strict aliasing violations.
Post-merge fix: include my_compiler.h before my_attribute.h
as the latter will undef __attribute__ if the compiler is not
GCC. Based on the compiler version, in my_compiler.h we know
for sure whether the aligned attribute is supported. Furthermore,
undefining attribute might cause bugs if some system header
uses it.
include/my_compiler.h:
Drop aligned attribute support from Sun Studio C++ compiler
as its not clear exactly which version of it supports the
attribute.
strict aliasing violations.
Another rather noisy violation of strict aliasing rules
is the spatial code which makes use of stack-based memory
(of type Geometry_buffer) to provide placement for Geometry
objects. Although a placement new is allowed to dynamically
change the type of a object, the object returned by the
new placement was being ignored and the original stack-based
object was being casted to the new type, thus violating strict
aliasing rules.
The solution is to reorganize the code so that the object
returned by the new placement is used instead of casting the
original object. Also, to ensure that the stack-based object
is properly aligned with respect to the objects it provides
placement for, a set of compiler-dependent macros and types
are introduced so that the alignment of objects can be inquired
and specified.
include/Makefile.am:
Add new header.
include/my_compiler.h:
Add new header.
include/my_global.h:
Remove now-unnecessary macros.
sql/spatial.cc:
Make object creation functions return the object whose type
was dynamically changed by the new placement.
Move static method from the header in order to avoid having
to access a forward declaration.
sql/spatial.h:
Object creation callbacks now take a array of chars as the
storage area.
Move create_by_typeid to a source file as to not access the
forward declaration of Geometry_buffer.
Ensure that Geometry_buffer is properly aligned.
sql/sql_show.cc:
Use newly added aligned storage helper.
