diff --git a/llvm/lib/Analysis/TargetLibraryInfo.cpp b/llvm/lib/Analysis/TargetLibraryInfo.cpp
--- a/llvm/lib/Analysis/TargetLibraryInfo.cpp
+++ b/llvm/lib/Analysis/TargetLibraryInfo.cpp
@@ -734,13 +734,8 @@
   // SizeTTy based on DataLayout and getIntPtrType isn't always valid.
   Type *SizeTTy = DL ? DL->getIntPtrType(Ctx, /*AddressSpace=*/0) : nullptr;
   auto IsSizeTTy = [SizeTTy](Type *Ty) {
-    // FIXME: For uknown historical reasons(?) we use a relaxed condition saying
-    // that any integer type may size_t, for example if we got no
-    // DataLayout. This seems like a potentially error prone relaxation (or why
-    // should we only be more strict and checking the exact type when we have a
-    // DataLayout?).
     if (!SizeTTy)
-      return Ty->isIntegerTy();
+      return false;
     return Ty == SizeTTy;
   };
   unsigned NumParams = FTy.getNumParams();