[flang-commits] [flang] [flang][fir] do not move alloca outside parallel regions in StackArrays (PR #218679)

[Slava Zakharin via flang-commits]

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@@ -492,13 +492,48 @@ llvm::LogicalResult fir::AllocMemConversion::matchAndRewrite(
   return mlir::success();
 }
 
-static bool isInLoop(mlir::Block *block) {
-  return mlir::LoopLikeOpInterface::blockIsInLoop(block);
+/// Return true if \p block can reach itself, i.e. it belongs to a control flow
+/// graph loop. This mirrors the control flow graph part of
+/// mlir::LoopLikeOpInterface::blockIsInLoop, which cannot be used here because
+/// it also walks the parent operations (see isInStackGrowingLoop).
+static bool isInCFGLoop(mlir::Block *block) {
+  llvm::DenseSet<mlir::Block *> visited;
+  llvm::SmallVector<mlir::Block *> stack{block};
+  while (!stack.empty()) {
+    mlir::Block *current = stack.pop_back_val();
+    auto [it, inserted] = visited.insert(current);
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vzakhari wrote:

nit: I wonder if some compilers will warn `it` as unused variable.

https://github.com/llvm/llvm-project/pull/218679