[llvm] [ValueTracking] Conservative nosync check prevents vectorization (PR #181345)

[Nikita Popov via llvm-commits]

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@@ -716,10 +716,18 @@ bool llvm::willNotFreeBetween(const Instruction *Assume,
     return true;
   };
 
-  // Make sure the current function cannot arrange for another thread to free on
-  // its behalf.
-  if (!CtxI->getFunction()->hasNoSync())
-    return false;
+  // Helper to make sure the current function cannot arrange for
+  // another thread to free on its behalf.
+  auto hasNoSyncCalls = [](auto Range) {
+    for (const auto &[Idx, I] : enumerate(Range)) {
+      if (Idx > MaxInstrsToCheckForFree)
+        return false;
+      if (const auto *CB = dyn_cast<CallBase>(&I))
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nikic wrote:

You can't just ignore non-call instructions here, they can be synchronizing (like atomic load/store).

https://github.com/llvm/llvm-project/pull/181345