[llvm-dev] [MSP430] Plans for MSP430 improvements (original) (raw)

Jozef Lawrynowicz via llvm-dev llvm-dev at lists.llvm.org
Sun Aug 15 07:39:23 PDT 2021

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 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.

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