Re: alpha haifa regression

[Joern Rennecke <amylaar at cygnus dot co dot uk>]

>   In message <199709292200.PAA08832@cygnus.com>you write:
[Richard Henderson:]
>   > 	But since the tests in true_dependance are symmetric, that will
>   > 	then cause problems for va_arg(list, int), no?
>   > 
[Jim Wilson:]
>   > I would suspect no, because va_arg(list, int) expands into complicated code
>   > that does an actual aggregate (array and/or structure) memory access, and
>   > hence va_arg references are always aggregate references, even if a scalar
>   > type is specified.
> I suspect yes -- I've already seen it on the PA.

I just checked it for alpha. pa and sh.  For a TYPE argument, va_arg
basically casts (or assigns) a void* to a TYPE*, and then dereferences
the TYPE*.  The result is a memory access that has MEM_IN_STRUCT_P set
iff TYPE is a struct.

I propose to cast to a (struct { TYPE t;} *) instead, and dereference that
and select the t member (can of course both be done with the -> operator).

If TYPE is smaller than STRUCTURE_SIZE_BOUNDARY, and the target is
big endian, we have to adjust the alignment padding.
care.  We have then to 
the t member of this structure.  

>   > It is easy enough to check by looking at the RTL generated by a va_arg
>   > call using a scalar.  I suspect that it will have MEM_IN_STRUCT_P set.
> Depends on the target, but most end up doing something like this if
> you remove all the casts, address computations & rounding:
> 
> 
>   blah = *(type*)address

It is actually has an impact what form address takes.  If it happens to be
a a (type *) might happen for type == char if some port uses char *
for address) and the actual operation is a cast with a following dereference,
without an intervening assignment to a variable, the actual form of address
matters - i.e. if there is some non-zero integer added to a pointer, the
MEM_IN_STRUCT_P of the resulting mem gets set.

However, what I have seen so far either uses an ntervening assignment,
or an intervening cast to (void*), thus resulting in a MEM without
MEM_IN_STRUCT_P.