) {
     PHINode *PN = cast<PHINode>(I);
     for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E;
          ++UI)
-      if (cast<Instruction>(*UI)->getParent() != Succ) {
-        IsSafe = false;
-        break;
-      }
+      if (cast<Instruction>(*UI)->getParent() != Succ)
+        return false;
   }
   
-  return IsSafe;
+  // Scan the predecessor sets of BB and Succ, making sure there are no common
+  // predecessors.  Common predecessors would cause us to build a phi node with
+  // differing incoming values, which is not legal.
+  std::set<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
+  for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
+    if (BBPreds.count(*PI))
+      return false;
+    
+  return true;
 }
 
 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional