[PATCH] Change order of tablegen generated fastisel instruction code to be based on instruction complexity

[Eric Christopher]

Ah, thanks Hal.

LGTM then with the comment change.

-eric

On Thu Nov 13 2014 at 3:09:59 PM Hal Finkel <hfinkel at anl.gov> wrote:

> ----- Original Message -----
> > From: "Bill Seurer" <seurer at linux.vnet.ibm.com>
> > To: seurer at linux.vnet.ibm.com, hfinkel at anl.gov, echristo at gmail.com,
> wschmidt at linux.vnet.ibm.com
> > Cc: llvm-commits at cs.uiuc.edu
> > Sent: Thursday, November 13, 2014 4:57:55 PM
> > Subject: Re: [PATCH] Change order of tablegen generated fastisel
> instruction code to be based on instruction
> > complexity
> >
> > ================
> > Comment at:
> > /home/seurer/llvm/llvm-oneoff/utils/TableGen/FastISelEmitter.cpp:595
> > @@ -570,2 +594,3 @@
> >
> > -    SimplePatterns[Operands][OpcodeName][VT][RetVT][PredicateCheck]
> > = Memo;
> > +// This was used when testing
> > +//    if
> > (SimplePatterns[Operands][OpcodeName][VT][RetVT].count(complexity))
> > {
> > ----------------
> > echristo wrote:
> > > seurer wrote:
> > > > echristo wrote:
> > > > > Is there a reason we either a) don't want this on by default,
> > > > > or b) would never want this on?
> > > > When I tried it generated over 150 warnings so it's probably just
> > > > too noisy.  I wasn't sure if multiple patterns having the same
> > > > complexity could be a potential issue, though.
> > > Yeah, I don't think so. Go ahead and just delete the commented out
> > > code with a "Two patterns could have the same complexity and we
> > > just end up picking the first one" or something like that. (I
> > > think it's the first one at this point?)
> > They all will still be generated because the predicates are
> > different.  I believe the order will be the order in which they are
> > encountered.
> >
> > "When iterating over a std::multimap the elements are ordered by key,
> > but the order of elements having the same key is not specified."
> >
> > Hmmm, maybe not.
>
> It was unspecified in C++ before C++11, but since C++11, the order is
> specified to be stable. LLVM has other dependencies on this, IIRC.
>
> http://stackoverflow.com/questions/2643473/does-stdmultiset-guarantee-
> insertion-order?rq=1
>
>  -Hal
>
> >
> > http://reviews.llvm.org/D6220
> >
> >
> >
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
>
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