1763741 - IntCoordTyped / CoordTyped take too much space on Windows.

Status: RESOLVED FIXED

(Core :: Graphics, defect)

Description

[Emilio Cobos Álvarez (:emilio)]

This patch makes our builds fail on Windows pretty hard:

diff --git a/gfx/2d/Coord.h b/gfx/2d/Coord.h
index fd2ab15f88b5e..07cd88141e5d0 100644
--- a/gfx/2d/Coord.h
+++ b/gfx/2d/Coord.h
@@ -96,8 +96,14 @@ struct IntCoordTyped
 
   using Super = BaseCoord<Rep, IntCoordTyped<units, Rep>>;
 
-  constexpr IntCoordTyped() : Super() {}
-  constexpr MOZ_IMPLICIT IntCoordTyped(Rep aValue) : Super(aValue) {}
+  constexpr IntCoordTyped() : Super() {
+    static_assert(sizeof(IntCoordTyped) == sizeof(Rep),
+                  "Would be unfortunate otherwise!");
+  }
+  constexpr MOZ_IMPLICIT IntCoordTyped(Rep aValue) : Super(aValue) {
+    static_assert(sizeof(IntCoordTyped) == sizeof(Rep),
+                  "Would be unfortunate otherwise!");
+  }
 };
 
 template <class units, class F>
@@ -116,10 +122,19 @@ struct CoordTyped : public BaseCoord<F, CoordTyped<units, F>>,
 
   using Super = BaseCoord<F, CoordTyped<units, F>>;
 
-  constexpr CoordTyped() : Super() {}
-  constexpr MOZ_IMPLICIT CoordTyped(F aValue) : Super(aValue) {}
+  constexpr CoordTyped() : Super() {
+    static_assert(sizeof(CoordTyped) == sizeof(F),
+                  "Would be unfortunate otherwise!");
+  }
+  constexpr MOZ_IMPLICIT CoordTyped(F aValue) : Super(aValue) {
+    static_assert(sizeof(CoordTyped) == sizeof(F),
+                  "Would be unfortunate otherwise!");
+  }
   explicit constexpr CoordTyped(const IntCoordTyped<units>& aCoord)
-      : Super(F(aCoord.value)) {}
+      : Super(F(aCoord.value)) {
+    static_assert(sizeof(CoordTyped) == sizeof(F),
+                  "Would be unfortunate otherwise!");
+  }
 
   void Round() { this->value = floor(this->value + 0.5); }
   void Truncate() { this->value = int32_t(this->value); }

This was caught by Hiro while doing some Rust bindings stuff.

Comment 1

[Emilio Cobos Álvarez (:emilio)]

Attachment: Standalone test-case?

Comment 2

[Emilio Cobos Álvarez (:emilio)]

Attachment: Really standalone test-case.

This program builds on Linux/macOS/Android, but the static assert in main() fails on Windows: https://godbolt.org/z/veaK994j3

Comment 3

[Emilio Cobos Álvarez (:emilio)]

Probably this: https://stackoverflow.com/questions/12701469/why-is-the-empty-base-class-optimization-ebo-is-not-working-in-msvc

Comment 4

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1763741 - Make gfx types take the right amount of space in MSVC. r=jrmuizel!,glandium!

This is an attribute that could be useful elsewhere so seems worth
putting in mfbt.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/235ffcec5f53
Make gfx types take the right amount of space in MSVC. r=jrmuizel,glandium

Comment 6

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/235ffcec5f53