Prevent LTCG (MSVC LTO) from removing "pck" section

[Listwon]

Fixes #35590

MSVC doesn't have equivalent of GCC __attribute__((used)) so this is the easiest workaround I could think of to prevent removing unused section.

[RandomShaper]

For a bit more safety it may be worthy to surround the assignment with
#pragma optimize( "", off )
and
#pragma optimize( "", on )
.

[Listwon]

According to the documentation this won't work

The optimize pragma must appear outside a function. It takes effect at the first function defined after the pragma is seen. The on and off arguments turn options specified in the optimization-list on or off.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.5.

[akien-mga]

Cherry-picked for 3.4.3.

[akien-mga]

This seems to have broken template build with MinGW-GCC at least:

platform/windows/godot_windows.cpp: In function 'int widechar_main(int, wchar_t**)':
platform/windows/godot_windows.cpp:145:22: error: invalid conversion from 'const char*' to 'char*' [-fpermissive]
  145 |  char *dummy_guard = dummy;
      |                      ^~~~~
      |                      |
      |                      const char*

This can either be fixed with:

diff --git a/platform/windows/godot_windows.cpp b/platform/windows/godot_windows.cpp
index c4926209c7..506c903c35 100644
--- a/platform/windows/godot_windows.cpp
+++ b/platform/windows/godot_windows.cpp
@@ -41,7 +41,7 @@
 #pragma section("pck", read)
 __declspec(allocate("pck")) static char dummy[8] = { 0 };
 #elif defined __GNUC__
-static const char dummy[8] __attribute__((section("pck"), used)) = { 0 };
+static char dummy[8] __attribute__((section("pck"), used)) = { 0 };
 #endif
 #endif

or:

diff --git a/platform/windows/godot_windows.cpp b/platform/windows/godot_windows.cpp
index c4926209c7..906403c592 100644
--- a/platform/windows/godot_windows.cpp
+++ b/platform/windows/godot_windows.cpp
@@ -142,7 +142,7 @@ int widechar_main(int argc, wchar_t **argv) {
 
 #ifndef TOOLS_ENABLED
 	// Workaround to prevent LTCG (MSVC LTO) from removing "pck" section
-	char *dummy_guard = dummy;
+	char *dummy_guard = (char *)dummy;
 #endif
 
 	char **argv_utf8 = new char *[argc];

Not sure which is best / preserves the compiler magic that keeps this section in place.

[Listwon]

Hmm, I think that it would be better to just wrap this part in #if defined _MSC_VER as this is MSVC-only workaround. Sorry I didn't think about it earlier (I missed the difference between const char* for GCC and char * for MSVC).