[RFC] Case insensitive assembly directives for all targets

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#1

Hi all,

In response to this issue[0] on Bugzilla, I recently committed changes to make assembly directives case insensitive for generic directives and their aliases[1], ARM[2] and AArch64[3]. (since those are the targets I have knowledge of)

I realise this was probably a bit too hasty of me, so I’m writing this to gather feedback on how to proceed.

Some concerns were raised that it may be easier to fix projects that aren’t using lower case directives. My intent was more to remove our reliance on case in general, which is more an implementation detail than a feature as far as I can tell. Maybe this is not a strong enough argument for change.

No target in llvm uses anything but lower case directives. Some targets supported by GCC/binutils do document mixed case directives, but accept any case.

So my questions for the list are:

  • do you agree with the changes so far? (happy to revert if not)

  • should the same changes be applied to other targets?

  • could there be future situations where a target would need case specific directives?

  • Where should this behaviour (whatever it ends up as) be documented? I found [4] but it’s more about extensions than the assembler as such.

Thanks,
David Spickett.

[0] https://bugs.llvm.org/show_bug.cgi?id=39527
[1] https://reviews.llvm.org/D72686
[2] https://reviews.llvm.org/D73469
[3] https://reviews.llvm.org/D72923
[4] https://llvm.org/docs/Extensions.html

#2

do you agree with the changes so far?
Yes, if GAS is case-insensitive for directives, then requiring them to be lower-case in LLVM is a needless incompatibility.

should the same changes be applied to other targets?
I don’t have any experience with targets other than ARM and AArch64 either, but being consistent between targets, and between LLVM and GAS, both seem like positives.

could there be future situations where a target would need case specific directives?
That would imply that there are two directives which differ only in case, but do different things, which I’d prefer we avoid. If we had to do this, for example for GAS compatibility, then we could put in an exception (as GAS would surely also have to do).

Where should this behaviour (whatever it ends up as) be documented?
We don’t currently have much (maybe even any) documentation for the LLVM/clang assembler, we mostly just rely on being compatible with GAS. Maybe that’s something that we should change, but it’s a much bigger issue than this. I don’t think there’s any point in documenting that we do the same thing as GAS in this one corner case, when GAS compatibility is generally assumed.

Oliver

#3

+1 to all of what Oliver said. We aim for compatibility with GNU in most (all?) of our other binutils, so why should the assembler be any different?