diff --git a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
index 86411320ab248..bcff9a72b6572 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -143,6 +143,10 @@ bool InstCombinerImpl::foldIntegerTypedPHI(PHINode &PN) {
     BasicBlock *BB = std::get<0>(Incoming);
     Value *Arg = std::get<1>(Incoming);
 
+    // Arg could be a constant, constant expr, etc., which we don't cover here.
+    if (!isa<Instruction>(Arg) && !isa<Argument>(Arg))
+      return false;
+
     // First look backward:
     if (auto *PI = dyn_cast<PtrToIntInst>(Arg)) {
       AvailablePtrVals.emplace_back(PI->getOperand(0));
diff --git a/llvm/test/Transforms/InstCombine/phi-int-users.ll b/llvm/test/Transforms/InstCombine/phi-int-users.ll
new file mode 100644
index 0000000000000..6c98cc8a1c900
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/phi-int-users.ll
@@ -0,0 +1,44 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S < %s -passes=instcombine | FileCheck %s
+
+; Verify that instcombine doesn't look at users of Constant in different
+; functions for dominates() queries.
+
+define void @f1(i1 %a) {
+; CHECK-LABEL: define void @f1(
+; CHECK-SAME: i1 [[A:%.*]]) {
+; CHECK-NEXT:    br label %[[BB1:.*]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    br i1 [[A]], label %[[BB3:.*]], label %[[BB2:.*]]
+; CHECK:       [[BB2]]:
+; CHECK-NEXT:    br label %[[BB3]]
+; CHECK:       [[BB3]]:
+; CHECK-NEXT:    [[PHI:%.*]] = phi i64 [ 0, %[[BB2]] ], [ 1, %[[BB1]] ]
+; CHECK-NEXT:    [[INTTOPTR:%.*]] = inttoptr i64 [[PHI]] to ptr
+; CHECK-NEXT:    store i32 0, ptr [[INTTOPTR]], align 4
+; CHECK-NEXT:    br label %[[BB1]]
+;
+  br label %bb1
+
+bb1:
+  br i1 %a, label %bb3, label %bb2
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi = phi i64 [ 0, %bb2 ], [ 1, %bb1 ]
+  %inttoptr = inttoptr i64 %phi to ptr
+  store i32 0, ptr %inttoptr, align 4
+  br label %bb1
+}
+
+define void @f2() {
+; CHECK-LABEL: define void @f2() {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    ret void
+;
+bb:
+  %inttoptr = inttoptr i64 0 to ptr
+  ret void
+}