llvm dev - Aug 2016 - Initial selection DAG creation (SelectionDAG.cpp) - output detailed debug info

Hello.
     In order to detect a problem in the initial selection DAG creation that I
have in my
back end I need to output detailed debug info from the SelectionDAG.cpp module
with all
the TableGen records that are being processed, and compare between a working
back end and
my buggy back end.

     I can debug by adding myself DEBUG() statements in the visit*() methods of
the
SelectionDAG.cpp module or by using GDB on this module.
     Did anybody try a better way for debugging the selection DAG creation
within the
SelectionDAG.cpp module?

   Thank you,
     Alex

I think the "initial selection DAG" building process should be target
independent. After that, there is DAG combining, legalization, instruction
selection and scheduling all of which are at least partially
target-dependent.

As far as TableGen records, the ones from your target should really only be
consulted as part of instruction selection and scheduling as far as I'm
aware. And the DAG instruction selector will actually output information
about which record it is using for the match and if it does not match, it
mentions the index where the match failed.

N

On Wed, Aug 3, 2016 at 3:05 AM, Alex Susu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>   Hello.
>     In order to detect a problem in the initial selection DAG creation
> that I have in my back end I need to output detailed debug info from the
> SelectionDAG.cpp module with all the TableGen records that are being
> processed, and compare between a working back end and my buggy back end.
>
>     I can debug by adding myself DEBUG() statements in the visit*()
> methods of the SelectionDAG.cpp module or by using GDB on this module.
>     Did anybody try a better way for debugging the selection DAG creation
> within the SelectionDAG.cpp module?
>
>   Thank you,
>     Alex
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Hello.
     Thank you for your comments.
     I just realized that I wrote in the previous email SelectionDAG.cpp instead
of
SelectionDAGBuilder.cpp .
     I managed to solve this issue by simply adding about 20 DEBUG() statements
in the
sensitive parts of SelectionDAGBuilder.cpp .

     It turned out that the SelectionDAGBuilder class, responsible for creating
the
initial selection DAG, uses the TargetLoweringInfo class, which contains target
dependent
info like number and size of registers, parameter passing conventions, etc,
resulting in
eventual splitting of constant vectors to accommodate the width of the SIMD
unit, etc.
      Cardoso Lopes and Auler's "Getting started with LLVM core
libraries" book talks in
Chapter 6, (for example, page 150) about this.

   Best regards,
     Alex

On 8/4/2016 10:09 AM, Nemanja Ivanovic wrote:
> I think the "initial selection DAG" building process should be
target independent. After
> that, there is DAG combining, legalization, instruction selection and
scheduling all of
> which are at least partially target-dependent.
>
> As far as TableGen records, the ones from your target should really only be
consulted as
> part of instruction selection and scheduling as far as I'm aware. And
the DAG instruction
> selector will actually output information about which record it is using
for the match and
> if it does not match, it mentions the index where the match failed.
>
> N
>
> On Wed, Aug 3, 2016 at 3:05 AM, Alex Susu via llvm-dev <llvm-dev at
lists.llvm.org
> <mailto:llvm-dev at lists.llvm.org>> wrote:
>
>        Hello.
>          In order to detect a problem in the initial selection DAG creation
that I have in
>     my back end I need to output detailed debug info from the
SelectionDAG.cpp module with
>     all the TableGen records that are being processed, and compare between
a working back
>     end and my buggy back end.
>
>          I can debug by adding myself DEBUG() statements in the visit*()
methods of the
>     SelectionDAG.cpp module or by using GDB on this module.
>          Did anybody try a better way for debugging the selection DAG
creation within the
>     SelectionDAG.cpp module?
>
>        Thank you,
>          Alex
>     _______________________________________________
>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>     http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>