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

[Alex Susu via llvm-dev]

   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
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