diff --git a/llvm/lib/Analysis/GlobalsModRef.cpp b/llvm/lib/Analysis/GlobalsModRef.cpp
--- a/llvm/lib/Analysis/GlobalsModRef.cpp
+++ b/llvm/lib/Analysis/GlobalsModRef.cpp
@@ -533,7 +533,8 @@
           FI.addModRefInfo(ModRefInfo::ModRef);
           if (!F->onlyAccessesArgMemory())
             FI.setMayReadAnyGlobal();
-          if (!F->isIntrinsic()) {
+          // Intrinsics, like any other synchronizing function, can make effects of other threads visible. Without nosync we know nothing really.
+          if (!F->hasNoSync()) {
             KnowNothing = true;
             break;
           }