Revert "Add support for combining GEPs across PHI nodes"

This reverts commit r209755.

it was the real cause of the libc++ build failure.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209775 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 0 insertions, 79 deletions

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index 80eec1b311..4c36887f62 100644
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1220,85 +1220,6 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
     if (MadeChange) return &GEP;
   }
 
-  // Check to see if the inputs to the PHI node are getelementptr instructions.
-  if (PHINode *PN = dyn_cast<PHINode>(PtrOp)) {
-    GetElementPtrInst *Op1 = dyn_cast<GetElementPtrInst>(PN->getOperand(0));
-    if (!Op1)
-      return nullptr;
-
-    signed DI = -1;
-
-    for (auto I = PN->op_begin()+1, E = PN->op_end(); I !=E; ++I) {
-      GetElementPtrInst *Op2 = dyn_cast<GetElementPtrInst>(*I);
-      if (!Op2 || Op1->getNumOperands() != Op2->getNumOperands())
-        return nullptr;
-
-      for (unsigned J = 0, F = Op1->getNumOperands(); J != F; ++J) {
-        if (Op1->getOperand(J)->getType() != Op2->getOperand(J)->getType())
-          return nullptr;
-
-        if (Op1->getOperand(J) != Op2->getOperand(J)) {
-          if (DI == -1) {
-            // We have not seen any differences yet in the GEPs feeding the
-            // PHI yet, so we record this one if it is allowed to be a
-            // variable.
-
-            // The first two arguments can vary for any GEP, the rest have to be
-            // static for struct slots
-            if (J > 1) {
-              SmallVector<Value*, 8> Idxs(GEP.idx_begin(), GEP.idx_begin()+J);
-              Type *Ty =
-                GetElementPtrInst::getIndexedType(Op1->getOperand(0)->getType(),
-                                                  Idxs);
-              if (Ty->isStructTy())
-                return nullptr;
-            }
-
-            DI = J;
-          } else {
-            // The GEP is different by more than one input. While this could be
-            // extended to support GEPs that vary by more than one variable it
-            // doesn't make sense since it greatly increases the complexity and
-            // would result in an R+R+R addressing mode which no backend
-            // directly supports and would need to be broken into several
-            // simpler instructions anyway.
-            return nullptr;
-          }
-        }
-      }
-    }
-
-    GetElementPtrInst *NewGEP = cast<GetElementPtrInst>(Op1->clone());
-
-    if (DI == -1) {
-      // All the GEPs feeding the PHI are identical. Clone one down into our
-      // BB so that it can be merged with the current GEP.
-      GEP.getParent()->getInstList().insert(GEP.getParent()->getFirstNonPHI(),
-                                            NewGEP);
-    } else {
-      // All the GEPs feeding the PHI differ at a single offset. Clone a GEP
-      // into the current block so it can be merged, and create a new PHI to
-      // set that index.
-      Instruction *InsertPt = Builder->GetInsertPoint();
-      Builder->SetInsertPoint(PN);
-      PHINode *NewPN = Builder->CreatePHI(Op1->getOperand(DI)->getType(),
-                                          PN->getNumOperands());
-      Builder->SetInsertPoint(InsertPt);
-
-      for (auto &I : PN->operands())
-        NewPN->addIncoming(cast<GEPOperator>(I)->getOperand(DI),
-                           PN->getIncomingBlock(I));
-
-      NewGEP->setOperand(DI, NewPN);
-      GEP.getParent()->getInstList().insert(GEP.getParent()->getFirstNonPHI(),
-                                            NewGEP);
-      NewGEP->setOperand(DI, NewPN);
-    }
-
-    GEP.setOperand(0, NewGEP);
-    PtrOp = NewGEP;
-  }
-
   // Combine Indices - If the source pointer to this getelementptr instruction
   // is a getelementptr instruction, combine the indices of the two
   // getelementptr instructions into a single instruction.