diff --git a/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp b/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp
--- a/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp
@@ -104,6 +104,10 @@
           auto *UserI = cast<Instruction>(U.getUser());
           U.set(V);
 
+          // Do not bother dealing with unreachable code.
+          if (!DT.isReachableFromEntry(UserI->getParent()))
+            continue;
+
           // If the instruction is used by a PHI node we have already processed
           // we'll need to iterate on the loop body to converge, so add it to
           // the next set.
diff --git a/llvm/test/Transforms/LoopInstSimplify/pr55072.ll b/llvm/test/Transforms/LoopInstSimplify/pr55072.ll
--- a/llvm/test/Transforms/LoopInstSimplify/pr55072.ll
+++ b/llvm/test/Transforms/LoopInstSimplify/pr55072.ll
@@ -1,11 +1,16 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -S %s -passes=loop-instsimplify | FileCheck %s
 ; RUN: opt -S %s -passes='loop-mssa(loop-instsimplify)' -verify-memoryssa | FileCheck %s
 
-; XFAIL: *
-; REQUIRES: asserts
-
 define i32 @test_01() {
-; CHECK-LABEL: test_01
+; CHECK-LABEL: @test_01(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    br label [[LOOP]]
+; CHECK:       unreached:
+; CHECK-NEXT:    ret i32 0
+;
 bb:
   br label %loop