[llvm] r202304 - Add a limit to the heuristic that register allocates instructions in local order.

[Andrew Trick]

On Feb 27, 2014, at 4:25 AM, Renato Golin <renato.golin at linaro.org> wrote:

> On 27 February 2014 10:05, Renato Golin <renato.golin at linaro.org> wrote:
>> I believe your patch broke a test on ARM's test-suite:
> 
> Hi Andrew,
> 
> Now I'm sure of it. ;)
> 
> I just reverted your patch and the test passes again. How do you want
> to proceed about this?

Thanks for drawing this to my attention. This change disables a recent heuristic in some cases, reverting back to the original behavior. I can't reproduce with a cross compiler (doesn’t really mean anything though since it is a different platform), and haven't seen any failures on our internal armv7 lnt runs.

I think we either have:

- A bug in the host compiler on that builder.

- A recent bug in CodeGen that has been hidden by that heuristic and is now exposed.

Reverting would certainly only hide whatever the issue is.

Here are some options:

1. You could try to reproduce compiling RegAllocGreedy at O0.

2. You could try a different host compiler.

3. I can temporarily disable this change on armv7 using a target hook and file a PR.

Let me know if I should ahead with #3. It seems a little drastic until we have reason to believe the host compiler is good.

Thanks!
-Andy

> 
> cheers,
> --renato