[libcxx] [test] Fix odr_signature tests with optimizations enabled

If optimization is enabled, the inline `f()` function actually gets
inlined, meaning that the functions `tu1()` and `tu2()` trivially
return 1 and 2, instead of actually referencing the potentially
linker deduplicated function `f()`, which is what the test tries
to test.

Mark the inline functions with `__attribute__((noinline))` to make
sure that they don't get inlined even with optimizations enabled.

Also update the TODO comments to explain why we have an XFAIL for
msvc mode here.

This avoids these tests unexpectedly passing if building in
msvc mode, with optimizations enabled
(`-DLIBCXX_TEST_PARAMS="optimization=speed"`).

Author: mstorsjo

libcxx/test/libcxx/odr_signature.exceptions.sh.cpp

@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// TODO: Investigate
+// ABI tags have no effect in MSVC mode.
 // XFAIL: msvc
 
 // Test that we encode whether exceptions are supported in an ABI tag to avoid
@@ -21,14 +21,14 @@
 // -fno-exceptions
 #ifdef TU1
 #  include <__config>
-_LIBCPP_HIDE_FROM_ABI inline int f() { return 1; }
+_LIBCPP_HIDE_FROM_ABI __attribute__((noinline)) inline int f() { return 1; }
 int tu1() { return f(); }
 #endif // TU1
 
 // -fexceptions
 #ifdef TU2
 #  include <__config>
-_LIBCPP_HIDE_FROM_ABI inline int f() { return 2; }
+_LIBCPP_HIDE_FROM_ABI __attribute__((noinline)) inline int f() { return 2; }
 int tu2() { return f(); }
 #endif // TU2
 

libcxx/test/libcxx/odr_signature.hardening.sh.cpp

@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// TODO: Investigate
+// ABI tags have no effect in MSVC mode.
 // XFAIL: msvc
 
 // Test that we encode the hardening mode in an ABI tag to avoid ODR violations
@@ -24,28 +24,28 @@
 // fast hardening mode
 #ifdef TU1
 #  include <__config>
-_LIBCPP_HIDE_FROM_ABI inline int f() { return 1; }
+_LIBCPP_HIDE_FROM_ABI __attribute__((noinline)) inline int f() { return 1; }
 int tu1() { return f(); }
 #endif // TU1
 
 // extensive hardening mode
 #ifdef TU2
 #  include <__config>
-_LIBCPP_HIDE_FROM_ABI inline int f() { return 2; }
+_LIBCPP_HIDE_FROM_ABI __attribute__((noinline)) inline int f() { return 2; }
 int tu2() { return f(); }
 #endif // TU2
 
 // debug hardening mode
 #ifdef TU3
 #  include <__config>
-_LIBCPP_HIDE_FROM_ABI inline int f() { return 3; }
+_LIBCPP_HIDE_FROM_ABI __attribute__((noinline)) inline int f() { return 3; }
 int tu3() { return f(); }
 #endif // TU3
 
 // No hardening
 #ifdef TU4
 #  include <__config>
-_LIBCPP_HIDE_FROM_ABI inline int f() { return 4; }
+_LIBCPP_HIDE_FROM_ABI __attribute__((noinline)) inline int f() { return 4; }
 int tu4() { return f(); }
 #endif // TU4