From 60b472a99ee295cdd4ba304a6485f09bf16fea13 Mon Sep 17 00:00:00 2001
From: Stephen Heumann <stephenheumann@gmail.com>
Date: Mon, 4 Mar 2024 19:37:52 -0600
Subject: [PATCH] Optimize generated code for some indexing ops in large memory
 model.

This generates slightly better code for indexing a global/static char array with a signed 16-bit index and a positive offset, e.g. a[i+1].

Here is an example that is affected:

#pragma memorymodel 1
#pragma optimize -1
char a[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
int main(int argc, char *argv[]) {
        return a[argc+2];
}
---
 Gen.pas | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/Gen.pas b/Gen.pas
index b27d586..0121b25 100644
--- a/Gen.pas
+++ b/Gen.pas
@@ -3617,11 +3617,17 @@ else begin
    else begin
       if op^.left^.opcode = pc_lao then begin
          GenTree(op^.right);
-         if signed then
-            GenImplied(m_tay);
+         GenNative(m_ldx_imm, immediate, op^.left^.q, op^.left^.lab, shift16);
+         if signed then begin
+            GenImpliedForFlags(m_tay);
+            lab2 := GenLabel;
+            GenNative(m_bpl, relative, lab2, nil, 0);
+            GenImplied(m_dex);
+            GenLab(lab2);
+            signed := false;
+            end; {if}
          GenImplied(m_clc);
          GenNative(m_adc_imm, immediate, op^.left^.q, op^.left^.lab, 0);
-         GenNative(m_ldx_imm, immediate, op^.left^.q, op^.left^.lab, shift16);
          end {if}
       else begin
          gLong.preference := onStack;