watchpoint count wrong, think-o

[Andrew Cagney]

Hello,

I think there's a bug in how GDB counts the number of watchpoint 
resources needed:

When first creating a hardware watchpoint, the function:

   static int
   can_use_hardware_watchpoint (struct value *v)

Iterates through the values needed to compute the expression to 
determine how many of those values live in memory and hence how many 
need to be watched.  That total number of watched elements is used when 
determining if there enough watch resources.  E.g., ``a + b'' would be 
two watch elements ``a'' and ``b''. (the value passed down to that Z? 
packet.)

However, when GDB goes a re-count on that same watchpoint (as part of 
computing the watchpoint resources already used), the function:

   hw_watchpoint_used_count (enum bptype type, int *other_type_used)

is used and it does the far simpler computation of just counting up the 
number of watchpoints (and not watchpoint elements).  Hence, ``a + b'' 
gets re-counted as just one watchpoint element.

Anyone agree?  I guess I get to prove this some how :-/

As for fixing it.

- should the number of elements needed be cached in the breakpoint 
structure, or
- re-computed each time

I think a cache is safe since I can't see how the number of elements 
would change.  It would also avoid any overhead in re-calling 
TARGET_REGION_OK_FOR_HW_WATCHPOINT().

Andrew