[PATCH] Add getters for Pass IDs used by Polly plug-in.

[Matthew Curtis]

Ping.

On 2/20/2013 7:01 AM, Matthew Curtis wrote:
> Ping.
>
> On 2/11/2013 7:35 AM, Matthew Curtis wrote:
>> Ping.
>>
>> On 2/6/2013 8:15 AM, Matthew Curtis wrote:
>>> Hello all,
>>>
>>> This patch helps resolve a couple of issues we encountered while
>>> porting the Polly plug-in to Windows.
>>>
>>> The Polly plugin depends on some LLVM Passes which it identifies via
>>> Pass IDs. Pass IDs are implemented as the address of a static member
>>> variable (ID) of the Pass. On Windows however, there seems to be a bug
>>> in the Visual Studio compiler or linker that results in multiple
>>> dll-local copies of this data when referenced directly. The result is
>>> that Polly is unable to locate Passes that are part of the executable
>>> it is being loaded into.
>>>
>>> As a work around, this patch adds getters (GetClassPassID) for the
>>> Pass IDs used by Polly. The symbols for the globals are not
>>> exported. The getters are exported and Polly uses them instead.
>>>
>>> Removing use of global data by the Polly plug-in also makes it
>>> possible to delay load LLVM symbols from the containing executable
>>> which in turn removes the restriction that the executable have a
>>> specific name (determined at link-time).
>>>
>>> We also considered a couple alternatives to this minimal patch:
>>>
>>> 1) Update *all* Passes to provide GetClassPassID in lieu of ID.
>>>
>>>    This leaves the code in the cleanest state and would be a good
>>>    choice if starting from scratch. However I started implementing it
>>>    and it turns out to have a very large ripple effect. Not only does
>>>    it require changing a large number of files in LLVM, but it breaks
>>>    source compatibility for passes that are not part of the LLVM
>>>    source.
>>>
>>>    That being said, I'd be willing to do the work if everyone thinks
>>>    that's the right thing to do and we're willing break source
>>>    compatibility.
>>>
>>>    Perhaps we could ease the pain by deprecating ID for some time
>>>    before removing it.
>>>
>>> 2) Add GetClassPassID to Passes accessible by plug-ins (i.e. those
>>>    under include/llvm), but leave ID as it is.
>>>
>>>    As with the proposed patch, this may cause confusion because there
>>>    are multiple ways of getting a Pass's ID. But at least it's not
>>>    specific to the Polly plug-in and other plug-ins on Windows may
>>>    benefit.
>>>
>>> Thanks,
>>> Matthew Curtis
>>>
>>> BTW, there's a brief related discussion on llvm-dev here:
>>> http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-January/058838.html
>>> http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-February/thread.html#58982 
>>>
>>>
>>>
>>>
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>>> llvm-commits mailing list
>>> llvm-commits at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>
>>
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