[PATCH] Add a flag to experiment with outlining optional branches.

[Daniel Jasper]

Ah right.

Well, it might be too limiting, but it might be a good incremental step.
Any further suggestions are definitely welcome.

On Wed, Mar 4, 2015 at 9:04 AM, Xinliang David Li <xinliangli at gmail.com>
wrote:

> The example mentioned has a diamond shape. Besides within the 'then' arm
> of cond1 branch, there could be multiple consecutive 'if (cond_x) B_x'
> where B_x blocks are cold. The heuristic in your patch seems to be too
> limiting.
>
> David
>
> On Tue, Mar 3, 2015 at 11:19 PM, Daniel Jasper <djasper at google.com> wrote:
>
>> Yes. The reasoning is that in this case the entire branch (containing A,
>> B and C) will already be outlined and we don't want to fragment this
>> further. In initial benchmarks, this seemed to have a slight benefit over
>> additionally outlining B. Lots of stuff we can investigate, though.
>>
>> On Wed, Mar 4, 2015 at 8:03 AM, Xinliang David Li <xinliangli at gmail.com>
>> wrote:
>>
>>> If I read the change correctly,  'B' block in the following case can not
>>> be outlined. Is it intended?
>>>
>>> David
>>>
>>> if (cond1) {
>>>     A
>>>     if (cond2) {
>>>
>>>          B
>>>      }
>>>     C
>>>     ...
>>> }
>>> else {
>>>    D
>>> }
>>>
>>> On Tue, Mar 3, 2015 at 10:46 PM, Daniel Jasper <djasper at google.com>
>>> wrote:
>>>
>>>> Re-add the test.
>>>>
>>>>
>>>> http://reviews.llvm.org/D7719
>>>>
>>>> Files:
>>>>   lib/CodeGen/MachineBlockPlacement.cpp
>>>>   test/CodeGen/X86/code_placement_outline_optional_branches.ll
>>>>
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>>>
>>
>
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