[flang-commits] [flang] [mlir] [MLIR][OpenMP] Support basic materialization for `omp.private` ops (PR #81715)

[Sergio Afonso via flang-commits]

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@@ -1086,12 +1106,98 @@ convertOmpParallel(omp::ParallelOp opInst, llvm::IRBuilderBase &builder,
 
   // TODO: Perform appropriate actions according to the data-sharing
   // attribute (shared, private, firstprivate, ...) of variables.
-  // Currently defaults to shared.
+  // Currently shared and private are supported.
   auto privCB = [&](InsertPointTy allocaIP, InsertPointTy codeGenIP,
                     llvm::Value &, llvm::Value &vPtr,
                     llvm::Value *&replacementValue) -> InsertPointTy {
     replacementValue = &vPtr;
 
+    // If this is a private value, this lambda will return the corresponding
+    // mlir value and its `PrivateClauseOp`. Otherwise, empty values are
+    // returned.
+    auto [privVar, privatizerClone] =
+        [&]() -> std::pair<mlir::Value, omp::PrivateClauseOp> {
+      if (!opInst.getPrivateVars().empty()) {
+        auto privVars = opInst.getPrivateVars();
+        auto privatizers = opInst.getPrivatizers();
+
+        for (auto [privVar, privatizerAttr] :
+             llvm::zip_equal(privVars, *privatizers)) {
+          // Find the MLIR private variable corresponding to the LLVM value
+          // being privatized.
+          llvm::Value *llvmPrivVar = moduleTranslation.lookupValue(privVar);
+          if (llvmPrivVar != &vPtr)
+            continue;
+
+          SymbolRefAttr privSym = llvm::cast<SymbolRefAttr>(privatizerAttr);
+          omp::PrivateClauseOp privatizer =
+              SymbolTable::lookupNearestSymbolFrom<omp::PrivateClauseOp>(
+                  opInst, privSym);
+
+          // Clone the privatizer in case it used by more than one parallel
+          // region. The privatizer is processed in-place (see below) before it
+          // gets inlined in the parallel region and therefore processing the
+          // original op is dangerous.
+          return {privVar, privatizer.clone()};
+        }
+      }
+
+      return {mlir::Value(), omp::PrivateClauseOp()};
+    }();
+
+    if (privVar) {
+      if (privatizerClone.getDataSharingType() ==
+          omp::DataSharingClauseType::FirstPrivate) {
+        privatizerClone.emitOpError(
+            "TODO: delayed privatization is not "
+            "supported for `firstprivate` clauses yet.");
+        bodyGenStatus = failure();
+        return codeGenIP;
+      }
+
+      Region &allocRegion = privatizerClone.getAllocRegion();
+
+      if (!allocRegion.hasOneBlock()) {
+        privatizerClone.emitOpError(
+            "TODO: multi-block alloc regions are not supported yet. Seems "
----------------
skatrak wrote:

Nit: Feel free to ignore if you disagree, but in my opinion this is a bit too implementation-specific information for users. I'd just leave "multi-block alloc regions are not supported yet" as the error message and add the rest as a comment in the code.

https://github.com/llvm/llvm-project/pull/81715