Better heuristics for symbols

[larsbrinkhoff]

Improve how the symbol table is used for disassembly.

[larsbrinkhoff]

Examples:

• jfcl u, 112541 - The JFCL AC field is usually a number.
• consz cfhpo9, @usrpdl(q) - Prefer device codes for IO instructions.
• addi a, l - Maybe in some cases prefer numbers for immediate operands?
• xctri b, 105657 - Prefer X symbols for XCTR and XCTRI.
• skipn tabp, shutdn - When the AC is optional and is 0, leave the field blank rather than use a symbol which is 0.

[larsbrinkhoff]

In the AC field, the symbols A-E, P, T, TT could receive some special treatment. Maybe more. This is just a heuristic, but the vast majority of ITS programs use these AC definitions.

[larsbrinkhoff]

More examples:

• .logout unfn1, - If AC is 0, disassemble as .logout.
• .value unfn1 - If argument is 0, don't print it.

[larsbrinkhoff]

CC @atsampson, maybe you have some ideas around this?

[atsampson]

I was thinking about this again recently...

Symbols with a value of 0-17 that are neither killed nor halfkilled are probably AC names. When symbolising instruction fields, have some hints about which fields are/aren't likely to be ACs - e.g. SETZM 1(A) is more likely than SETZM A(1) or SETZM A(A), and MOVEI A,1 is more likely than MOVEI A,A.

And as you suggested above, if I have A==1 and FOOBIT==1, then the symboliser should prefer A. Maybe just preferring shorter symbol names would work for this.

For STINK programs with multiple sections of symbols, it'd be nice to have a way of ignoring some sections (e.g. the AGC symbols in Muddle, which are only valid when the GC is mapped in).

[larsbrinkhoff]

Useful hints:

• Opcode field. Possibly match LUUOs?
• Device code from IOT instructions.
• Accumulator or index field. I don't think it's useful to have those separate.
• Accumulator field as number. E.g. JRST and .LOGOUT.
• Accumulator field from XCTR.
• Address field as memory reference.
• Address field as immediate.
• Accumulator = 0 is not printed: SKIP etc.
• Address = 0 is not printed: .VALUE etc.

Some of these combine in interesting ways.

[larsbrinkhoff]

Maybe a hint that the address is often a literal, to be disassembled in line?

[larsbrinkhoff]

Accumulator or address 0 is already implemented as PDP10_A_UNUSED and PDP10_E_UNUSED.