[llvm-branch-commits] [flang] [Flang][OMP] Replace SUM intrinsic call with SUM operations (PR #113082)

[Tom Eccles via llvm-branch-commits]

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@@ -335,49 +336,129 @@ static void parallelizeRegion(Region &sourceRegion, Region &targetRegion,
     for (auto [i, opOrSingle] : llvm::enumerate(regions)) {
       bool isLast = i + 1 == regions.size();
       if (std::holds_alternative<SingleRegion>(opOrSingle)) {
-        OpBuilder singleBuilder(sourceRegion.getContext());
-        Block *singleBlock = new Block();
-        singleBuilder.setInsertionPointToStart(singleBlock);
-
         OpBuilder allocaBuilder(sourceRegion.getContext());
         Block *allocaBlock = new Block();
         allocaBuilder.setInsertionPointToStart(allocaBlock);
 
-        OpBuilder parallelBuilder(sourceRegion.getContext());
-        Block *parallelBlock = new Block();
-        parallelBuilder.setInsertionPointToStart(parallelBlock);
-
-        auto [allParallelized, copyprivateVars] =
-            moveToSingle(std::get<SingleRegion>(opOrSingle), allocaBuilder,
-                         singleBuilder, parallelBuilder);
-        if (allParallelized) {
-          // The single region was not required as all operations were safe to
-          // parallelize
-          assert(copyprivateVars.empty());
-          assert(allocaBlock->empty());
-          delete singleBlock;
+        it = block.begin();
+        while (&*it != terminator)
+          if (isa<hlfir::SumOp>(it))
+            break;
+          else
+            it++;
+
+        if (auto sumOp = dyn_cast<hlfir::SumOp>(it)) {
+          /// Implementation:
+          /// Intrinsic function `SUM` operations
+          /// --
+          /// x = sum(array)
+          ///
+          /// is converted to
+          ///
+          /// !$omp parallel do
+          /// do i = 1, size(array)
+          ///     x = x + array(i)
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tblah wrote:

I don't think this will work. `x` will be simultaneously updated from all of the threads - overwriting each-other. It is a classic race condition.

I think you need to add a reduction clause to the wsloop operation reducing `x` with `+`.

https://github.com/llvm/llvm-project/pull/113082