[llvm-branch-commits] [flang] [mlir] [mlir][OpenMP] Pack task private variables into a heap-allocated context struct (PR #125307)

[Sergio Afonso via llvm-branch-commits]

================
@@ -1794,37 +1909,118 @@ convertOmpTaskOp(omp::TaskOp taskOp, llvm::IRBuilderBase &builder,
       moduleTranslation, allocaIP);
 
   // Allocate and initialize private variables
-  // TODO: package private variables up in a structure
   builder.SetInsertPoint(initBlock->getTerminator());
-  for (auto [privDecl, mlirPrivVar, blockArg] :
-       llvm::zip_equal(privateDecls, mlirPrivateVars, privateBlockArgs)) {
-    llvm::Type *llvmAllocType =
-        moduleTranslation.convertType(privDecl.getType());
 
-    // Allocations:
-    builder.SetInsertPoint(allocaIP.getBlock()->getTerminator());
-    llvm::Value *llvmPrivateVar = builder.CreateAlloca(
-        llvmAllocType, /*ArraySize=*/nullptr, "omp.private.alloc");
+  // Create task variable structure
+  taskStructMgr.generateTaskContextStruct();
+  // GEPs so that we can initialize the variables. Don't use these GEPs inside
+  // of the body otherwise it will be the GEP not the struct which is fowarded
+  // to the outlined function. GEPs forwarded in this way are passed in a
+  // stack-allocated (by OpenMPIRBuilder) structure which is not safe for tasks
+  // which may not be executed until after the current stack frame goes out of
+  // scope.
+  taskStructMgr.createGEPsToPrivateVars();
+
+  for (auto [privDecl, mlirPrivVar, blockArg, llvmPrivateVarAlloc] :
+       llvm::zip_equal(privateDecls, mlirPrivateVars, privateBlockArgs,
+                       taskStructMgr.getLLVMPrivateVarGEPs())) {
+    if (!privDecl.readsFromMold())
+      // to be handled inside the task
+      continue;
+    assert(llvmPrivateVarAlloc &&
+           "reads from mold so shouldn't have been skipped");
 
-    auto err =
+    llvm::Expected<llvm::Value *> privateVarOrErr =
         initPrivateVar(builder, moduleTranslation, privDecl, mlirPrivVar,
-                       blockArg, llvmPrivateVar, llvmPrivateVars, initBlock);
-    if (err)
+                       blockArg, llvmPrivateVarAlloc, initBlock);
+    if (auto err = privateVarOrErr.takeError())
----------------
skatrak wrote:

Same comment as above, I'm not sure if this handling can cause issues. I'd suggest:
```c++
if (!privateVarOrErr)
  return handleError(privateVarOrErr.takeError(), *taskOp.getOperation());
```

https://github.com/llvm/llvm-project/pull/125307