diff --git a/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp b/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp
index 352a1b331001a..d7caa60055750 100644
--- a/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp
+++ b/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp
@@ -1048,7 +1048,8 @@ bool InferAddressSpacesImpl::updateAddressSpace(
   } else {
     // Otherwise, infer the address space from its pointer operands.
     SmallVector<Constant *, 2> ConstantPtrOps;
-    for (Value *PtrOperand : getPointerOperands(V, *DL, TTI)) {
+    auto PtrOps = getPointerOperands(V, *DL, TTI);
+    for (Value *PtrOperand : PtrOps) {
       auto I = InferredAddrSpace.find(PtrOperand);
       unsigned OperandAS;
       if (I == InferredAddrSpace.end()) {
@@ -1079,12 +1080,18 @@ bool InferAddressSpacesImpl::updateAddressSpace(
       if (NewAS == FlatAddrSpace)
         break;
     }
+
     if (NewAS != FlatAddrSpace && NewAS != UninitializedAddressSpace) {
       if (any_of(ConstantPtrOps, [=](Constant *C) {
             return !isSafeToCastConstAddrSpace(C, NewAS);
           }))
         NewAS = FlatAddrSpace;
     }
+
+    // operator(uninit const, uninit const, ...) -> flat
+    if (NewAS == UninitializedAddressSpace &&
+        PtrOps.size() == ConstantPtrOps.size())
+      NewAS = FlatAddrSpace;
   }
 
   unsigned OldAS = InferredAddrSpace.lookup(&V);
diff --git a/llvm/test/Transforms/InferAddressSpaces/NVPTX/nullptr.ll b/llvm/test/Transforms/InferAddressSpaces/NVPTX/nullptr.ll
new file mode 100644
index 0000000000000..516d90d282f78
--- /dev/null
+++ b/llvm/test/Transforms/InferAddressSpaces/NVPTX/nullptr.ll
@@ -0,0 +1,36 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=infer-address-spaces %s | FileCheck %s
+
+target triple = "nvptx64-unknown-nvidiacl"
+
+define ptr @pr171890() {
+; CHECK-LABEL: define ptr @pr171890() {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[STACK:%.*]] = alloca i16, align 2
+; CHECK-NEXT:    [[TMP0:%.*]] = addrspacecast ptr [[STACK]] to ptr addrspace(5)
+; CHECK-NEXT:    [[TMP1:%.*]] = addrspacecast ptr addrspace(5) [[TMP0]] to ptr
+; CHECK-NEXT:    br label %[[IF:.*]]
+; CHECK:       [[IF]]:
+; CHECK-NEXT:    [[NULLPHI:%.*]] = phi ptr [ null, %[[ENTRY]] ]
+; CHECK-NEXT:    br i1 false, label %[[THEN:.*]], label %[[ELSE:.*]]
+; CHECK:       [[ELSE]]:
+; CHECK-NEXT:    br label %[[THEN]]
+; CHECK:       [[THEN]]:
+; CHECK-NEXT:    [[PHI2:%.*]] = phi ptr [ [[TMP1]], %[[IF]] ], [ [[NULLPHI]], %[[ELSE]] ]
+; CHECK-NEXT:    ret ptr [[PHI2]]
+;
+entry:
+  %stack = alloca i16, align 2
+  br label %if
+
+if:
+  %nullphi = phi ptr [ null, %entry ]
+  br i1 false, label %then, label %else
+
+else:
+  br label %then
+
+then:
+  %phi2 = phi ptr [ %stack, %if ], [ %nullphi, %else ]
+  ret ptr %phi2
+}