From 393b7304a05f12358ad072f5409a437bfd377836 Mon Sep 17 00:00:00 2001
From: Stephen Heumann <stephenheumann@gmail.com>
Date: Wed, 6 Jul 2022 22:24:54 -0500
Subject: [PATCH] Optimize 16-bit multiplication by various constants.

This optimizes most multiplications by a power of 2 or the sum of two powers of 2, converting them to equivalent operations using shifts which should be faster than the general-purpose multiplication routine.
---
 CGI.pas    |   1 +
 Gen.pas    | 128 ++++++++++++++++++++++++++++++++++++++++++++---------
 Native.pas |   2 +-
 3 files changed, 110 insertions(+), 21 deletions(-)

diff --git a/CGI.pas b/CGI.pas
index 5f560f1..a03be6e 100644
--- a/CGI.pas
+++ b/CGI.pas
@@ -147,6 +147,7 @@ const
    m_ply                  =    122;
    m_plp                  =     40;
    m_rep                  =    194;
+   m_ror_a                =    $6A;
    m_rtl                  =    107;
    m_rts                  =     96;
    m_sbc_abs              =    237;
diff --git a/Gen.pas b/Gen.pas
index 2aed6d0..176b44d 100644
--- a/Gen.pas
+++ b/Gen.pas
@@ -6441,29 +6441,117 @@ procedure GenTree {op: icptr};
    
    var
       nd: icptr;
+      val: integer;
 
    begin {GenMpi}
-   if not Complex(op^.left) then
+   if ((op^.left^.opcode = pc_ldc) or (op^.right^.opcode = pc_ldc))
+      and ((op^.opcode = pc_umi) or (not rangeCheck)) then begin
+      if op^.left^.opcode = pc_ldc then begin
+         val := op^.left^.q;
+         nd := op^.right;
+         end {if}
+      else begin
+         val := op^.right^.q;
+         nd := op^.left;
+         end; {else}
+      if nd^.opcode = pc_ldc then
+         GenNative(m_lda_imm, immediate, long(ord4(val) * nd^.q).lsw, nil, 0)
+      else begin
+         GenTree(nd);
+         case val of
+            0: GenNative(m_lda_imm, immediate, 0, nil, 0);
+
+            1,2,4,8,16,32,64,128:
+               while not odd(val) do begin  
+                  GenImplied(m_asl_a);
+                  val := val >> 1;
+                  end; {while}
+
+            256,512,1024,2048,4096,8192,16384: begin
+               GenNative(m_and_imm, immediate, $00FF, nil, 0);
+               GenImplied(m_xba);
+               val := val >> 8;
+               while not odd(val) do begin  
+                  GenImplied(m_asl_a);
+                  val := val >> 1;
+                  end; {while}
+               end;
+
+            3,5,6,9,10,12,17,18,20,24,33,34,36,40,48,65,66,68,72,80,96: begin
+               if odd(val) then         {prevent lda+pha -> pei optimization}
+                  GenLab(GenLabel);
+               while not odd(val) do begin  
+                  GenImplied(m_asl_a);
+                  val := val >> 1;
+                  end; {while}
+               GenImplied(m_pha);
+               val := val - 1;
+               while not odd(val) do begin  
+                  GenImplied(m_asl_a);
+                  val := val >> 1;
+                  end; {while}
+               GenImplied(m_clc);
+               GenNative(m_adc_s, direct, 1, nil, 0);
+               GenImplied(m_plx);
+               end;
+
+            -1,-2,-4,-8,-16,-32,-64,-128: begin
+               GenNative(m_eor_imm, immediate, -1, nil, 0);
+               GenImplied(m_ina);
+               val := -val;
+               while not odd(val) do begin  
+                  GenImplied(m_asl_a);
+                  val := val >> 1;
+                  end; {while}
+               end;
+
+            -256: begin
+               GenNative(m_eor_imm, immediate, -1, nil, 0);
+               GenImplied(m_ina);
+               GenNative(m_and_imm, immediate, $00FF, nil, 0);
+               GenImplied(m_xba);
+               end;
+
+            otherwise: begin
+               if val = $8000 then begin
+                  GenImplied(m_lsr_a);
+                  GenNative(m_lda_imm, immediate, 0, nil, 0);
+                  GenImplied(m_ror_a);
+                  end {if}
+               else begin
+                  GenNative(m_ldx_imm, immediate, val, nil, 0);
+                  if op^.opcode = pc_mpi then
+                     GenCall(28)
+                  else {pc_umi}
+                     GenCall(94);
+                  end; {else}
+               end;
+            end; {case}
+         end; {else}
+      end {if}
+   else begin
+      if not Complex(op^.left) then
+         if Complex(op^.right) then begin
+            nd := op^.left;
+            op^.left := op^.right;
+            op^.right := nd;
+            end; {if}
+      GenTree(op^.left);
       if Complex(op^.right) then begin
-	 nd := op^.left;
-	 op^.left := op^.right;
-	 op^.right := nd;
-	 end; {if}
-   GenTree(op^.left);
-   if Complex(op^.right) then begin
-      GenImplied(m_pha);
-      GenTree(op^.right);
-      GenImplied(m_plx);
-      end {if}
-   else
-      LoadX(op^.right);
-   if op^.opcode = pc_mpi then begin
-      GenCall(28);      
-      if rangeCheck then
-         GenCall(25);
-      end {if}
-   else {pc_umi}
-      GenCall(94);
+         GenImplied(m_pha);
+         GenTree(op^.right);
+         GenImplied(m_plx);
+         end {if}
+      else
+         LoadX(op^.right);
+      if op^.opcode = pc_mpi then begin
+         GenCall(28);      
+         if rangeCheck then
+            GenCall(25);
+         end {if}
+      else {pc_umi}
+         GenCall(94);
+      end; {else}
    end; {GenMpi}
 
 
diff --git a/Native.pas b/Native.pas
index 1de7f29..173c566 100644
--- a/Native.pas
+++ b/Native.pas
@@ -775,7 +775,7 @@ case p_opcode of
    m_ora_dir,m_ora_dirX,m_ora_imm,m_ora_long,m_ora_longX,m_ora_s,m_pla,
    m_sbc_abs,m_sbc_dir,m_sbc_imm,m_sbc_s,m_tdc,m_tsc,m_adc_indl,m_adc_indly,
    m_and_indl,m_and_indly,m_ora_indl,m_ora_indly,m_sbc_indl,m_sbc_indly,
-   m_eor_indl,m_eor_indly:
+   m_eor_indl,m_eor_indly,m_ror_a:
       aRegister.condition := regUnknown;
 
    m_ldy_absX,m_ldy_dirX,m_ply: