revert r84754, it isn't the right approach. Edwin, please propose

patches for fixes like this instead of committing them directly.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84799 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 60 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 1088684..9147a99 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -1985,42 +1985,6 @@ static Instruction *FoldOpIntoSelect(Instruction &Op, SelectInst *SI,
   return 0;
 }
 
-// Check whether all the operands of the PHI dominate the PHI node,
-// knowing that the PHI's operands either dominate BB, or are defined in the BB.
-static bool checkPHI(PHINode *PN, BasicBlock *BB)
-{
-  BasicBlock *phiBB = PN->getParent();
-  for (unsigned i=0;i<PN->getNumIncomingValues();i++) {
-    Instruction *I = dyn_cast<Instruction>(PN->getIncomingValue(i));
-    if (!I)
-      continue;
-    BasicBlock *pBB = I->getParent();
-    if (pBB == BB) {
-      // another PHI in same BB is always before PN (PN is last phi).
-      if (isa<PHINode>(I))
-        continue;
-      // An instruction in the same BB, and not a phi, this is after PN.
-      return false;
-    }
-    if (phiBB == BB)
-      continue;
-    // We don't have dominator info, so just check that the instruction
-    // is not defined in on of the BB on the unique path between BB and phiBB.
-    // If there is no such unique path, or pBB equals to one of the BBs on that
-    // path we know that this operand doesn't dominate the PHI node.
-    BasicBlock *B = PN->getIncomingBlock(i);
-    while ((B = B->getUniquePredecessor())) {
-      if (pBB == B)
-        return false;
-      if (B == phiBB)
-        break;
-    }
-    // No unique path -> doesn't dominate
-    if (!B)
-      return false;
-  }
-  return true;
-}
 
 /// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which
 /// has a PHI node as operand #0, see if we can fold the instruction into the
@@ -2072,13 +2036,9 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
   // Okay, we can do the transformation: create the new PHI node.
   PHINode *NewPN = PHINode::Create(I.getType(), "");
   NewPN->reserveOperandSpace(PN->getNumOperands()/2);
-  // We must the PHI node as the last PHI, because it may use one of the other
-  // PHIs.
-  BasicBlock::iterator BBIt = PN;
-  while (isa<PHINode>(BBIt)) ++BBIt;
-  InsertNewInstBefore(NewPN, *BBIt);
+  InsertNewInstBefore(NewPN, *PN);
+  NewPN->takeName(PN);
 
-  SmallVector<Instruction*, 2> tmpWorklist;
   // Next, add all of the operands to the PHI.
   if (SelectInst *SI = dyn_cast<SelectInst>(&I)) {
     // We only currently try to fold the condition of a select when it is a phi,
@@ -2098,7 +2058,7 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
         InV = SelectInst::Create(PN->getIncomingValue(i), TrueVInPred,
                                  FalseVInPred,
                                  "phitmp", NonConstBB->getTerminator());
-        tmpWorklist.push_back(cast<Instruction>(InV));
+        Worklist.Add(cast<Instruction>(InV));
       }
       NewPN->addIncoming(InV, ThisBB);
     }
@@ -2124,7 +2084,8 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
                                 NonConstBB->getTerminator());
         else
           llvm_unreachable("Unknown binop!");
-        tmpWorklist.push_back(cast<Instruction>(InV));
+        
+        Worklist.Add(cast<Instruction>(InV));
       }
       NewPN->addIncoming(InV, PN->getIncomingBlock(i));
     }
@@ -2140,26 +2101,11 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
         InV = CastInst::Create(CI->getOpcode(), PN->getIncomingValue(i), 
                                I.getType(), "phitmp", 
                                NonConstBB->getTerminator());
-        tmpWorklist.push_back(cast<Instruction>(InV));
+        Worklist.Add(cast<Instruction>(InV));
       }
       NewPN->addIncoming(InV, PN->getIncomingBlock(i));
     }
   }
-  // The PHI's operands must dominate the PHI, if we can't prove that
-  // undo this transformation.
-  if (!checkPHI(NewPN, I.getParent())) {
-    Worklist.Remove(NewPN);
-    NewPN->eraseFromParent();
-    while (!tmpWorklist.empty()) {
-      tmpWorklist.pop_back_val()->eraseFromParent();
-    }
-    return 0;
-  }
-  while (!tmpWorklist.empty()) {
-    Worklist.Add(tmpWorklist.pop_back_val());
-  }
-  NewPN->takeName(PN);
-  Worklist.Add(PN);
   return ReplaceInstUsesWith(I, NewPN);
 }