Normalized C++ compilation options for single-threaded targets

src/Compilation.zig

@@ -1180,6 +1180,15 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
         if (must_single_thread and !single_threaded) {
             return error.TargetRequiresSingleThreaded;
         }
+        if (!single_threaded and options.link_libcpp) {
+            if (options.target.cpu.arch.isARM()) {
+                log.warn(
+                    \\libc++ does not work on multi-threaded ARM yet.
+                    \\For more details: https://github.com/ziglang/zig/issues/6573
+                , .{});
+                return error.TargetRequiresSingleThreaded;
+            }
+        }
 
         const llvm_cpu_features: ?[*:0]const u8 = if (build_options.have_llvm and use_llvm) blk: {
             var buf = std.ArrayList(u8).init(arena);
@@ -3803,6 +3812,10 @@ pub fn addCCArgs(
         try argv.append("-D_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS");
         try argv.append("-D_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS");
         try argv.append("-D_LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS");
+
+        if (comp.bin_file.options.single_threaded) {
+            try argv.append("-D_LIBCPP_HAS_NO_THREADS");
+        }
     }
 
     if (comp.bin_file.options.link_libunwind) {

src/libcxx.zig

@@ -128,6 +128,12 @@ pub fn buildLibCXX(comp: *Compilation) !void {
             continue;
         if (std.mem.startsWith(u8, cxx_src, "src/support/ibm/") and target.os.tag != .zos)
             continue;
+        if (comp.bin_file.options.single_threaded) {
+            if (std.mem.startsWith(u8, cxx_src, "src/support/win32/thread_win32.cpp")) {
+                continue;
+            }
+            try cflags.append("-D_LIBCPP_HAS_NO_THREADS");
+        }
 
         try cflags.append("-DNDEBUG");
         try cflags.append("-D_LIBCPP_BUILDING_LIBRARY");
@@ -145,8 +151,7 @@ pub fn buildLibCXX(comp: *Compilation) !void {
         }
 
         if (target.os.tag == .wasi) {
-            // WASI doesn't support thread and exception yet.
-            try cflags.append("-D_LIBCPP_HAS_NO_THREADS");
+            // WASI doesn't support exceptions yet.
             try cflags.append("-fno-exceptions");
         }
 
@@ -264,13 +269,20 @@ pub fn buildLibCXXABI(comp: *Compilation) !void {
         var cflags = std.ArrayList([]const u8).init(arena);
 
         if (target.os.tag == .wasi) {
-            // WASI doesn't support thread and exception yet.
-            if (std.mem.startsWith(u8, cxxabi_src, "src/cxa_thread_atexit.cpp") or
-                std.mem.startsWith(u8, cxxabi_src, "src/cxa_exception.cpp") or
+            // WASI doesn't support exceptions yet.
+            if (std.mem.startsWith(u8, cxxabi_src, "src/cxa_exception.cpp") or
                 std.mem.startsWith(u8, cxxabi_src, "src/cxa_personality.cpp"))
                 continue;
-            try cflags.append("-D_LIBCXXABI_HAS_NO_THREADS");
             try cflags.append("-fno-exceptions");
+        }
+
+        // WASM targets are single threaded.
+        if (comp.bin_file.options.single_threaded) {
+            if (std.mem.startsWith(u8, cxxabi_src, "src/cxa_thread_atexit.cpp")) {
+                continue;
+            }
+            try cflags.append("-D_LIBCXXABI_HAS_NO_THREADS");
+            try cflags.append("-D_LIBCPP_HAS_NO_THREADS");
         } else {
             try cflags.append("-DHAVE___CXA_THREAD_ATEXIT_IMPL");
         }

test/standalone/c_compiler/build.zig

@@ -29,7 +29,7 @@ pub fn build(b: *Builder) void {
     exe_cpp.addCSourceFile("test.cpp", &[0][]const u8{});
     exe_cpp.setBuildMode(mode);
     exe_cpp.setTarget(target);
-    exe_cpp.linkSystemLibrary("c++");
+    exe_cpp.linkLibCpp();
 
     switch (target.getOsTag()) {
         .windows => {

test/standalone/c_compiler/test.c

@@ -1,25 +1,28 @@
 #include <assert.h>
 #include <stdio.h>
+#include <stdlib.h>
 
-typedef struct  {
-    int val;
+typedef struct {
+  int val;
 } STest;
 
 int getVal(STest* data) { return data->val; }
 
 int main (int argc, char *argv[])
 {
-	STest* data = (STest*)malloc(sizeof(STest));
-    data->val = 123;
+  STest* data = (STest*)malloc(sizeof(STest));
+  data->val = 123;
 
-    assert(getVal(data) != 456);
-    int ok = (getVal(data) == 123);
+  assert(getVal(data) != 456);
+  int ok = (getVal(data) == 123);
 
-    if (argc>1) fprintf(stdout, "val=%d\n", data->val);
+  if (argc > 1) {
+    fprintf(stdout, "val=%d\n", data->val);
+  }
 
-    free(data);
+  free(data);
 
-    if (!ok) abort();
+  if (!ok) abort();
 
-	return 0;
+  return EXIT_SUCCESS;
 }

test/standalone/c_compiler/test.cpp

@@ -1,33 +1,79 @@
-#include <iostream>
 #include <cassert>
+#include <iostream>
+
+#ifndef _LIBCPP_HAS_NO_THREADS
+#include <future>
+#endif
+
+thread_local unsigned int tls_counter = 1;
+
+// a non-optimized way of checking for prime numbers:
+bool is_prime(int x) {
+  for (int i = 2; i <x ; ++i) {
+    if (x % i == 0) {
+      return false;
+    }
+  }
+  return true;
+}
 
 class CTest {
 public:
-	CTest(int val) : m_val(val) {};
-	virtual ~CTest() {}
+  CTest(int val) : m_val(val) {
+    tls_counter++;
+  };
+  virtual ~CTest() {}
 
-	virtual int getVal() const { return m_val; }
-	virtual void printVal() { std::cout << "val=" << m_val << std::endl; }
+  virtual int getVal() const { return m_val; }
+  virtual void printVal() { std::cout << "val=" << m_val << std::endl; }
 private:
-	int m_val;
+  int m_val;
+};
+
+class GlobalConstructorTest {
+public:
+  GlobalConstructorTest(int val) : m_val(val) {};
+  virtual ~GlobalConstructorTest() {}
+
+  virtual int getVal() const { return m_val; }
+  virtual void printVal() { std::cout << "val=" << m_val << std::endl; }
+private:
+  int m_val;
 };
 
 
 volatile int runtime_val = 456;
-CTest global(runtime_val);	// test if global initializers are called.
+GlobalConstructorTest global(runtime_val);	// test if global initializers are called.
 
 int main (int argc, char *argv[])
 {
-	assert(global.getVal() == 456);
+  assert(global.getVal() == 456);
+
+  auto t = std::make_unique<CTest>(123);
+  assert(t->getVal() != 456);
+  assert(tls_counter == 2);
+  if (argc > 1) {
+    t->printVal();
+  }
+  bool ok = t->getVal() == 123;
 
-	auto* t = new CTest(123);
-	assert(t->getVal()!=456);
+  if (!ok) abort();
 
-	if (argc>1) t->printVal();
-	bool ok = t->getVal() == 123;
-	delete t;
+#ifndef _LIBCPP_HAS_NO_THREADS
+  std::future<bool> fut = std::async(is_prime, 313);
+  bool ret = fut.get();
+  assert(ret);
+#endif
 
-	if (!ok) abort();
+#if !defined(__wasm__) && !defined(__APPLE__)
+  // WASM and macOS are not passing this yet.
+  // TODO file an issue for this and link it here.
+  try {
+    throw 20;
+  } catch (int e) {
+    assert(e == 20);
+  }
+#endif
 
-	return 0;
+  return EXIT_SUCCESS;
 }