Fix constant folding of constant vector GEPs with undef or null as pointer argument.

[eddyb]

LGTM

lib/IR/ConstantFold.cpp

static Constant *ConstantFoldGetElementPtrImpl(Type *PointeeTy, Constant *C,
                                                bool inBounds,
                                                ArrayRef<IndexTy> Idxs) {
   if (Idxs.empty()) return C;
   Constant *Idx0 = cast<Constant>(Idxs[0]);
   if ((Idxs.size() == 1 && Idx0->isNullValue()))
     return C;
 
   if (isa<UndefValue>(C)) {
-    PointerType *PtrTy = cast<PointerType>(C->getType());
-    Type *Ty = GetElementPtrInst::getIndexedType(
-        cast<PointerType>(PtrTy->getScalarType())->getElementType(), Idxs);
+    PointerType *PtrTy = cast<PointerType>(C->getType()->getScalarType());
+    Type *Ty = GetElementPtrInst::getIndexedType(PtrTy->getElementType(), Idxs);
     assert(Ty && "Invalid indices for GEP!");
-    return UndefValue::get(PointerType::get(Ty, PtrTy->getAddressSpace()));
+    Type *GEPTy = PointerType::get(Ty, PtrTy->getAddressSpace());
+    if (VectorType *VT = dyn_cast<VectorType>(C->getType()))
+      GEPTy = VectorType::get(GEPTy, VT->getNumElements());
+    return UndefValue::get(GEPTy);
   }
 
   if (C->isNullValue()) {
     bool isNull = true;
     for (unsigned i = 0, e = Idxs.size(); i != e; ++i)
       if (!cast<Constant>(Idxs[i])->isNullValue()) {
         isNull = false;
         break;
       }
     if (isNull) {
-      PointerType *PtrTy = cast<PointerType>(C->getType());
-      Type *Ty = GetElementPtrInst::getIndexedType(
-          cast<PointerType>(PtrTy->getScalarType())->getElementType(), Idxs);
+      PointerType *PtrTy = cast<PointerType>(C->getType()->getScalarType());
+      Type *Ty =
+          GetElementPtrInst::getIndexedType(PtrTy->getElementType(), Idxs);
       assert(Ty && "Invalid indices for GEP!");
-      return ConstantPointerNull::get(PointerType::get(Ty,
-                                                       PtrTy->getAddressSpace()));
+      Type *GEPTy = PointerType::get(Ty, PtrTy->getAddressSpace());
+      if (VectorType *VT = dyn_cast<VectorType>(C->getType()))
+        GEPTy = VectorType::get(GEPTy, VT->getNumElements());
+      return Constant::getNullValue(GEPTy);
     }
   }
 
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
     // 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.
     //

test/Assembler/ConstantExprFold.ll

 global i1 icmp slt (i32* getelementptr (%Ty, %Ty* @B, i64 0, i32 0), 
                    i32* getelementptr (%Ty, %Ty* @B, i64 0, i32 1))            ; true
 ;global i1 icmp ne (i64* @A, i64* bitcast (%Ty* @B to i64*))                 ; true
 
 ; PR2206
 @cons = weak global i32 0, align 8              ; <i32*> [#uses=1]
 global i64 and (i64 ptrtoint (i32* @cons to i64), i64 7)
 
+global <2 x i8*> getelementptr(i8, <2 x i8*> undef, <2 x i64> <i64 1, i64 1>)
+global <2 x i8*> getelementptr({ i8 }, <2 x { i8 }*> undef, <2 x i64> <i64 1, i64 1>, <2 x i32> <i32 0, i32 0>)
+global <2 x i8*> getelementptr(i8, <2 x i8*> zeroinitializer, <2 x i64> <i64 0, i64 0>)
+global <2 x i8*> getelementptr({ i8 }, <2 x { i8 }*> zeroinitializer, <2 x i64> <i64 0, i64 0>, <2 x i32> <i32 0, i32 0>)