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

[Eli Friedman]

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
>> >
>
>