[llvm-commits] [LLVMdev] FW: RFC: Supporting different sized address space arithmetic

[Eli Friedman]

On Wed, Oct 3, 2012 at 8:13 AM, Villmow, Micah <Micah.Villmow at amd.com> wrote:
> Ahh, ok. Well from what I can tell, what would be considered an illegal address space?
> Since this new, I guess we have to define it.
> Can negative address spaces be illegal, or wrap around to a very large value?
> What is the largest value that is legal, can we limit it to 10 bits?

It looks like it's currently limited to 24 bits; if you're picking
something arbitrarily, might as well pick that.  Negative address
spaces should be illegal.

-Eli

> Micah
>
>> -----Original Message-----
>> From: Eli Friedman [mailto:eli.friedman at gmail.com]
>> Sent: Tuesday, October 02, 2012 6:14 PM
>> To: Villmow, Micah
>> Cc: llvm-commits at cs.uiuc.edu LLVM
>> Subject: Re: [LLVMdev] FW: RFC: Supporting different sized address
>> space arithmetic
>>
>> On Tue, Oct 2, 2012 at 4:06 PM, Villmow, Micah <Micah.Villmow at amd.com>
>> wrote:
>> > At this point I believe the assumption is that the data layout is
>> valid as error checking should be at TargetData creation and not when
>> the DataLayout string is emitted.
>>
>> Oh, err, sorry, I didn't actually mean to ask that.  I was wondering
>> about error checking in your changes to the data layout parsing
>> routines.
>>
>> -Eli
>>
>> > I'll make sure the pointers are printed out in sorted order and
>> submit another patch.
>> >
>> >> -----Original Message-----
>> >> From: Eli Friedman [mailto:eli.friedman at gmail.com]
>> >> Sent: Tuesday, October 02, 2012 2:52 PM
>> >> To: Villmow, Micah
>> >> Cc: llvm-commits at cs.uiuc.edu LLVM
>> >> Subject: Re: [LLVMdev] FW: RFC: Supporting different sized address
>> space
>> >> arithmetic
>> >>
>> >> +  for (DenseMap<unsigned, PointerAlignElem>::const_iterator
>> >> +      pib = Pointers.begin(), pie = Pointers.end();
>> >> +      pib != pie; ++pib) {
>> >> +    const PointerAlignElem &PI = pib->second;
>> >> +    OS << "-p";
>> >> +    if (PI.AddressSpace) {
>> >> +      OS << PI.AddressSpace;
>> >> +    }
>> >> +     OS << ":" << PI.TypeBitWidth*8 << ':' << PI.ABIAlign*8
>> >> +        << ':' << PI.PrefAlign*8;
>> >>
>> >> Don't iterate over a DenseMap like this; the iteration order is
>> >> unspecified.
>> >>
>> >> How does the error checking for invalid data layouts work?  It seems
>> >> like there's some missing checks here.
>> >>
>> >> Otherwise, looks fine.
>> >>
>> >> -Eli
>> >>
>> >> On Tue, Oct 2, 2012 at 9:57 AM, Villmow, Micah
>> <Micah.Villmow at amd.com>
>> >> wrote:
>> >> > Ping!
>> >> >
>> >> >> -----Original Message-----
>> >> >> From: Villmow, Micah
>> >> >> Sent: Thursday, September 27, 2012 9:52 AM
>> >> >> To: Villmow, Micah; Eli Friedman
>> >> >> Cc: LLVM Developers Mail
>> >> >> Subject: RE: [LLVMdev] FW: RFC: Supporting different sized
>> address
>> >> >> space arithmetic
>> >> >>
>> >> >> Since the TargetData/Bitcast issue is on hold pending an LLVM dev
>> >> >> meeting BOF it seems, I am revisiting this patch.
>> >> >>
>> >> >> This should have no functional changes, but only allow LLVM to
>> >> >> understand different pointer sizes for the backends that wish to
>> use
>> >> it.
>> >> >>
>> >> >> Micah
>> >> >>
>> >> >> > -----Original Message-----
>> >> >> > From: llvmdev-bounces at cs.uiuc.edu
>> >> >> > [mailto:llvmdev-bounces at cs.uiuc.edu]
>> >> >> > On Behalf Of Villmow, Micah
>> >> >> > Sent: Thursday, September 06, 2012 9:19 AM
>> >> >> > To: Eli Friedman
>> >> >> > Cc: LLVM Developers Mail
>> >> >> > Subject: Re: [LLVMdev] FW: RFC: Supporting different sized
>> address
>> >> >> > space arithmetic
>> >> >> >
>> >> >> > Doh! hit send too soon, patch attached.
>> >> >> >
>> >> >> > > -----Original Message-----
>> >> >> > > From: Villmow, Micah
>> >> >> > > Sent: Thursday, September 06, 2012 9:17 AM
>> >> >> > > To: 'Eli Friedman'
>> >> >> > > Cc: LLVM Developers Mail
>> >> >> > > Subject: RE: [LLVMdev] FW: RFC: Supporting different sized
>> >> >> > > address space arithmetic
>> >> >> > >
>> >> >> > > Eli,
>> >> >> > >  Here is the first of many patches that adds support for
>> >> >> > > specifying different pointer sizes for different address
>> spaces.
>> >> >> > > This is only the modifications to TargetData and not all the
>> >> >> > > changes to the backends/optimizers. There should be no
>> functional
>> >> >> > > changes here since the default value is what the current
>> value
>> >> is.
>> >> >> > >
>> >> >> > > After this is approved, my goal is the following:
>> >> >> > > 1) Add a few interfaces to various functions that simplify
>> >> >> > > retrieving address space information.
>> >> >> > > 2) Update all of the optimizations to use address space
>> >> >> > > information when querying the pointer type.
>> >> >> > > 3) Update the backends to follow suite
>> >> >> > > 4) Update the clients(clang, etc..) to use the correct API.
>> >> >> > > 5) remove the default arguments so that future users must
>> >> >> > > explicitly specify an address space.
>> >> >> > >
>> >> >> > > I'm not sure how to add tests for this since no backend uses
>> it
>> >> >> > > yet, but i'll try to figure something out.
>> >> >> > > Micah
>> >> >> > > > -----Original Message-----
>> >> >> > > > From: Eli Friedman [mailto:eli.friedman at gmail.com]
>> >> >> > > > Sent: Thursday, August 30, 2012 3:43 PM
>> >> >> > > > To: Villmow, Micah
>> >> >> > > > Cc: LLVM Developers Mail
>> >> >> > > > Subject: Re: [LLVMdev] FW: RFC: Supporting different sized
>> >> >> > > > address space arithmetic
>> >> >> > > >
>> >> >> > > > On Thu, Aug 30, 2012 at 3:27 PM, Villmow, Micah
>> >> >> > > > <Micah.Villmow at amd.com>
>> >> >> > > > wrote:
>> >> >> > > > >
>> >> >> > > > >
>> >> >> > > > >> -----Original Message-----
>> >> >> > > > >> From: Eli Friedman [mailto:eli.friedman at gmail.com]
>> >> >> > > > >> Sent: Thursday, August 30, 2012 3:03 PM
>> >> >> > > > >> To: Villmow, Micah
>> >> >> > > > >> Cc: LLVM Developers Mail
>> >> >> > > > >> Subject: Re: [LLVMdev] FW: RFC: Supporting different
>> sized
>> >> >> > > > >> address space arithmetic
>> >> >> > > > >>
>> >> >> > > > >> On Thu, Aug 30, 2012 at 2:38 PM, Villmow, Micah
>> >> >> > > > >> <Micah.Villmow at amd.com>
>> >> >> > > > >> wrote:
>> >> >> > > > >> > Eli,
>> >> >> > > > >> >  Here is an updated patch. This is a lot smaller based
>> on
>> >> >> > > > >> > your
>> >> >> > > > >> feedback and still solves the same problem.
>> >> >> > > > >>
>> >> >> > > > >> The patch appears to be corrupt; can you regenerate it?
>> >> >> > > > > [Villmow, Micah] Attached.
>> >> >> > > > >>
>> >> >> > > > >> > For your comment on the IR changes, I'm reluctant to
>> >> >> > > > >> > introduce changes
>> >> >> > > > >> there because really the backend is overriding the
>> default
>> >> >> > > > >> behavior at a device specific level. The optimizations
>> >> >> > > > >> themselves can be dangerous, but still should produce
>> >> >> > > > >> correct results, this only allows the backend to
>> optimize
>> >> >> > > > >> certain cases
>> >> >> and is opt-in.
>> >> >> > > > >>
>> >> >> > > > >> Suppose I have an array of ten pointers into some
>> >> >> > > > >> address-space which uses 16-bit pointers, and the
>> default
>> >> >> > > > >> pointer size is 64 bits.  How many bytes in memory does
>> that
>> >> >> > > > >> take?  To me, it seems like the obvious answer is 20
>> bytes,
>> >> >> > > > >> but if you compute it using our current TargetData,
>> you'll
>> >> >> > > > >> come up with an answer
>> >> >> of 80.
>> >> >> > > > >> That
>> >> >> > > can't work.
>> >> >> > > > >>
>> >> >> > > > >> If your answer is that it should be 80, and the size of
>> a
>> >> >> > > > >> pointer isn't something the frontend/IR optimizers
>> should be
>> >> >> > > > >> aware of, I'm not sure your approach makes sense; you
>> could
>> >> >> > > > >> just introduce custom load/store nodes in your target
>> which
>> >> >> > > > >> truncate the pointer, and you wouldn't need to mess with
>> the
>> >> >> > > > >> size of a pointer
>> >> >> > at all.
>> >> >> > > > > [Villmow, Micah] Yeah I see your point here. I don't deal
>> >> >> > > > > with array
>> >> >> > > > of pointers in OpenCL, so didn't think of this case.
>> >> >> > > > >
>> >> >> > > > > So, what about extending data layout to support something
>> >> like:
>> >> >> > > > > p#:size:abi:pref <- specify the size, abi and preference
>> for
>> >> >> > > > > the
>> >> >> > > > pointer of address space '#'. Default behavior is
>> >> p:size:abi:pref.
>> >> >> > > >
>> >> >> > > > That's fine.
>> >> >> > > >
>> >> >> > > > (You'll also need to deal with the fact that LLVM assumes
>> bit
>> >> >> > > > casts across address-spaces are lossless.)
>> >> >> > > >
>> >> >> > > > -Eli
>> >> >
>> >
>> >
>
>