[flang-commits] [flang] [mlir] [flang][OpenMP] Enable delayed privatizaiton by defualt `omp.wsloop` (PR #122471)

[Sergio Afonso via flang-commits]

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@@ -1874,6 +1874,60 @@ convertOmpWsloop(Operation &opInst, llvm::IRBuilderBase &builder,
   llvm::OpenMPIRBuilder::InsertPointTy allocaIP =
       findAllocaInsertPoint(builder, moduleTranslation);
 
+  // The following loop is workaround until we private ops' alloca regions to be
+  // "pure". See
+  // https://discourse.llvm.org/t/rfc-openmp-supporting-delayed-task-execution-with-firstprivate-variables/83084/7
+  // and https://discourse.llvm.org/t/delayed-privatization-for-omp-wsloop/83989
+  // for more info.
+  for (auto [privateVar, privateDeclOp] :
+       llvm::zip_equal(mlirPrivateVars, privateDecls)) {
+    llvm::Value *llvmValue = moduleTranslation.lookupValue(privateVar);
+    bool isAllocArgUsed =
+        !privateDeclOp.getAllocRegion().args_begin()->use_empty();
+
+    // If the alloc region argument is not used, we can skip the workaround.
+    if (!isAllocArgUsed)
+      continue;
+
+    llvm::Instruction *definingInst =
+        llvm::dyn_cast<llvm::Instruction>(llvmValue);
+
+    // If the alloc region argument is not defined by an op, it has to dominate
+    // the current alloc IP. So we skip the workaround.
+    if (!definingInst)
+      continue;
+
+    llvm::Function *definingFun = definingInst->getParent()->getParent();
+    llvm::Function *allocaFun = allocaIP.getBlock()->getParent();
+
+    // If the alloc region argument is defined in a different function that
+    // current one where allocs are being inserted (for example, we are building
+    // the outlined function of a target region), we skip the workaround.
+    if (definingFun != allocaFun)
+      continue;
+
+    llvm::DominatorTree dt(*definingFun);
+    // If the defining instruction of the alloc region argument dominates the
+    // alloca insertion point already, we can skip the workaround.
+    if (dt.dominates(definingInst, allocaIP.getPoint()))
+      continue;
+
+    llvm::BasicBlock *definingBlock = definingInst->getParent();
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skatrak wrote:

Nit: Since it's also part of the initialization of `definingFun`, this can be moved up and reused.

https://github.com/llvm/llvm-project/pull/122471