indirect calls are always used (LLVM-321)

[yamt]

currently, -mlongcalls is always effectively on.
i had to patch llvm for my use case. cf. yamt@3f04244
it would be nicer to have a way to use direct calls.
ideally, the backend can automatically choose direct calls when the call distance is not too long, i guess.

related:
bytecodealliance/wasm-micro-runtime#3141
bytecodealliance/wasm-micro-runtime#3142

[yamt]

for my use case, it's ok to manually adding attributes at IR level. eg. xtensa-short-call.
mips has something along the line: https://clang.llvm.org/docs/AttributeReference.html#short-call-near

[gerekon]

@yamt Thanks for pointing this out. We are working on direct calls support using callN instruction.

cc @sstefan1

[sstefan1]

for my use case, it's ok to manually adding attributes at IR level. eg. xtensa-short-call. mips has something along the line: https://clang.llvm.org/docs/AttributeReference.html#short-call-near

We're working on implementing the support for direct calls, the same way gcc does it. That is a bit more complex. In the mean time we can implement short-call attributes for xtensa.

[dongsheng28849455]

hi, @sstefan1, can I ask the progress for this feature?

[sstefan1]

hi, @sstefan1, can I ask the progress for this feature?

There hasn't been any real progress since that coment. I'll write here when I have some updates.

[dongsheng28849455]

hi, @sstefan1, can I ask the progress for this feature?

There hasn't been any real progress since that coment. I'll write here when I have some updates.

is that fixed by https://github.com/espressif/llvm-project/releases/tag/esp-17.0.1_20240408?

[yamt]

hi, @sstefan1, can I ask the progress for this feature?

There hasn't been any real progress since that coment. I'll write here when I have some updates.

is that fixed by https://github.com/espressif/llvm-project/releases/tag/esp-17.0.1_20240408?

the short-call attribute is already in the releases and it seems working as far as i tested.
the "ideal" solution (ie. somehow automatically use short/long calls) is not there yet.
i guess he was talking about the latter.

[gerekon]

hi, @sstefan1, can I ask the progress for this feature?

There hasn't been any real progress since that coment. I'll write here when I have some updates.

is that fixed by https://github.com/espressif/llvm-project/releases/tag/esp-17.0.1_20240408?

the short-call attribute is already in the releases and it seems working as far as i tested. the "ideal" solution (ie. somehow automatically use short/long calls) is not there yet. i guess he was talking about the latter.

Yes, exactly. Automatic use of short/long calls is in progress.
Just for information: We do not expect it to be ready in the 1st half of this year.

[andyross]

Just bumped into this myself. Is there no support for at least changing the default e.g. ("-mno-longcalls")? The range of a CALLx instruction is +/- 512k, which is quite a bit larger than the .text segment of many/most firmware images in the wild. Right now the conservative default is a pretty severe performance regression, and it's needless for a lot of applications.

[andreisfr]

@andyross , thank you for the question. Currently we work on implementing CALLX support in the LLD.