diff --git a/llvm/include/llvm/IR/Intrinsics.td b/llvm/include/llvm/IR/Intrinsics.td
--- a/llvm/include/llvm/IR/Intrinsics.td
+++ b/llvm/include/llvm/IR/Intrinsics.td
@@ -518,9 +518,13 @@
 
 def int_readcyclecounter : Intrinsic<[llvm_i64_ty]>;
 
-// The assume intrinsic is marked as arbitrarily writing so that proper
-// control dependencies will be maintained.
+// The assume intrinsic is *not* marked as speculatable but without memory
+// effects. Proper control dependencies will be maintained because weakening
+// them would potentially introduce UB on paths that did not contain it before.
 def int_assume        : Intrinsic<[], [llvm_i1_ty], [IntrWillReturn,
+                                                     IntrNoMem,
+                                                     IntrNoSync,
+                                                     IntrNoFree,
                                                      NoUndef<ArgIndex<0>>]>;
 
 // Stack Protector Intrinsic - The stackprotector intrinsic writes the stack