[llvm-dev] [MSP430] Plans for MSP430 improvements

[Jozef Lawrynowicz via llvm-dev]

Hi,

I thought I would notify the LLVM community about some improvements to
MSP430 support in LLVM/Clang that I'm planning to make.

MCU support
=============
- Update MCU data to the latest version
+ Currently only 161 MCUs are supported, but the latest version of
TI device data describes 609 MCUs.
- Store the CPU version of each MCU
+ Currently only the hardware multiply version of each MCU is
stored; knowledge of the CPU supported by each MCU is required for
future updates.

Support MSP430X code generation (small memory model only)
===========================================================
- Support the -mcpu=msp430x option in Clang
+ This option is accepted by Clang, but doesn't do anything.
Plumbing is required so it enables the MSP430X feature in LLVM,
and passes the correct multilibs to the linker.
- Implement extended shift instructions
+ MSP430X shift instructions such as RRAM and RRAX can shift by
more than one bit position in a single instruction.
+ Currently, multiple shift instructions need to be emitted, each
shifting by one bit position.
- Implement extended PUSH/POP instructions
+ PUSHM/POPM can push and pop multiple registers with a single
instruction.
+ Currently, multiple PUSH/POP instructions need to be emitted, each
pushing or popping one register.
- Implement the RPT flag in the extension word
+ The RPT flag describes how many times an instruction should be
repeated. Up to 16 repeats are supported, and the repeat count can
be hard-coded into the extension word, or stored in a register
described by the extension word.
+ This is mainly used for encoding shifts by amounts not supported
by the more compact R**M instructions.

Check correctness of code generation using the GCC testsuite
==============================================================
- I've used the Embecosm "gcc-for-llvm-testing"[1] repository to run a
subset of GCC's execution tests on MSP430, using the Binutils/GDB
simulator. So far it doesn't seem like anything is critically
broken, but I need to do a full run of the suite and analyze the
results.

In addition to above, I've also implemented ELF object attributes,
currently awaiting review here: <https://reviews.llvm.org/D107969>

Thanks,
Jozef

[1] <https://github.com/embecosm/gcc-for-llvm-testing>

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[Anton Korobeynikov via llvm-dev]

Thanks, Josef!

Contributions to MSP430 are much appreciated and I will be happy to
review them (was on vacations recently and taming the backlog of
emails now).

--
With best regards, Anton Korobeynikov
Department of Statistical Modelling, Saint Petersburg State University

[Jozef Lawrynowicz via llvm-dev]

On Sun, Aug 15, 2021 at 10:33:38PM +0500, Anton Korobeynikov wrote:
> Thanks, Josef!

Hi Anton,

>
> Contributions to MSP430 are much appreciated and I will be happy to
> review them (was on vacations recently and taming the backlog of
> emails now).

Thanks for offering to review the MSP430 patches, it's much appreciated.

Jozef