[mlir] support translating OpenMP loops with reductions

Use the recently introduced OpenMPIRBuilder facility to transate OpenMP
workshare loops with reductions to LLVM IR calling OpenMP runtime. Most of the
heavy lifting is done at the OpenMPIRBuilder. When other OpenMP dialect
constructs grow support for reductions, the translation can be updated to
operate on, e.g., an operation interface for all reduction containers instead
of workshare loops specifically. Designing such a generic translation for the
single operation that currently supports reductions is premature since we don't
know how the reduction modeling itself will be generalized.

Reviewed By: kiranchandramohan

Differential Revision: https://reviews.llvm.org/D107343

Author: ftynse

mlir/include/mlir/Target/LLVMIR/ModuleTranslation.h

@@ -83,6 +83,9 @@ class ModuleTranslation {
     return valueMapping.lookup(value);
   }
 
+  /// Looks up remapped a list of remapped values.
+  SmallVector<llvm::Value *> lookupValues(ValueRange values);
+
   /// Stores the mapping between an MLIR block and LLVM IR basic block.
   void mapBlock(Block *mlir, llvm::BasicBlock *llvm) {
     auto result = blockMapping.try_emplace(mlir, llvm);
@@ -110,6 +113,10 @@ class ModuleTranslation {
     return branchMapping.lookup(op);
   }
 
+  /// Removes the mapping for blocks contained in the region and values defined
+  /// in these blocks.
+  void forgetMapping(Region &region);
+
   /// Returns the LLVM metadata corresponding to a reference to an mlir LLVM
   /// dialect access group operation.
   llvm::MDNode *getAccessGroup(Operation &opInst,
@@ -134,9 +141,6 @@ class ModuleTranslation {
   /// Converts the type from MLIR LLVM dialect to LLVM.
   llvm::Type *convertType(Type type);
 
-  /// Looks up remapped a list of remapped values.
-  SmallVector<llvm::Value *, 8> lookupValues(ValueRange values);
-
   /// Returns the MLIR context of the module being translated.
   MLIRContext &getContext() { return *mlirModule->getContext(); }
 
@@ -209,7 +213,7 @@ class ModuleTranslation {
   /// translated makes the frame available when translating ops within that
   /// region.
   template <typename T, typename... Args>
-  void stackPush(Args &&... args) {
+  void stackPush(Args &&...args) {
     static_assert(
         std::is_base_of<StackFrame, T>::value,
         "can only push instances of StackFrame on ModuleTranslation stack");

mlir/lib/Target/LLVMIR/CMakeLists.txt

@@ -27,8 +27,6 @@ add_mlir_translation_library(MLIRTargetLLVMIRExport
 
   LINK_LIBS PUBLIC
   MLIRLLVMIR
-  MLIROpenACC
-  MLIROpenMP
   MLIRLLVMIRTransforms
   MLIRTranslation
   )