Index: llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
--- llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp.orig
+++ llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -339,6 +339,11 @@ bool LoopIdiomRecognize::runOnLoop(Loop *L) {
       Name == "wcslen")
     return false;
 
+  // Also disable loop idiom recognition for internal names we use in OpenBSD
+  if (Name == "_libc_memset" || Name == "_libc_memcpy" ||
+      Name == "_libc_strlen" || Name == "_libc_wcslen")
+    return false;
+
   // Determine if code size heuristics need to be applied.
   ApplyCodeSizeHeuristics =
       L->getHeader()->getParent()->hasOptSize() && UseLIRCodeSizeHeurs;
