[llvm-dev] TI 59 backend

[Bruce Hoult via llvm-dev]

Certainly a calculator supports arithmetic :-)

The TI 58/59 support things such as 1 3 STO IND 02 which, if memory 02
currently holds "42", will store 13 into memory 42.

So, yes, there are pointers. And address arithmetic.

On Wed, Mar 14, 2018 at 11:30 AM, Friedman, Eli via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On 3/14/2018 8:53 AM, via llvm-dev wrote:
>
>> Hello,
>>
>> I am a new comer to llvm framework. I read quite many tutorials but I am
>> still not able to determine whether llvm can be used for my project:
>> implementing a backend for the famous Texas Instruments 59 Calculator (sold
>> from 1977 to 1982).
>>
>> This is not a CPU but it uses a kind of bytecode that is interpreted (see
>> examples in http://ti59compiler.wixsite.com/ti59/t-compiler). It has no
>> stack, no frame, only floating point registers. The memory is split between
>> program (up to 960 steps) and registers (up to 100). A register consumes 8
>> program steps, reducing the program size accordingly.
>>
>> The most tricky part is the following: a simple instruction like MOV R1,N
>> may require more or less bytes to be coded. For instance:
>>
>>     MOV R1,1   will require 3 bytes: (key) 1, STO, 01.
>>     MOV R2,345 will require 5 bytes: (key) 3, (key) 4, (key) 5, STO, 02.
>>
>> How to cope with such an instruction? Can llvm be used to generate the
>> right bytecode?
>>
>
> From your description, it sounds like the architecture doesn't support
> pointers or integer arithmetic; that probably makes it impossible to write
> a usable LLVM backend.
>
> Instruction sets with with multiple instruction sizes are relatively
> common; x86, Thumb2, microMIPS, and RISCV all fall into this category.
>
> -Eli
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
> Foundation Collaborative Project
>
>
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