[llvm] r231186 - RegisterCoalescer: Gracefully continue if subrange merging fails.

[Quentin Colombet]

With the in-tree target this not exposed.

Arguably we could create a fake target with such problem, but I do not think this is worth the complexity.

Q.
 
> On Mar 3, 2015, at 5:21 PM, Chandler Carruth <chandlerc at google.com> wrote:
> 
> 
> On Tue, Mar 3, 2015 at 4:43 PM, Matthias Braun <matze at braunis.de <mailto:matze at braunis.de>> wrote:
> Author: matze
> Date: Tue Mar  3 18:43:50 2015
> New Revision: 231186
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=231186&view=rev <http://llvm.org/viewvc/llvm-project?rev=231186&view=rev>
> Log:
> RegisterCoalescer: Gracefully continue if subrange merging fails.
> 
> There is a known bug where the register coalescer fails to merge
> subranges when multiple ranges end up in the "overflow" bit 32 of the
> lanemasks. A proper fix for this is complicated so for now this is a
> workaround which lets the register coalescer drop the subregister
> liveness information (we just loose some precision by that) and
> continue.
> 
> Modified:
>     llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
> 
> No test case? This seems like something really important to cover...
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