[PATCH] D117725: [AVR] Fix atomicrmw result value

[Ayke via Phabricator via llvm-commits]

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This patch fixes the atomicrmw result value to be the value before the operation instead of the value after the operation. This was a bug, left as a FIXME in the code (see D97127 <https://reviews.llvm.org/D97127>).

>From the LangRef:

> The contents of memory at the location specified by the `‘<pointer>’` operand are atomically read, modified, and written back. The original value at the location is returned.

Doing this expansion early allows the register allocator to arrange registers in such a way that commutable operations are simply swapped around as needed, which results in shorter code while still being correct.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D117725

Files:
  llvm/lib/Target/AVR/AVRExpandPseudoInsts.cpp
  llvm/lib/Target/AVR/AVRISelLowering.cpp
  llvm/lib/Target/AVR/AVRISelLowering.h
  llvm/lib/Target/AVR/AVRInstrInfo.td
  llvm/test/CodeGen/AVR/atomics/load16.ll
  llvm/test/CodeGen/AVR/atomics/load8.ll

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