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

[Matthew Curtis]

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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