[llvm-branch-commits] [flang] [flang][OpenMP] Handle "loop-local values" in `do concurrent` nests (PR #127635)

[Sergio Afonso via llvm-branch-commits]

================
@@ -361,6 +361,64 @@ void sinkLoopIVArgs(mlir::ConversionPatternRewriter &rewriter,
     ++idx;
   }
 }
+
+/// Collects values that are local to a loop: "loop-local values". A loop-local
+/// value is one that is used exclusively inside the loop but allocated outside
+/// of it. This usually corresponds to temporary values that are used inside the
+/// loop body for initialzing other variables for example.
+///
+/// See `flang/test/Transforms/DoConcurrent/locally_destroyed_temp.f90` for an
+/// example of why we need this.
+///
+/// \param [in] doLoop - the loop within which the function searches for values
+/// used exclusively inside.
+///
+/// \param [out] locals - the list of loop-local values detected for \p doLoop.
+void collectLoopLocalValues(fir::DoLoopOp doLoop,
+                            llvm::SetVector<mlir::Value> &locals) {
+  doLoop.walk([&](mlir::Operation *op) {
+    for (mlir::Value operand : op->getOperands()) {
+      if (locals.contains(operand))
+        continue;
+
+      bool isLocal = true;
+
+      if (!mlir::isa_and_present<fir::AllocaOp>(operand.getDefiningOp()))
+        continue;
+
+      // Values defined inside the loop are not interesting since they do not
+      // need to be localized.
+      if (doLoop->isAncestor(operand.getDefiningOp()))
+        continue;
+
+      for (auto *user : operand.getUsers()) {
+        if (!doLoop->isAncestor(user)) {
+          isLocal = false;
+          break;
+        }
+      }
+
+      if (isLocal)
+        locals.insert(operand);
----------------
skatrak wrote:

Nit: I think something like this might be a bit more concise, but feel free to disagree. In that case, the `isLocal` declaration might be good to move it closer to the loop.
```suggestion
      auto users = operand.getUsers();
      if (llvm::find_if(users, [&](mlir::Operation *user) { return !doLoop->isAncestor(user); }) == users.end())
        locals.insert(operand);
```

https://github.com/llvm/llvm-project/pull/127635