[llvm] [IndVarSimplify] Allow predicateLoopExit on some loops with local writes (PR #155901)

[Florian Mayer via llvm-commits]

================
@@ -1816,11 +1821,31 @@ bool IndVarSimplify::predicateLoopExits(Loop *L, SCEVExpander &Rewriter) {
   // suggestions on how to improve this?  I can obviously bail out for outer
   // loops, but that seems less than ideal.  MemorySSA can find memory writes,
   // is that enough for *all* side effects?
+  bool HasLocalSideEffects = false;
   for (BasicBlock *BB : L->blocks())
     for (auto &I : *BB)
       // TODO:isGuaranteedToTransfer
-      if (I.mayHaveSideEffects())
-        return false;
+      if (I.mayHaveSideEffects()) {
+        if (!LoopPredicationTraps)
+          return false;
+        HasLocalSideEffects = true;
+        if (StoreInst *SI = dyn_cast<StoreInst>(&I)) {
+          // The local could have leaked out of the function, so we need to
+          // consider atomic operations as effects.
+          // Because we need to preserve the relative order of volatile
+          // accesses, turn off this optimization if we see any of them.
+          // TODO:
+          // We could be smarter about volatile, and check whether the
+          // reordering is valid.
+          // We also could be smarter about atomic, and check whether the
+          // local has leaked.
+          if (SI->isAtomic() || SI->isVolatile() ||
----------------
fmayer wrote:

Done

https://github.com/llvm/llvm-project/pull/155901