Re: 8-byte register values on a 32-bit machine

[Keith Walker <keith dot walker at arm dot com>]

At 11:25 03/03/2003 +0000, Richard Earnshaw wrote:
> > On Sat, Mar 01, 2003 at 06:42:58PM -0500, Andrew Cagney wrote:
> >
> > By the way, assuming I can find the time (ugh) I'm not done with
> > LOC_COMPUTED yet.  On my list so far:
> >   - Location lists
> >   - Turning locations into better defined objects
> >   - Thus, allowing LOC_COMPUTED to return a non-computed "location"
> >   - Allowing more complex locations, namely DW_OP_piece style.
> >   - Eventually turning on more uses of DW_OP_piece in GCC.
>
> The main reason gcc allocates objects to contiguous register ranges is
> because gdb can't handle anything else.  Fixing gdb to allow location
> lists would be a major step forward, since then gcc would be able to split
> double-register objects before register allocation and allocate each part
> individually.  That could be a major win on register starved machines.

Actually it is the implementation of the DW_OP_piece operator (rather than 
location lists) which allows the location of an object to be split into 
multiple sub-locations.

Location lists allows, for any given PC value, for you to describe zero 
(optimized out) or more locations for an object.     These locations can 
then be broken down into sub-locations if the resulting expression 
evaluated then contains a DW_OP_piece operator.

Keith