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

[Matthew Curtis]

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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>
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