[llvm-dev] TableGen trace facility
Madhur Amilkanthwar via llvm-dev
llvm-dev at lists.llvm.org
Wed Aug 5 08:40:35 PDT 2020
There are a bunch of LLVM_DEBUG messages in CodeGenDAGPatterns.cpp. There
are many in Tablegen backends too. In other places you may have to include
headers to use LLVM_DEBUG.
Note, I am talking about Tablegen core which generates .inc files in some
backends (like DAGISel, GlobalISel etc.) which gets included by the
compiler. Hence, these messages will be dumped during .inc generation. As
far as I can imagine, such messages during .inc generation should be able
to unleash the flow. BTW, if you do this exercise, please commit! There are
a very few debug messages Tablegen dumps as of now. Hence, any enhancement
on this line would be a useful addition.
I hope that helps.
On Wed, Aug 5, 2020 at 9:07 PM Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> Hi Paul,
> On Wed, Aug 5, 2020 at 4:04 PM Paul C. Anagnostopoulos
> <paul at windfall.com> wrote:
> > I'm sorry, I still don't understand. I presume you are talking about the
> LLVM_DEBUG() macro that is enabled with the -debug option. But there are no
> uses of LLVM_DEBUG() in the TableGen base files. Wouldn't the base
> "compiler" have to display the information we're talking about? Or is it
> sufficient to use LLVM_DEBUG() in the target-specific files?
> Trying to interpret what Madhur is saying, maybe adding some uses of
> LLVM_DEBUG() to TableGen would be a good idea.
> > At 8/5/2020 08:40 AM, Madhur Amilkanthwar wrote:
> > >Well, I was hinting at LLVM_DEBUG messages. You can pretty much dump
> all "actions" Tablegen would take to process a .td file, which should
> suffice, IMO.
> > >
> > >
> > >On Wed, Aug 5, 2020 at 5:59 PM Paul C. Anagnostopoulos <<mailto:
> paul at windfall.com>paul at windfall.com> wrote:
> > >Your reply suggests that there is a way to see debug messages from
> TableGen. Is that what you meant? If so, can you explain how that works?
> (Sorry, I should know the answer to this question, but I'm quite the
> > >
> > >At 8/5/2020 04:15 AM, Madhur Amilkanthwar wrote:
> > >>Hi Paul,
> > >>If all you care about is debugging then for now we can just emit a few
> more debug messages which would help to "trace" the flow. To distinguish
> traces you can prefix it with some known string. I don't think you really
> need a 'trace' tag in the language spec for this.
> > >>
> > >>Debugging Tablegen has always been a nightmare and I don't think we
> can ever reach a stage where we can start a debugger and debug statements
> in .td files step-by-step. This is far from reality unless we fundamentally
> change the language.
> Lerne, wie die Welt wirklich ist,
> aber vergiss niemals, wie sie sein sollte.
*Disclaimer: Views, concerns, thoughts, questions, ideas expressed in this
mail are of my own and my employer has no take in it. *
Madhur D. Amilkanthwar
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