Revert "Claim NoAlias if two GEPs index different fields of the same struct"

This reverts commit 2d5d6493f43eb68493a3852b8c226ac9fafdc7eb.

llvm-svn: 271422

1 files changed, 2 insertions, 36 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index b136c085428..cfb73541820 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -834,42 +834,8 @@ static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1,
   // Try to determine whether GEP1 and GEP2 index through arrays, into structs,
   // such that the struct field accesses provably cannot alias.
   // We also need at least two indices (the pointer, and the struct field).
-  if (GEP1->getNumIndices() < 2)
-    return MayAlias;
-
-  // If both GEP1 and GEP2 have the inbounds keyword but index different fields
-  // of the same struct, they do not alias.
-  if (GEP1->isInBounds() && GEP2->isInBounds()) {
-    auto Opi1 = GEP1->op_begin() + 1;
-    auto Opi2 = GEP2->op_begin() + 1;
-    auto Ope1 = GEP1->op_end();
-    auto Ope2 = GEP2->op_end();
-
-    SmallVector<Value *, 8> IntermediateIndices;
-    ConstantInt *C1 = nullptr;
-    ConstantInt *C2 = nullptr;
-    while (Opi1 != Ope1 && Opi2 != Ope2 &&
-           (C1 = dyn_cast<ConstantInt>(*Opi1)) &&
-           (C2 = dyn_cast<ConstantInt>(*Opi2))) {
-      if (C1 == C2) {
-        IntermediateIndices.push_back(C1);
-        ++Opi1;
-        ++Opi2;
-      } else {
-        // Both GEPs share the same pointer operand and access through the same
-        // indices up to this point, but now they are having different index
-        // values. At this point, if the indexed type is a StructType, this means
-        // that two GEPs are for two different fields in the same structure.
-        auto *Ty = GetElementPtrInst::getIndexedType(
-            GEP1->getSourceElementType(), IntermediateIndices);
-        if (isa<StructType>(Ty))
-          return NoAlias;
-        break;
-      }
-    }
-  }
-
-  if (GEP1->getNumIndices() != GEP2->getNumIndices())
+  if (GEP1->getNumIndices() != GEP2->getNumIndices() ||
+      GEP1->getNumIndices() < 2)
     return MayAlias;
 
   // If we don't know the size of the accesses through both GEPs, we can't