[PATCH] Fix miscompile due to StackColoring incorrectly merging stack slots

[Nadav Rotem]

Hi Mark, 

Thanks for catching this. This change LGTM. 

Nadav

On May 15, 2013, at 11:23 AM, Mark Seaborn <mseaborn at chromium.org> wrote:

> Fix miscompile due to StackColoring incorrectly merging stack slots
> 
> IR optimisation passes can result in a basic block that contains:
> 
>   llvm.lifetime.start(%buf)
>   ...
>   llvm.lifetime.end(%buf)
>   ...
>   llvm.lifetime.start(%buf)
> 
> Before this change, calculateLiveIntervals() was ignoring the second
> lifetime.start() and was regarding %buf as being dead from the
> lifetime.end() through to the end of the basic block.  This can cause
> StackColoring to incorrectly merge %buf with another stack slot.
> 
> Fix by removing the incorrect Starts[pos].isValid() and
> Finishes[pos].isValid() checks.
> 
> Just doing:
>       Starts[pos] = Indexes->getMBBStartIdx(MBB);
>       Finishes[pos] = Indexes->getMBBEndIdx(MBB);
> unconditionally would be enough to fix the bug, but it causes some
> test failures due to stack slots not being merged when they were
> before.  So, in order to keep the existing tests passing, treat LiveIn
> and LiveOut separately rather than approximating the live ranges by
> merging LiveIn and LiveOut.
> 
> This fixes PR15707.
> 
> <Mail Attachment>

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