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

[Pranav Bhandarkar via llvm-branch-commits]

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@@ -1794,38 +1909,114 @@ 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.getLLVMPrivateVars())) {
+    if (!privDecl.readsFromMold())
+      // to be handled inside the task
+      continue;
+    assert(llvmPrivateVarAlloc &&
+           "reads from mold so shouldn't have been skipped");
 
-    // builder.SetInsertPoint(initBlock->getTerminator());
-    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())
       return handleError(std::move(err), *taskOp.getOperation());
+
+    llvm::IRBuilderBase::InsertPointGuard guard(builder);
+    builder.SetInsertPoint(builder.GetInsertBlock()->getTerminator());
+
+    // TODO: this is a bit of a hack for Fortran character boxes
----------------
bhandarkar-pranav wrote:

Could you please elaborate on the problem/special handling here in the comments?

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