Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -7443,6 +7443,10 @@
   DB = &DB_;
   ORE = &ORE_;
 
+  // Do not vectorize functions when the target should be fuzzed.
+  if (F.hasFnAttribute(Attribute::OptForFuzzing))
+    return false;
+
   // Don't attempt if
   // 1. the target claims to have no vector registers, and
   // 2. interleaving won't help ILP.
Index: test/Transforms/LoopVectorize/opt-for-fuzzing.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopVectorize/opt-for-fuzzing.ll
@@ -0,0 +1,31 @@
+; RUN: opt < %s -loop-vectorize -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; CHECK-NOT: vector.body
+
+define i8 @foo(i1 %c, i32 %x, i32 %n) optforfuzzing {
+entry:
+  br label %for.body
+
+for.body:
+  %i = phi i32 [ 0, %entry ], [ %i.next, %if.end ]
+  %r = phi i32 [ 0, %entry ], [ %r.next, %if.end ]
+  br i1 %c, label %if.then, label %if.end
+
+if.then:
+  %tmp0 = sdiv i32 undef, undef
+  br label %if.end
+
+if.end:
+  %tmp1 = and i32 %r, 255
+  %i.next = add nsw i32 %i, 1
+  %r.next = add nuw nsw i32 %tmp1, %x
+  %cond = icmp eq i32 %i.next, %n
+  br i1 %cond, label %for.end, label %for.body
+
+for.end:
+  %tmp2 = phi i32 [ %r.next, %if.end ]
+  %tmp3 = trunc i32 %tmp2 to i8
+  ret i8 %tmp3
+}