[cfe-dev] [llvm-dev] MLIR for clang

C Bergström via cfe-dev cfe-dev at lists.llvm.org
Mon Feb 17 09:46:12 PST 2020

When you actually start to solve and implement this you'll find that "LLVM
IR" is actually mid-whirl on an almost 1:1 basis. (super close). However,
we don't exactly do IR<>IR translation and instead hook in at an API level.
So it's more matching constructs and trying to "get in where you fit in".
Since we had overlapping mid-whirl optimizations we had to figure out which
to turn on/off on each side.

We also skipped VH Whirl for a number of reasons and just kinda cut it out.
I don't think Fred is subscribed to the list, but he isn't the only smart
person who worked on the compiler. There were a few managers, brilliant
people and unsung heroes who worked at SGI.

Dror Maydan and Sun Chan were more intimately involved with the actual
implementation of loop optimizations iirc. Fred's best known for his low
level codegen work and overall vision of compiler architecture.

On Tue, Feb 18, 2020 at 1:24 AM Prashanth N R via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Fred Chow is a well known name in compiler community. He was the architect
> of Open64 compiler.
> His comment on LLVM IR from open64 mailing list can be seen at :
> https://sourceforge.net/p/open64/mailman/message/23829398/
> " From their name, LLVM roughly corresponds to Low WHIRL. I wonder how
> LLVM tackles the compilation problems Open64 has tackled.  People with
> exposure to LLVM are welcome to chime in."
> On Mon, Feb 17, 2020 at 10:43 PM Prashanth N R <prashanth.nr at gmail.com>
> wrote:
>> Currently LLVM uses a low level IR for representing programs. Memory
>> disambiguation does not happen accurately for constructs like
>> multi-dimensional arrays.  One of the ways we alleviate the same in LLVM
>> currently is by using multiversioning of the code. By supporting a
>> mid-level IR like MLIR we intend to keep the access indices of
>> multidimensional array and do better disambiguation.
>> thanks,
>> -Prashanth
>> On Sun, Feb 16, 2020 at 4:34 PM Nicolai Hähnle <nhaehnle at gmail.com>
>> wrote:
>>> Hi Prashanth,
>>> On Sun, Feb 16, 2020 at 10:22 AM Prashanth N R via llvm-dev
>>> <llvm-dev at lists.llvm.org> wrote:
>>> >>   Starting from May-June, we at "Compiler Tree" would  start porting
>>> clang compiler to use MLIR as middle end target. If someone has already
>>> started a similar effort we would love to collaborate with them. If someone
>>> would like to work with us, we are ready to form a group and collaborate.
>>> If there are sharing opportunities from Fortran side, we would like to
>>> consider the same.\
>>> That's a rather vague statement, considering the flexibility of MLIR.
>>> Could you explain your plans in more detail, and what specifically you
>>> hope to achieve with them?
>>> Cheers,
>>> Nicolai
>>> >>
>>> >>    We are in the early phase of design for "C" part of the work. From
>>> our experience with (FC+MLIR) compiler, we are estimating that we would
>>> have an early cut of the compiler working with non-trivial workload within
>>> a quarter of starting of work.
>>> >>
>>> >>   Please ping me for any queries or concerns.
>>> >>
>>> >> Regards,
>>> >> -Prashanth
>>> >
>>> > _______________________________________________
>>> > LLVM Developers mailing list
>>> > llvm-dev at lists.llvm.org
>>> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>> --
>>> Lerne, wie die Welt wirklich ist,
>>> aber vergiss niemals, wie sie sein sollte.
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