[PATCH] D54425: [AArch64] Add aarch64_vector_pcs function attribute to Clang

[Sander de Smalen via Phabricator via cfe-commits]

sdesmalen added a subscriber: keith.walker.arm.
sdesmalen added inline comments.


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Comment at: lib/CodeGen/CGDebugInfo.cpp:1101
   case CC_AAPCS:
+  case CC_AArch64VectorCall:
     return llvm::dwarf::DW_CC_LLVM_AAPCS;
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rjmccall wrote:
> rnk wrote:
> > sdesmalen wrote:
> > > I wasn't really sure whether this requires a corresponding DW_CC_LLVM_AAVPCS record in LLVM, as I couldn't find much about the DW_CC_LLVM_  encodings, specifically whether they align with some agreed encoding that is implemented by GDB/LLDB. Is this defined anywhere, or is it ignored by debuggers at the moment?
> > DWARF only allows encoding 256 conventions, and we grabbed 0xC[0-F], I guess for "clang", so we probably want to be careful about adding another. Do you anticipate making debuggers able to call such functions? If not, it's probably not worth it.
> They probably should be callable.
> 
> It looks like DWARF reserves the first 64 conventions for general/language purposes and treats the rest of the range as "user" conventions.   If those conventions are assumed to be universally unique, that's a really limiting schema once you started dividing it up by vendor.  If I might make a suggestion, while there are certainly many calling conventions that are meant to have universal meaning (e.g. most language-specific conventions), there are also a large number that are inherently target-specific.  DWARF already uses a lot of numbers that only make sense in the context of a target (like register numbers); it would make sense for DWARF to carve out a range of the encoding space (maybe 16 or 32 numbers) for target-specific CCs.  This is hardly the first example; consider also all the variant ARM32 CCs or the i386 fastcall CC.
Great feedback. I think this discussion has a wider scope than this patch and I think its probably best to keep this change as-is for now. We'll first work to add a section to the 'DWARF for the ARM 64-bit Architecture' document describing a DW_AT_calling_convention value for the AArch64 vector PCS and will create a separate patch to LLVM/Clang to implement its support. I've also asked @keith.walker.arm to raise this (encoding space) as a topic with the DWARF standardization committee.


https://reviews.llvm.org/D54425