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

[Villmow, Micah]

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?

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
> >> >
> >
> >