[sdcc-devel] [ sdcc-Feature Requests-1494382 ] sdcc optimization

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Feature Requests item #1494382, was opened at 2006-05-24 08:21
Message generated for change (Tracker Item Submitted) made by Item Submitter
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Category: None
Group: None
Status: Open
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: sdcc optimization

Initial Comment:
SDCC regularily reinserts the same value into registers
- most noteably, the xdata dptr registers:

Is it possible to keep currentl values for each
register to determine whether there is a need to set
the register or leave it alone?

eg:

{
  xdata lock;

  if (--lock)
     mybit = 0;
}

-------
                            986 ;     genMinus
   0073 90 07 F0            987         mov     dptr,#_lock
                            988 ;     genMinusDec
   0076 E0                  989         movx    a,@dptr
   0077 14                  990         dec     a
                            991 ;     genAssign
   0078 90 07 F0            992         mov     dptr,#_lock
   007B F0                  993         movx    @dptr,a
                            994 ;     genAssign
   007C 90 07 F0            995         mov     dptr,#_lock
   007F E0                  996         movx    a,@dptr
                            997 ;     genIfx
                            998 ;       Peephole 105  
 removed redundant mov
   0080 FD                  999         mov     r5,a
                           1000 ;     genIfxJump
                           1001 ;       Peephole 109  
 removed ljmp by inverse jump logic
   0081 70 02              1002         jnz     00102$
   0083                    1003 00127$:
                           1004 ;     genAssign
   0083 D2 CD              1005         setb    _mybit
----


There are a number of other places where sdcc could do
much better as well:

 moving data into registers which are then not used. etc.

Is it possible to extend the peephole syntax to allow
specifying that n unrelated instructions can occur
between the sequence in question?

ie say to optimize:

   push   ar2
   push   ar3
   mov    r5, a
   pop    ar3
   pop    ar2

say:  (a better syntax could be found I'm sure)
replace restart {
        pop %1
        x = *(mov, add, dec) ! %1
        push %1
    } by {
        ; nop  - peepfile
        x
    }

where the wildcard format is:

      <x> = [*](inst1, inst2, !inst3, [*]) ! %[arg1],
%[arg2], ... %[argn]

match sequence <x> where:
   [*] - any of: (if no star .. must be all of)
    (inst1, ..) instruction list.
       !instx  - exclude instruction (eg lcall)
       * - match any instruction.
         - if followed by a !inst4, then remove inst4
from list of all instructions.

    ! %[arg1], %[arg2]  - where arg1, arg2, ... was
unreferenced


--
Carl van Schaik

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