Re: [patch] m68k: Fix binary compatibility problem with -mno-strict-align. (Take 2)

[Nathan Sidwell <nathan at codesourcery dot com>]

Roman Zippel wrote:

> Looking at this a little closer, I'm not sure why this is related to 
> alignment in first place. Whether a structure is returned in a register 
> should be controlled by -fpcc-struct-return/-freg-struct-return and the 
> DEFAULT_PCC_STRUCT_RETURN value in the config. In 
> function.c:aggregate_value_p there is shortly after the return_in_memory 
> hook the following test:
>
>   if (flag_pcc_struct_return && AGGREGATE_TYPE_P (type))
>     return 1;
>
> IMO the alignment should have no influence here, so where is this coming 
> from? 

store layout sets the mode of a structure depending on STRICT_ALIGNMENT.  For 
instance a {short, short} struct will get SI mode if STRICT_ALIGNMENT is false. 
 When it's true such a struct will get BLKmode.  The default can-return-in-reg 
hook examines the type's mode.  If it's BLKmode, it is returned in memory, if 
it's an integral mode it is returned in a register.

nathan
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