diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1667,7 +1667,7 @@
     // to an index of zero, so replace it with zero if it is not zero already.
     Type *EltTy = GTI.getIndexedType();
     if (EltTy->isSized() && DL.getTypeAllocSize(EltTy) == 0)
-      if (!isa<Constant>(*I) || !cast<Constant>(*I)->isNullValue()) {
+      if (!isa<Constant>(*I) || !match(I->get(), m_Zero())) {
         *I = Constant::getNullValue(NewIndexType);
         MadeChange = true;
       }
diff --git a/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll b/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
--- a/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
+++ b/llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
@@ -651,3 +651,20 @@
   %r = extractelement <2 x i32*> %w, i32 0
   ret i32* %r
 }
+
+@global = external global [0 x i32], align 4
+
+; Make sure we don't get stuck in a loop turning the zeroinitializer into
+; <0, undef, undef, undef> and then changing it back.
+define i32* @zero_sized_type_extract(<4 x i64> %arg, i64 %arg1) {
+; CHECK-LABEL: @zero_sized_type_extract(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[TMP:%.*]] = getelementptr inbounds [0 x i32], <4 x [0 x i32]*> <[0 x i32]* @global, [0 x i32]* undef, [0 x i32]* undef, [0 x i32]* undef>, <4 x i64> <i64 0, i64 undef, i64 undef, i64 undef>, <4 x i64> [[ARG:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <4 x i32*> [[TMP]], i64 0
+; CHECK-NEXT:    ret i32* [[TMP2]]
+;
+bb:
+  %tmp = getelementptr inbounds [0 x i32], <4 x [0 x i32]*> <[0 x i32]* @global, [0 x i32]* @global, [0 x i32]* @global, [0 x i32]* @global>, <4 x i64> zeroinitializer, <4 x i64> %arg
+  %tmp2 = extractelement <4 x i32*> %tmp, i64 0
+  ret i32* %tmp2
+}