[OpenMP][MLIR] Add a conversion pattern for the master op

[kiranchandramohan]

Summary

The conversion pattern is particularly useful for conversion of
block arguments in the master op.

mlir/lib/Conversion/OpenMPToLLVM/OpenMPToLLVM.cpp

matchAndRewrite(OpType curOp, ArrayRef<Value> operands,
     rewriter.eraseOp(curOp);
     return success();
   }
 };
 } // namespace
 
 void mlir::populateOpenMPToLLVMConversionPatterns(LLVMTypeConverter &converter,
                                                   RewritePatternSet &patterns) {
-  patterns.add<RegionOpConversion<omp::ParallelOp>,
+  patterns.add<RegionOpConversion<omp::MasterOp>,
+               RegionOpConversion<omp::ParallelOp>,
                RegionOpConversion<omp::WsLoopOp>>(converter);
 }
 
 namespace {
 struct ConvertOpenMPToLLVMPass
     : public ConvertOpenMPToLLVMBase<ConvertOpenMPToLLVMPass> {
   void runOnOperation() override;
 };
 } // namespace
 
 void ConvertOpenMPToLLVMPass::runOnOperation() {
   auto module = getOperation();
 
   // Convert to OpenMP operations with LLVM IR dialect
   RewritePatternSet patterns(&getContext());
   LLVMTypeConverter converter(&getContext());
   populateMemRefToLLVMConversionPatterns(converter, patterns);
   populateStdToLLVMConversionPatterns(converter, patterns);
   populateOpenMPToLLVMConversionPatterns(converter, patterns);
 
   LLVMConversionTarget target(getContext());
-  target.addDynamicallyLegalOp<omp::ParallelOp, omp::WsLoopOp>(
+  target.addDynamicallyLegalOp<omp::MasterOp, omp::ParallelOp, omp::WsLoopOp>(
       [&](Operation *op) { return converter.isLegal(&op->getRegion(0)); });
   target.addLegalOp<omp::TerminatorOp, omp::TaskyieldOp, omp::FlushOp,
                     omp::BarrierOp, omp::TaskwaitOp>();
   if (failed(applyPartialConversion(module, target, std::move(patterns))))
     signalPassFailure();
 }
 
 std::unique_ptr<OperationPass<ModuleOp>> mlir::createConvertOpenMPToLLVMPass() {
   return std::make_unique<ConvertOpenMPToLLVMPass>();
 }

mlir/test/Conversion/OpenMPToLLVM/convert-to-llvmir.mlir

 // RUN: mlir-opt -convert-openmp-to-llvm %s  -split-input-file | FileCheck %s
 
+// CHECK-LABEL: llvm.func @master_block_arg
+func @master_block_arg() {
+  // CHECK: omp.master
+  omp.master {
+  // CHECK-NEXT: ^[[BB0:.*]](%[[ARG1:.*]]: i64, %[[ARG2:.*]]: i64):
+  ^bb0(%arg1: index, %arg2: index):
+    // CHECK-NEXT: "test.payload"(%[[ARG1]], %[[ARG2]]) : (i64, i64) -> ()
+    "test.payload"(%arg1, %arg2) : (index, index) -> ()
+    omp.terminator
+  }
+  return
+}
+
 // CHECK-LABEL: llvm.func @branch_loop
 func @branch_loop() {
   %start = constant 0 : index
   %end = constant 0 : index
   // CHECK: omp.parallel
   omp.parallel {
     // CHECK-NEXT: llvm.br ^[[BB1:.*]](%{{[0-9]+}}, %{{[0-9]+}} : i64, i64
     br ^bb1(%start, %end : index, index)