[Bug target/26721] [4.2 Regression]: Gcc generates unaligned access

["pinskia at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #14 from pinskia at gcc dot gnu dot org  2006-03-17 00:22 -------
Now ia64-hpux is a different story.
Maybe the real question is why DSE/DCE is not deleting the dead code which it
is?

But for future reference the docs for STRICT_ALIGNMENT is:
@defmac STRICT_ALIGNMENT
Define this macro to be the value 1 if instructions will fail to work
if given data not on the nominal alignment.  If instructions will merely
go slower in that case, define this macro as 0.
@end defmac

Which means by default on ia64-linux-gnu, it should be defined to 1 and then
SLOW_UNALIGNED_ACCESS should return 1.
The docs for that:
@defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment})
Define this macro to be the value 1 if memory accesses described by the
@var{mode} and @var{alignment} parameters have a cost many times greater
than aligned accesses, for example if they are emulated in a trap
handler.

When this macro is nonzero, the compiler will act as if
@code{STRICT_ALIGNMENT} were nonzero when generating code for block
moves.  This can cause significantly more instructions to be produced.
Therefore, do not set this macro nonzero if unaligned accesses only add a
cycle or two to the time for a memory access.

If the value of this macro is always zero, it need not be defined.  If
this macro is defined, it should produce a nonzero value when
@code{STRICT_ALIGNMENT} is nonzero.
@end defmac


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26721