[PATCH] Teach DeadArgElimination not to eliminate return values of functions with 'returned' arguments

[Dan Gohman]

On Thu, Jun 20, 2013 at 3:36 PM, Stephen Lin <swlin at post.harvard.edu> wrote:

> Hi,
>
> This patch makes the DeadArgElimination IPO pass treat any return
> value of any function with a 'returned' argument as live even if there
> are no uses. This is meant to allow the clang patch committed as
> revision r184205 (and subsequent minor fixes) to be recommitted after
> being reverted in revision r184205 due to broken builds on ARM when
> compiling with LTO.
>

This does conflict with the theoretical separation of concerns between
optimizer and codegen in LLVM though. This patch does not promote
subsequent mid-level optimization opportunities; treating values as live
when they are actually unused may actually obscure other mid-level
optimization opportunities.

Dan
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