Arnold Schwaighofer 3ae6d7cb4d runtime/IRGen: return the argument from swift_retain family of functions ...

On architectures where the calling convention uses the same argument register as
return register this allows the argument register to be live through the calls.

We use LLVM's 'returned' attribute on the parameter to facilitate this.

We used to perform this optimization via an optimization pass. This was ripped
out some time ago around commit 955e4ed652.
By using LLVM's 'returned' attribute on swift_*retain, we get the same
optimization from the LLVM backend.

2017-09-19 07:16:37 -07:00

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