[mlir] Add a function to print C-strings to RunnerUtils.cpp.

[pifon2a]

update

[pifon2a]

Add an awesome test.

mlir/lib/ExecutionEngine/RunnerUtils.cpp

extern "C" void print_memref_f32(int64_t rank, void *ptr) {
   _mlir_ciface_print_memref_f32(&descriptor);
 }
 
 extern "C" void print_memref_f64(int64_t rank, void *ptr) {
   UnrankedMemRefType<double> descriptor = {rank, ptr};
   _mlir_ciface_print_memref_f64(&descriptor);
 }
 
+extern "C" void print_c_string(char *str) { printf("%s", str); }
+
 extern "C" void
 _mlir_ciface_print_memref_0d_f32(StridedMemRefType<float, 0> *M) {
   impl::printMemRef(*M);
 }
 extern "C" void
 _mlir_ciface_print_memref_1d_f32(StridedMemRefType<float, 1> *M) {
   impl::printMemRef(*M);
 }

mlir/test/mlir-cpu-runner/print.mlir

+// RUN: mlir-opt %s -pass-pipeline="convert-func-to-llvm,reconcile-unrealized-casts" \
+// RUN: | mlir-cpu-runner -e main -entry-point-result=void \
+// RUN:   -shared-libs=%mlir_runner_utils_dir/libmlir_runner_utils%shlibext,%mlir_runner_utils_dir/libmlir_c_runner_utils%shlibext \
+// RUN: | FileCheck %s
+
+
+llvm.mlir.global internal constant @str_global("String to print\0A")
+llvm.func @print_c_string(!llvm.ptr<i8>)
+
+func @main() {
+  %0 = llvm.mlir.addressof @str_global : !llvm.ptr<array<16 x i8>>
+  %1 = llvm.mlir.constant(0 : index) : i64
+  %2 = llvm.getelementptr %0[%1, %1]
+    : (!llvm.ptr<array<16 x i8>>, i64, i64) -> !llvm.ptr<i8>
+  llvm.call @print_c_string(%2) : (!llvm.ptr<i8>) -> ()
+  return
+}
+
+// CHECK: String to print