RFA: static cast from base class to derived class

[Jim Blandy <jimb@redhat.com>]

Once when my grandfather was a boy, he was riding his bicycle along a
gravel path, and going pretty fast, when he hit a stone, went flying
over the handlebars, and landed on his face.  The gravel was ground so
deeply into his face that, even in his forties, he'd still
occasionally encounter, while shaving, bits of rock that had finally
worked their way out to the surface.

Here's a patch for a bit of 1998 HP Merge gravel that has finally
found its way to the surface.

I didn't see any regressions with this patch using either STABS or
Dwarf 2.  I'll put together a regression test for the original bug
tomorrow.

2002-08-20  Jim Blandy  <jimb@redhat.com>

	* valops.c (value_cast): Simplify and correct logic for doing a
	static cast from a pointer to a base class to a pointer to a
	derived class.

Index: gdb/valops.c
===================================================================
RCS file: /cvs/src/src/gdb/valops.c,v
retrieving revision 1.67
diff -c -r1.67 valops.c
*** gdb/valops.c	19 Aug 2002 23:19:53 -0000	1.67
--- gdb/valops.c	21 Aug 2002 02:42:21 -0000
***************
*** 361,378 ****
  				       value_zero (t1, not_lval), 0, t1, 1);
  		  if (v)
  		    {
! 		      struct value *v2 = value_ind (arg2);
! 		      VALUE_ADDRESS (v2) -= VALUE_ADDRESS (v)
! 			+ VALUE_OFFSET (v);
! 
!                       /* JYG: adjust the new pointer value and
! 			 embedded offset. */
!                       v2->aligner.contents[0] -=  VALUE_EMBEDDED_OFFSET (v);
!                       VALUE_EMBEDDED_OFFSET (v2) = 0;
! 
! 		      v2 = value_addr (v2);
! 		      VALUE_TYPE (v2) = type;
! 		      return v2;
  		    }
  		}
  	    }
--- 361,371 ----
  				       value_zero (t1, not_lval), 0, t1, 1);
  		  if (v)
  		    {
!                       CORE_ADDR addr2 = value_as_address (arg2);
!                       addr2 -= (VALUE_ADDRESS (v)
!                                 + VALUE_OFFSET (v)
!                                 + VALUE_EMBEDDED_OFFSET (v));
!                       return value_from_pointer (type, addr2);
  		    }
  		}
  	    }