From 60efb4d882db5539077cf4bea30f88de7ac99c40 Mon Sep 17 00:00:00 2001
From: Stephen Heumann <stephenheumann@gmail.com>
Date: Mon, 18 Jul 2022 21:18:26 -0500
Subject: [PATCH] Generate better code for indexed jumps.

They now use a jmp (addr,X) instruction, rather than a more complicated code sequence using rts. This is an improvement that was suggested in an old Genie message from Todd Whitesel.
---
 CGI.pas    |  2 ++
 Gen.pas    |  6 ++----
 Native.pas | 16 +++++++++-------
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/CGI.pas b/CGI.pas
index e049280..e040852 100644
--- a/CGI.pas
+++ b/CGI.pas
@@ -45,6 +45,7 @@ const
    constantOpnd           =     64;     {the absolute operand is a constant}
    localLab               =    128;     {the operand is a local lab}
    forFlags               =    256;     {instruction used for effect on flags only}
+   subtract1              =    512;     {subtract 1 from address operand}
 
    m_adc_abs              =    $6D;     {op code #s for 65816 instructions}
    m_adc_dir              =    $65;
@@ -103,6 +104,7 @@ const
    m_inx                  =    232;
    m_iny                  =    200;
    m_jml                  =     92;
+   m_jmp_indX             =    $7C;
    m_jsl                  =     34;
    m_lda_abs              =    173;
    m_lda_absx             =    189;
diff --git a/Gen.pas b/Gen.pas
index 28e76a4..708db71 100644
--- a/Gen.pas
+++ b/Gen.pas
@@ -5535,7 +5535,7 @@ procedure GenTree {op: icptr};
    GenNative(m_lda_imm, genAddress, lab1, nil, shift16);
    GenNative(m_sta_s, direct, 6, nil, 0);
    GenNative(m_rep, immediate, 32, nil, 0);
-   GenNative(m_lda_imm, genAddress, lab1, nil, 0);
+   GenNative(m_lda_imm, genAddress, lab1, nil, subtract1);
    GenNative(m_sta_s, direct, 4, nil, 0);
 
    {indirect call}
@@ -7316,9 +7316,7 @@ procedure GenTree {op: icptr};
    GenImplied(m_asl_a);
    GenImplied(m_tax);
    lab1 := GenLabel;
-   GenNative(m_lda_longx, longAbs, lab1, nil, 0);
-   GenImplied(m_pha);
-   GenImplied(m_rts);
+   GenNative(m_jmp_indX, absolute, lab1, nil, 0);
    GenLab(lab1);
    end; {GenXjp}
 
diff --git a/Native.pas b/Native.pas
index e48e711..4d1272e 100644
--- a/Native.pas
+++ b/Native.pas
@@ -731,8 +731,10 @@ case mode of
             LabelSearch(operand, 2, 16, 0)
          else
             LabelSearch(operand, 1, 16, 0)
+      else if (flags & subtract1) <> 0 then
+         LabelSearch(operand, 0, 0, 0)
       else
-         LabelSearch(operand, 0, 0, 0);
+         LabelSearch(operand, 2, 0, 0);
       end;
 
    special:
@@ -819,7 +821,7 @@ case p_opcode of
       goto 3;
    
    m_bra,m_brl,m_clc,m_cmp_abs,m_cmp_dir,m_cmp_imm,m_cmp_s,m_cmp_indl,
-   m_cmp_indly,m_cpx_imm,m_jml,m_plb,m_rtl,m_rts,m_sec,d_add,d_pin,
+   m_cmp_indly,m_cpx_imm,m_jml,m_jmp_indX,m_plb,m_rtl,m_rts,m_sec,d_add,d_pin,
    m_cpx_abs,m_cpx_dir,m_cmp_dirx,m_plp,m_cop,d_wrd:    ;
 
    m_pea: begin
@@ -1523,11 +1525,11 @@ var
       for i := ns to nnextSpot-1 do begin
          opcode := npeep[i].opcode;
          if opcode in
-            [m_bcc,m_bcs,m_beq,m_bmi,m_bne,m_bpl,m_bra,m_brl,m_bvs,m_jml,m_jsl,
-             m_lda_abs,m_lda_absx,m_lda_dir,m_lda_dirx,m_lda_imm,m_lda_indl,
-             m_lda_indly,m_lda_long,m_lda_longx,m_lda_s,m_mvn,m_pla,m_rtl,
-             m_rts,m_tdc,m_txa,m_tya,m_tsc,d_end,d_bmov,d_add,d_pin,d_wrd,
-             d_sym,d_cns] then begin
+            [m_bcc,m_bcs,m_beq,m_bmi,m_bne,m_bpl,m_bra,m_brl,m_bvs,m_jml,
+             m_jmp_indX,m_jsl,m_lda_abs,m_lda_absx,m_lda_dir,m_lda_dirx,
+             m_lda_imm,m_lda_indl,m_lda_indly,m_lda_long,m_lda_longx,m_lda_s,
+             m_mvn,m_pla,m_rtl,m_rts,m_tdc,m_txa,m_tya,m_tsc,d_end,d_bmov,
+             d_add,d_pin,d_wrd,d_sym,d_cns] then begin
             ASafe := true;
             goto 1;
             end {if}