[Mlir-commits] [mlir] [mlir] Translating task_reduction clause for pass-by-value vars to LLVMIR (PR #125218)

[Jack Styles]

================
@@ -2469,6 +2473,240 @@ convertOmpTaskOp(omp::TaskOp taskOp, llvm::IRBuilderBase &builder,
   return success();
 }
 
+/*
+ * Utility function for translating `red_init`, `red_comb`, and `red_fini` to
+ * LLVMIR. The ulitity first (commonly) generates a skeleton for any of the
+ * three functions, and then generates the function body based on the
+ * specific operations involved in `red_init` (codegen related to initialization
+ * of task reduction variables) and `red_comb` (codegen related to combination).
+ * Currently, codegen for `red_fini` is skipped since finalization is optional
+ * for `task_reduction` clause, but this ulitity has the capability of defining
+ * finalization if needed. Finally, the returned `llvm::Function` is used to
+ * populate the relevant entries in the task reduction specific data structure.
+ */
+static llvm::Value *createTaskReductionFunction(
+    omp::TaskgroupOp &op, llvm::IRBuilderBase &builder, const std::string &name,
+    llvm::Type *redTy, LLVM::ModuleTranslation &moduleTranslation,
+    omp::DeclareReductionOp &reductionDecl, Region &region, unsigned cnt,
+    SmallVectorImpl<llvm::Value *> &privateReductionVariables,
+    DenseMap<Value, llvm::Value *> &reductionVariableMap) {
+
+  llvm::LLVMContext &Context = builder.getContext();
+  // TODO: by-ref reduction variables are yet to be handled.
+  llvm::DataLayout DL = builder.GetInsertBlock()->getModule()->getDataLayout();
+  llvm::Type *OpaquePtrTy =
+      llvm::PointerType::get(Context, DL.getProgramAddressSpace());
+  if (region.empty() && name == "red_fini")
+    // Finalization is optional for reductions.
+    return llvm::Constant::getNullValue(OpaquePtrTy);
+
+  // Prepare a general structure of the function to be emitted
+  llvm::FunctionType *funcType =
+      llvm::FunctionType::get(OpaquePtrTy, {OpaquePtrTy, OpaquePtrTy}, false);
+  llvm::Function *function =
+      llvm::Function::Create(funcType, llvm::Function::ExternalLinkage, name,
+                             builder.GetInsertBlock()->getModule());
+  function->setDoesNotRecurse();
+  llvm::BasicBlock *entry =
+      llvm::BasicBlock::Create(Context, "entry", function);
+  llvm::IRBuilder<> bbBuilder(entry);
+
+  // Prepare the function arguments
+  llvm::Value *arg0 = function->getArg(0);
+  llvm::Value *arg1 = function->getArg(1);
+
+  if (name == "red_init") {
+    // For the initialization, map the reduction variables
+    // to the arguments of the function
+    function->addParamAttr(0, llvm::Attribute::NoAlias);
+    function->addParamAttr(1, llvm::Attribute::NoAlias);
+    Region &initializerRegion = reductionDecl.getInitializerRegion();
+    Block &entry = initializerRegion.front();
+
+    mlir::Value mlirSource = op.getTaskReductionVars()[cnt];
+    llvm::Value *llvmSource = moduleTranslation.lookupValue(mlirSource);
+    llvm::Value *origVal = llvmSource;
+
+    moduleTranslation.mapValue(reductionDecl.getInitializerMoldArg(), origVal);
+
+    if (entry.getNumArguments() > 1) {
+      llvm::Value *allocation =
----------------
Stylie777 wrote:

```suggestion
      llvm::Value *allocation = reductionVariableMap.lookup(mlirSource);
```
We can reuse the value for mlirSource from above.

https://github.com/llvm/llvm-project/pull/125218