From fd0ff033adc55bd2afb8752d24e22a9630d14b7d Mon Sep 17 00:00:00 2001
From: Stephen Heumann <stephenheumann@gmail.com>
Date: Sat, 31 Mar 2018 15:45:05 -0500
Subject: [PATCH] Fix code generation for certain cases where addresses are
 stored to local variables that don't fit in the direct page.

There was a bug when storing addresses generated by expressions like &a[i], where a is a global array and i is a variable. In certain cases where the destination location was a local variable that didn't fit in the direct page, the result of the address calculation would be stored to the wrong location on the stack. This failed to give the correct result, and could also sometimes cause crashes or other problems due to stack corruption.

The following program (derived from a csmith-generated test case) illustrates the issues:

#pragma optimize 1
long g_87[5];
static int g_242 = 4;

int main(void) {
    char l_298[256];
    long *l_284[3] = {0, 0, &g_87[g_242]};
    return l_284[2]-g_87; /* should be 4 */
}
---
 Gen.pas | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/Gen.pas b/Gen.pas
index aeafff2..339818a 100644
--- a/Gen.pas
+++ b/Gen.pas
@@ -3746,19 +3746,25 @@ case optype of
         	  GenImplied(m_tdc);
         	  GenImplied(m_clc);
         	  GenNative(m_adc_imm, immediate, gLong.disp, nil, 0);
-        	  if not gLong.fixedDisp then begin
+                  if not gLong.fixedDisp then
                      GenNative(m_adc_s, direct, 1, nil, 0);
-                     GenImplied(m_ply);
-                     end; {if}
         	  GenNative(m_sta_dirX, direct, 0, nil, 0);
         	  GenNative(m_stz_dirX, direct, 2, nil, 0);
+                  if not gLong.fixedDisp then
+                     GenImplied(m_plx);
         	  end; {else}
 
             globalLabel: begin
                if not gLong.fixedDisp then
-        	  GenImplied(m_txa)
-               else if disp > 253 then
+                  GenImplied(m_txa);
+               if disp > 253 then begin
+                  if op^.opcode = pc_cop then
+                     if not gLong.fixedDisp then
+                        GenImplied(m_tay)
+                     else
+                        GenImplied(m_txy);
         	  GenNative(m_ldx_imm, immediate, disp, nil, 0);
+                  end; {if}
                if gLong.fixedDisp then
         	  GenNative(m_lda_imm, immediate, gLong.disp, gLong.lab, 0)
                else begin
@@ -3774,8 +3780,11 @@ case optype of
         	  GenNative(m_adc_imm, immediate, 0, nil, 0);
                if disp < 254 then
         	  GenNative(m_sta_dir, direct, disp+2, nil, 0)
-               else
+               else begin
         	  GenNative(m_sta_dirX, direct, 2, nil, 0);
+                  if op^.opcode = pc_cop then
+                     GenImplied(m_tyx);
+                  end; {else}
                end;
 
             constant: