Disable a peephole optimization that can produce bad code.

The optimization applies to code sequences like:
	dec abs
	lda abs
	beq ...
where the dec and lda were supposed to refer to the same location.

There were two problems with this optimization as written:
-It considered the dec and lda to refer to the same location even if they were actually references to different elements of the same array.
-It did not work in the case where the A register value was needed in subsequent code.

The first of these was already an issue in previous ORCA/C releases, as in the following example:

#pragma optimize -1
int x[2] = {0,0};
int main(void) {
        --x[0];
        if (x[1] != 0)
                return 123;
        return 0; /* should return 0 */
}

I do not believe the second problem was triggered by any code sequences generated in previous releases of ORCA/C, but it can be triggered after commit 4c402fc88, e.g. by the following example:

#pragma optimize -1
int x = 1;
int main(void) {
        int y = 123;
        --x;
        return x == 0; /* should return 1 */
}

Since the circumstances where this peephole optimization was triggered validly are pretty obscure, just disabling it should have a minimal impact on the generated code.

Native.pas

@@ -1720,11 +1720,12 @@ var
                                     Remove(ns+3);
                                     end; {if}
 
-         m_dec_abs:
+         {disabled - can generate bad code}
+         {m_dec_abs:
             if npeep[ns+1].opcode = m_lda_abs then
                if name^ = npeep[ns+1].name^ then
                   if npeep[ns+2].opcode = m_beq then
-                     Remove(ns+1);
+                     Remove(ns+1);}
 
          m_lda_abs:
             if npeep[ns+1].opcode = m_clc then begin
@@ -2657,7 +2658,7 @@ yRegister.condition := regUnknown;
 lastRegOpcode := 0; {BRK}
 nnextspot := 1;
 nleadOpcodes := [m_asl_a,m_bcc,m_bcs,m_beq,m_bmi,m_bne,m_bpl,m_brl,{m_bvs,}
-   m_dec_abs,m_lda_abs,m_lda_dir,m_lda_imm,m_ldx_imm,m_sta_abs,m_sta_dir,
+   {m_dec_abs,}m_lda_abs,m_lda_dir,m_lda_imm,m_ldx_imm,m_sta_abs,m_sta_dir,
    m_pha,m_plb,{m_plx,}m_tax,m_tya,m_tyx,m_phy,m_pei_dir,m_ldy_imm,m_rep,
    m_ora_dir,m_ora_abs,m_and_imm,m_pea,m_tcd];
 nstopOpcodes := [d_end,d_pin];

cc.notes

@@ -1618,6 +1618,8 @@ If you use #pragma debug 0x0010 to enable stack check debug code, the compiler w
 
 14. If a struct, union, or enum type name appeared within the third expression in a for loop statement (e.g. in a cast or as the argument to sizeof), ORCA/C could behave incorrectly.  It could report a spurious error if a semicolon occurred within the type name as part of a structure or union member declaration.  Also, any tags or enumeration constants declared by such a type name should be in scope within the loop body, but they were not.
 
+15. Native code peephole optimization might produce invalid code in some obscure circumstances where one element of a global or static array was decremented and then another element of the same array was accessed immediately thereafter.
+
 -- Bugs from C 2.1.1 B3 that have been fixed in C 2.2.0 ---------------------
 
 1.  There were various bugs that could cause incorrect code to be generated in certain cases.  Some of these were specific to certain optimization passes, alone or in combination.