No extern "C" main functions (#20223)

A user is reporting a build failure with top-of-tree Clang:

https://discourse.llvm.org/t/build-error-of-iree-may-related-to-clang21/85090

> iree/tools/iree-check-module-main.cc:150:16: error: ‘main’ should not
be ‘extern “C”’ [-Werror,-Wmain]

Clang is correct: `main` really can't be `extern "C"`:
https://eel.is/c++draft/basic.start#main-2

> Its type shall have C++ language linkage

Anyway, what was the reason for `extern "C"` ?

---------

Signed-off-by: Benoit Jacob <[email protected]>

Author: bjacob

runtime/src/iree/base/internal/flags.h

@@ -318,7 +318,7 @@ void iree_flags_set_usage(const char* program_name, const char* usage);
 // Returns <0 if parsing fails.
 //
 // Usage:
-//   extern "C" int main(int argc, char** argv) {
+//   int main(int argc, char** argv) {
 //     iree_status_t status = iree_flags_parse(&argc, &argv);
 //     if (!iree_status_is_ok(status)) { exit(1); }
 //     consume_positional_args(argc, argv);

runtime/src/iree/task/executor_demo.cc

@@ -37,7 +37,9 @@ static void simulate_work(const iree_task_tile_context_t* tile_context) {
   }
 }
 
-extern "C" int main(int argc, char* argv[]) {
+}  // namespace
+
+int main(int argc, char* argv[]) {
   IREE_TRACE_APP_ENTER();
   IREE_TRACE_SCOPE_NAMED("ExecutorTest::Any");
 
@@ -168,5 +170,3 @@ extern "C" int main(int argc, char* argv[]) {
   IREE_TRACE_APP_EXIT(0);
   return 0;
 }
-
-}  // namespace

runtime/src/iree/testing/gtest_main.cc

@@ -8,7 +8,7 @@
 #include "iree/base/internal/flags.h"
 #include "iree/testing/gtest.h"
 
-extern "C" int main(int argc, char** argv) {
+int main(int argc, char** argv) {
   IREE_TRACE_APP_ENTER();
 
   // Pass through flags to gtest (allowing --help to fall through).

runtime/src/iree/vm/bytecode/module_size_benchmark.cc

@@ -9,7 +9,7 @@
 #include "iree/vm/bytecode/module.h"
 #include "iree/vm/bytecode/module_size_benchmark_module_c.h"
 
-extern "C" int main(int argc, char** argv) {
+int main(int argc, char** argv) {
   iree_vm_instance_t* instance = nullptr;
   iree_vm_instance_create(IREE_VM_TYPE_CAPACITY_DEFAULT,
                           iree_allocator_system(), &instance);

tools/iree-check-module-main.cc

@@ -147,7 +147,7 @@ iree_status_t Run(iree_allocator_t host_allocator, int* out_exit_code) {
 
 }  // namespace
 
-extern "C" int main(int argc, char** argv) {
+int main(int argc, char** argv) {
   IREE_TRACE_APP_ENTER();
 
   // Pass through flags to gtest (allowing --help to fall through).
@@ -181,3 +181,5 @@ extern "C" int main(int argc, char** argv) {
 }
 
 }  // namespace iree
+
+int main(int argc, char** argv) { return iree::main(argc, argv); }

tools/iree-run-mlir-main.cc

@@ -452,7 +452,7 @@ class ArgParser {
 
 }  // namespace
 
-extern "C" int main(int argc, char** argv) {
+int main(int argc, char** argv) {
   IREE_TRACE_APP_ENTER();
   IREE_TRACE_ZONE_BEGIN_NAMED(z0, "iree-run-mlir");
 
@@ -533,3 +533,5 @@ extern "C" int main(int argc, char** argv) {
 }
 
 }  // namespace iree
+
+int main(int argc, char** argv) { return iree::main(argc, argv); }