[PATCH] D68524: [AVR] Rewrite the function calling convention.

[Dylan McKay via Phabricator via llvm-commits]

dylanmckay added a comment.

Committed in

  b9c26a9cfe53da7ef96e13ef1aa7fe793b1b5d28
  commit b9c26a9cfe53da7ef96e13ef1aa7fe793b1b5d28
  Author: Dylan McKay <me at dylanmckay.io>
  Date:   Fri Jun 19 23:26:00 2020 +1200
  
      [AVR] Rewrite the function calling convention.
      
      Summary:
      The previous version relied on the standard calling convention using
      std::reverse() to try to force the AVR ABI. But this only works for
      simple cases, it fails for example with aggregate types.
      
      This patch rewrites the calling convention with custom C++ code, that
      implements the ABI defined in https://gcc.gnu.org/wiki/avr-gcc.
      
      To do that it adds a few 16-bit pseudo registers for unaligned argument
      passing, such as R24R23. For example this function:
      
          define void @fun({ i8, i16 } %a)
      
      will pass %a.0 in R22 and %a.1 in R24R23.
      
      There are no instructions that can use these pseudo registers, so a new
      register class, DREGSMOVW, is defined to make them apart.
      
      Also the ArgCC_AVR_BUILTIN_DIV is no longer necessary, as it is
      identical to the C++ behavior (actually the clobber list is more strict
      for __div* functions, but that is currently unimplemented).
      
      Reviewers: dylanmckay
      
      Subscribers: Gaelan, Sh4rK, indirect, jwagen, efriedma, dsprenkels, hiraditya, Jim, llvm-commits
      
      Tags: #llvm
      
      Differential Revision: https://reviews.llvm.org/D68524
      
      Patch by Rodrigo Rivas Costa.


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D68524