[RFA] Tweak in skip_prologue for rs6000

["Michael Snyder" <michsnyd@cisco.com>]

Kevin, 

If I'm right, this will prevent saving lr_offset twice.  It looks like the 
existing code intends to invalidate lr_reg, but setting it to zero is not
an invalid value.

Probably the same is true for cr_reg and cr_offset...

Michael

2004-11-10  msnyder  <msnyder@redhat.com>

 * rs6000-tdep.c (skip_prologue): After saving lr_offset, 
 must invalidate lr_reg (so we don't try to save it again).  

Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.230
diff -p -r1.230 rs6000-tdep.c
*** rs6000-tdep.c 13 Oct 2004 16:38:22 -0000 1.230
--- rs6000-tdep.c 11 Nov 2004 01:04:40 -0000
*************** skip_prologue (CORE_ADDR pc, CORE_ADDR l
*** 981,987 ****
     continue;
  
   }
!       else if (lr_reg != -1 &&
          /* std Rx, NUM(r1) || stdu Rx, NUM(r1) */
          (((op & 0xffff0000) == (lr_reg | 0xf8010000)) ||
    /* stw Rx, NUM(r1) */
--- 981,987 ----
     continue;
  
   }
!       else if (lr_reg >= 0 &&
          /* std Rx, NUM(r1) || stdu Rx, NUM(r1) */
          (((op & 0xffff0000) == (lr_reg | 0xf8010000)) ||
    /* stw Rx, NUM(r1) */
*************** skip_prologue (CORE_ADDR pc, CORE_ADDR l
*** 991,997 ****
   { /* where Rx == lr */
     fdata->lr_offset = offset;
     fdata->nosavedpc = 0;
!    lr_reg = 0;
     if ((op & 0xfc000003) == 0xf8000000 || /* std */
         (op & 0xfc000000) == 0x90000000)  /* stw */
       {
--- 991,999 ----
   { /* where Rx == lr */
     fdata->lr_offset = offset;
     fdata->nosavedpc = 0;
!    /* Invalidate lr_reg, but don't set it to -1.
!       That would mean that it had never been set.  */
!    lr_reg = -2;
     if ((op & 0xfc000003) == 0xf8000000 || /* std */
         (op & 0xfc000000) == 0x90000000)  /* stw */
       {