[fw/sdcc] / src / pic / peeph.def

// PIC Port Peep rules
//
//
// INTRODUCTION:
//
// The peep hole optimizer searchs the
// the SDCC generated code for small snippets
// that can be optimized. As a user, you have
// control over this optimization process without
// having to learn the SDCC source code. (However
// you'll still need access to the source since
// these rules are compiled into the source.)
//
// The way it works is you specify the target
// snippet that you want replaced with a more 
// efficient snippet that you write. Wild card
// variables allow the rules to be parameterized.
// 
// In all of the SDCC ports, labels and operands
// can be wild cards. However, in the PIC even the
// instructions can be wild cards.
//
// EXAMPLE:
//
// Consider Peep Rule 1 as an example. This rule
// replaces some code like:
//
//   skpz           ;i.e. btfss status,Z
//    goto    lab1
//   clrw
//lab1:
//
// with:
//
//   skpnz     ;i.e. btfsc status,Z
//    clrw
//lab1
//
// However, the Rule has wild cards four wild cards.
// The first allows the btfss instruction operate
// on anything, not just the Z bit in status register.
// The second wild card applies to a label.
// The third wild card is for an instruction - any
// single instruction can be substituted.
// The fourth wild card is also an instruction. It's
// just an instruction place holder associated with
// a label (think of it as the PIC Port author's laziness
// imposed upon the user).
//
//
// CONDITIONS
//
// There are certain instances where a peep rule may not
// be applicable. Consider this subtle example:
//
//     movwf    R0
//     movf     R0,W
//
// It would seem that the second move is unnecessary. But
// be careful! The movf instruction affects the 'Z' bit.
// So if this sequence is followed by a btfsc status,Z, you
// will have to leave the second move in.
//
// To get around this proble, the peep rule can be followed
// by a conditon:  "if NZ". Which is to say, apply the rule
// if Z bit is not needed in the code that follows. The optimizer
// is smart enough to look more than one instruction past the
// target block...
//
//


replace restart {
        btfss   %1
        goto    %2
        %3
%2:     %4
} by {
        ;peep 1 - test/jump to test/skip
        btfsc   %1
        %3
%2:     %4
}

replace restart {
        btfsc   %1
        goto    %2
        %3
%2:     %4
} by {
        ;peep 1a - test/jump to test/skip
        btfss   %1
        %3
%2:     %4
}

replace restart {
        btfss   %1
        goto    %4
%2:     %3
%4:     %5
} by {
        ;peep 1b - test/jump to test/skip
        btfsc   %1
%2:     %3
%4:     %5
}

replace restart {
        btfsc   %1
        goto    %4
%2:     %3
%4:     %5
} by {
        ;peep 1c - test/jump to test/skip
        btfss   %1
%2:     %3
%4:     %5
}


//bogus test for pcode
//replace restart {
//      movf    %1,w    ;comment at end
//%4:   movf    %1,w
//      RETURN
//      clrf    INDF
//      movlw   0xa5
//      movf    fsr,w
//      incf    indf,f
//      %2
//} by {
//      ; peep test remove redundant move
//%4:   movf    %1,w    ;another comment
//      %2
//} if AYBABTU %3


// peep 2
replace restart {
        movwf   %1
        movf    %1,w
} by {
        ; peep 2 - Removed redundant move
        movwf   %1
} if NZ

// peep 3
replace restart {
        decf    %1,f
        movf    %1,w
        btfss   status,z
        goto    %2
} by {
        ; peep 3 - decf/mov/skpz to decfsz
        decfsz  %1,f
         goto   %2
}


replace restart {
        movf    %1,w
        movf    %1,w
} by {
        ; peep 8 - Removed redundant move
        movf    %1,w
}


replace restart {
        movlw   %1
        movwf   %2
        movlw   %1
} by {
        ; peep 10 - Removed redundant move
        movlw   %1
        movwf   %2
}

replace restart {
        movwf   %1
        movwf   %1
} by {
        ; peep 11 - Removed redundant move
        movwf   %1
}