llvm dev - May 2015 - [LLVMdev] RFC: Separate machine IR from lib/CodeGen into lib/MIR

Hi all,

The CodeGen library is a big bag of interdependent bits. This caused
a circular dependency in the MIR serialization commit (r237954), which got
reverted in r238007.

I propose separating the machine IR out of CodeGen and into its own
MIR library, living at lib/MIR. This touches every target but it's mostly a
mechanical change that renames the header files, although a couple of
pre-rename
commits are needed to decouple several things in CodeGen. I've attached a
proof
of concept patch that renames the files and applies cleanly to r238038.

The MIR serialization code will go under the new MIR library and not under
CodeGen which will break the dependency. The CodeGen library will link MIR
automatically so the build files for tools that link with CodeGen won't
have to
be changed.

Thanks for reading,
Alex
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> On 2015-May-26, at 09:46, Alex L <arphaman at gmail.com> wrote:
> 
> Hi all,
> 
> The CodeGen library is a big bag of interdependent bits. This caused
> a circular dependency in the MIR serialization commit (r237954), which got
> reverted in r238007.
> 
> I propose separating the machine IR out of CodeGen and into its own
> MIR library, living at lib/MIR. This touches every target but it's
mostly a
> mechanical change that renames the header files, although a couple of
pre-rename
> commits are needed to decouple several things in CodeGen. I've attached
a proof
> of concept patch that renames the files and applies cleanly to r238038.
> 
> The MIR serialization code will go under the new MIR library and not under
> CodeGen which will break the dependency. The CodeGen library will link MIR
> automatically so the build files for tools that link with CodeGen won't
have to
> be changed.
> 
> Thanks for reading,
> Alex
> 
FWIW, I'm in favour of this.  I'd be interested to hear if there's
a reason *not* to do this.

Here's some more context:

 
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20150518/278031.html

> On May 26, 2015, at 1:37 PM, Duncan P. N. Exon Smith <dexonsmith at
apple.com> wrote:
> 
>> 
>> On 2015-May-26, at 09:46, Alex L <arphaman at gmail.com> wrote:
>> 
>> Hi all,
>> 
>> The CodeGen library is a big bag of interdependent bits. This caused
>> a circular dependency in the MIR serialization commit (r237954), which
got
>> reverted in r238007.
>> 
>> I propose separating the machine IR out of CodeGen and into its own
>> MIR library, living at lib/MIR. This touches every target but it's
mostly a
>> mechanical change that renames the header files, although a couple of
pre-rename
>> commits are needed to decouple several things in CodeGen. I've
attached a proof
>> of concept patch that renames the files and applies cleanly to r238038.
>> 
>> The MIR serialization code will go under the new MIR library and not
under
>> CodeGen which will break the dependency. The CodeGen library will link
MIR
>> automatically so the build files for tools that link with CodeGen
won't have to
>> be changed.
>> 
>> Thanks for reading,
>> Alex
>> 
> 
> FWIW, I'm in favour of this.  I'd be interested to hear if
there's
> a reason *not* to do this.
> 
> Here's some more context:
> 
> 
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20150518/278031.html
<http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20150518/278031.html>
I have no objections, though I think lib/MachineIR would make a prettier
bikeshed ;-)

—Owen
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