Support tests in freestanding

Summary:
Freestanding is *weird*. The standard allows it to differ in a bunch of odd
manners from regular C++, and the committee would like to improve that
situation. I'd like to make libc++ behave better with what freestanding should
be, so that it can be a tool we use in improving the standard. To do that we
need to try stuff out, both with "freestanding the language mode" and
"freestanding the library subset".

Let's start with the super basic: run the libc++ tests in freestanding, using
clang as the compiler, and see what works. The easiest hack to do this:

In utils/libcxx/test/config.py add:

  self.cxx.compile_flags += ['-ffreestanding']

Run the tests and they all fail.

Why? Because in freestanding `main` isn't special. This "not special" property
has two effects: main doesn't get mangled, and main isn't allowed to omit its
`return` statement. The first means main gets mangled and the linker can't
create a valid executable for us to test. The second means we spew out warnings
(ew) and the compiler doesn't insert the `return` we omitted, and main just
falls of the end and does whatever undefined behavior (if you're luck, ud2
leading to non-zero return code).

Let's start my work with the basics. This patch changes all libc++ tests to
declare `main` as `int main(int, char**` so it mangles consistently (enabling us
to declare another `extern "C"` main for freestanding which calls the mangled
one), and adds `return 0;` to all places where it was missing. This touches 6124
files, and I apologize.

The former was done with The Magic Of Sed.

The later was done with a (not quite correct but decent) clang tool:

  https://gist.github.com/jfbastien/793819ff360baa845483dde81170feed

This works for most tests, though I did have to adjust a few places when e.g.
the test runs with `-x c`, macros are used for main (such as for the filesystem
tests), etc.

Once this is in we can create a freestanding bot which will prevent further
regressions. After that, we can start the real work of supporting C++
freestanding fairly well in libc++.

<rdar://problem/47754795>

Reviewers: ldionne, mclow.lists, EricWF

Subscribers: christof, jkorous, dexonsmith, arphaman, miyuki, libcxx-commits

Differential Revision: https://reviews.llvm.org/D57624

llvm-svn: 353086

6 files changed, 18 insertions, 6 deletions

diff --git a/libcxx/test/std/language.support/cmp/cmp.common/common_comparison_category.pass.cpp b/libcxx/test/std/language.support/cmp/cmp.common/common_comparison_category.pass.cpp
index 4c999637ffb..218291b6b49 100644
--- a/libcxx/test/std/language.support/cmp/cmp.common/common_comparison_category.pass.cpp
+++ b/libcxx/test/std/language.support/cmp/cmp.common/common_comparison_category.pass.cpp
@@ -33,7 +33,7 @@ void test_cat() {
 
 // [class.spaceship]p4: The 'common comparison type' U of a possibly-empty list
 //   of 'n' types T0, T1, ..., TN, is defined as follows:
-int main() {
+int main(int, char**) {
   using WE = std::weak_equality;
   using SE = std::strong_equality;
   using PO = std::partial_ordering;
@@ -89,4 +89,6 @@ int main() {
     test_cat<SO, SO>();
     test_cat<SO, SO, SO>();
   }
+
+  return 0;
 }
diff --git a/libcxx/test/std/language.support/cmp/cmp.partialord/partialord.pass.cpp b/libcxx/test/std/language.support/cmp/cmp.partialord/partialord.pass.cpp
index 6c51b7a208d..f2e673db696 100644
--- a/libcxx/test/std/language.support/cmp/cmp.partialord/partialord.pass.cpp
+++ b/libcxx/test/std/language.support/cmp/cmp.partialord/partialord.pass.cpp
@@ -155,9 +155,11 @@ constexpr bool test_constexpr() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test_static_members();
   test_signatures();
   static_assert(test_conversion(), "conversion test failed");
   static_assert(test_constexpr(), "constexpr test failed");
+
+  return 0;
 }
diff --git a/libcxx/test/std/language.support/cmp/cmp.strongeq/cmp.strongeq.pass.cpp b/libcxx/test/std/language.support/cmp/cmp.strongeq/cmp.strongeq.pass.cpp
index e34cadc55ce..a5af910a5e0 100644
--- a/libcxx/test/std/language.support/cmp/cmp.strongeq/cmp.strongeq.pass.cpp
+++ b/libcxx/test/std/language.support/cmp/cmp.strongeq/cmp.strongeq.pass.cpp
@@ -87,9 +87,11 @@ constexpr bool test_constexpr() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test_static_members();
   test_signatures();
   test_conversion();
   static_assert(test_constexpr(), "constexpr test failed");
+
+  return 0;
 }
diff --git a/libcxx/test/std/language.support/cmp/cmp.strongord/strongord.pass.cpp b/libcxx/test/std/language.support/cmp/cmp.strongord/strongord.pass.cpp
index 4b75e5d51ef..a31fd34d4f1 100644
--- a/libcxx/test/std/language.support/cmp/cmp.strongord/strongord.pass.cpp
+++ b/libcxx/test/std/language.support/cmp/cmp.strongord/strongord.pass.cpp
@@ -203,9 +203,11 @@ constexpr bool test_constexpr() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test_static_members();
   test_signatures();
   static_assert(test_conversion(), "conversion test failed");
   static_assert(test_constexpr(), "constexpr test failed");
+
+  return 0;
 }
diff --git a/libcxx/test/std/language.support/cmp/cmp.weakeq/cmp.weakeq.pass.cpp b/libcxx/test/std/language.support/cmp/cmp.weakeq/cmp.weakeq.pass.cpp
index dae2f214717..367aac6bebe 100644
--- a/libcxx/test/std/language.support/cmp/cmp.weakeq/cmp.weakeq.pass.cpp
+++ b/libcxx/test/std/language.support/cmp/cmp.weakeq/cmp.weakeq.pass.cpp
@@ -62,8 +62,10 @@ constexpr bool test_constexpr() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test_static_members();
   test_signatures();
   static_assert(test_constexpr(), "constexpr test failed");
+
+  return 0;
 }
diff --git a/libcxx/test/std/language.support/cmp/cmp.weakord/weakord.pass.cpp b/libcxx/test/std/language.support/cmp/cmp.weakord/weakord.pass.cpp
index 6e9e7d44106..ada8d240b6d 100644
--- a/libcxx/test/std/language.support/cmp/cmp.weakord/weakord.pass.cpp
+++ b/libcxx/test/std/language.support/cmp/cmp.weakord/weakord.pass.cpp
@@ -160,9 +160,11 @@ constexpr bool test_constexpr() {
   return true;
 }
 
-int main() {
+int main(int, char**) {
   test_static_members();
   test_signatures();
   static_assert(test_conversion(), "conversion test failed");
   static_assert(test_constexpr(), "constexpr test failed");
+
+  return 0;
 }