possible structure layout bug

[Stephen Kennedy]

Normally, compilers place members from derived classes starting at
sizeof(base), but gcc breaks this rule if the class contains a simd type
and places the derived member in the padding of the base class.

Reproduced with gcc-3.3 and gcc-3.4 on debian linux x86.
See the attached case

%g++-3.4  layoutbug.cpp && a.out
__m128 size 16, align 16
Quad   size 16, align 16
Base1 32 Derived1 48 Offset 32 <- offset follows sizeof(base)
Base2 32 Derived2 32 Offset 20 <- offset of derived member is inside
Base3 64 Derived3 80 Offset 64 <- sizeof(base class)

Has anybody any comments? I know layouts vary from compiler to compiler,
but this seems to be inconsistent with itself.
Stephen.
-- 
Stephen Kennedy stephen.kennedy@havok.com http://www.havok.com/ 
Game Developer Frontline Award Winner 2002 & 2003
Computer Graphics World 2003 Innovation Award Winner
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