[LLVMdev] LTO type uniquing: ODR assertion failure

[Manman Ren]

On Mon, Jul 21, 2014 at 3:41 PM, David Blaikie <dblaikie at gmail.com> wrote:

> On Mon, Jul 21, 2014 at 3:35 PM, Manman Ren <manman.ren at gmail.com> wrote:
> >
> >
> >
> > On Mon, Jul 21, 2014 at 1:14 PM, David Blaikie <dblaikie at gmail.com>
> wrote:
> >>
> >> On Mon, Jul 21, 2014 at 10:39 AM, Manman Ren <manman.ren at gmail.com>
> wrote:
> >> >
> >> >
> >> >
> >> > On Mon, Jul 14, 2014 at 11:32 AM, Manman Ren <manman.ren at gmail.com>
> >> > wrote:
> >> >>
> >> >>
> >> >> We still have access to types via MDNodes directly and the assertion
> >> >> that
> >> >> assumes all accesses to DITypes are accessing the resolved DIType
> will
> >> >> fire
> >> >>
> >> >> i.e assert(Ty == resolve(Ty.getRef()))
> >> >>
> >> >> One example is the access to DIType via DIArray in SubroutineType. If
> >> >> all
> >> >> elements in the type array are DITypes we can create a DITypeArray
> and
> >> >> use
> >> >> that for SubroutineType's type array instead. But we currently have
> >> >> unspecified parameter in the type array and it is not a DIType.
> >> >
> >> >
> >> > I am going to work on a patch that adds DITypeArray (each element will
> >> > be
> >> > DITypeRef, SubroutineType's type array will be DITypeArray) and adds
> >> > DITrivialType that extends from DIType (unspecified parameter will be
> >> > DITrivialType).
> >> > If you  have opinions against it, please let me know,
> >>
> >> We haven't bothered using typed arrays in DebugInfo yet (as you say,
> >> we just have DIArray) so I have two thoughts
> >>
> >> 1) why does this one case need fixing/changing? Is it because we have
> >> things that aren't DIDescriptors inside the DIArray? (the strings that
> >> refer to types). Given how loosely typed DIDescriptor is (it doesn't
> >> check that it's a valid DIDescriptor) I assume this doesn't actually
> >> cause a problem, though it's certainly not nice. So we could just
> >> leave it as-is, pass DIArray's element to "resolve" (it'd implicitly
> >> convert the DIDescriptor back to a raw MDNode*), then perhaps we'd
> >> need to make DITypeRef's ctor public so it could be used here. Not
> >> suggesting that's ideal, though.
> >
> >
> > I should have provided an example to help understanding the issue :)
> >
> > When processing the following type node, we throw an assertion failure
> > assert(Ty == resolve(Ty.getRef()))
> > !{i32 786436, metadata <badref>, null, metadata !"SpuPacketType", i32
> 102,
> > i64 32, i64 32, i32 0, i32 0, null, metadata <badref>, i32 0, null, null,
> > metadata !"_ZTS13SpuPacketType"} ; [ DW_TAG_enumeration_type ]
> > [SpuPacketType] [line 102, size 32, align 32, offset 0] [def] [from ]
> >
> > There are two type nodes with the same identifier:
> > !473 = metadata !{i32 786436, metadata !474, null, metadata
> > !"SpuPacketType", i32 102, i64 32, i64 32, i32 0, i32 0, null, metadata
> > !475, i32 0, null, null, metadata !"_ZTS13SpuPacketType"} ; [
> > DW_TAG_enumeration_type ] [SpuPacketType] [line 102, size 32, align 32,
> > offset 0] [def] [from ]
> > !6695 = metadata !{i32 786436, metadata !6696, null, metadata
> > !"SpuPacketType", i32 102, i64 32, i64 32, i32 0, i32 0, null, metadata
> > !475, i32 0, null, null, metadata !"_ZTS13SpuPacketType"} ; [
> > DW_TAG_enumeration_type ] [SpuPacketType] [line 102, size 32, align 32,
> > offset 0] [def] [from ]
> >
> > The only difference between these two is the file node
> > !474 = metadata !{metadata
> >
> !"/Users/manmanren/swb/rdar_17628609/AppleSPUFirmware-71/SPU/SPUPacket.h",
> > metadata !"/Users/manmanren/swb/rdar_17628609/AppleSPUFirmware-71"}
> > !6696 = metadata !{metadata
> >
> !"/Users/manmanren/swb/rdar_17628609/AppleSPUFirmware-71/SPU/../SPU/SPUPacket.h",
> > metadata !"/Users/manmanren/swb/rdar_17628609/AppleSPUFirmware-71"}
> >
> > We have direct access to 473 via 580's type array.
> > !580 = metadata !{i32 786453, i32 0, null, metadata !"", i32 0, i64 0,
> i64
> > 0, i64 0, i32 0, null, metadata !581, i32 0, null, null, null} ; [
> > DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
> > !581 = metadata !{metadata !124, metadata !575, metadata !473, metadata
> > !582, metadata !212, metadata !128, metadata !584}
> >
> > MDNode 473 will be resolved to MDNode 6695 and the assertion "assert(Ty
> ==
> > resolve(Ty.getRef()))" will fire.
> >
> > -------------------------------------------------
> > To fix the problem, we need to remove the direct access to MDNode 473 by
> > replacing MDNode 581 from
> > metadata !{metadata !124, metadata !575, metadata !473, metadata !582,
> > metadata !212, metadata !128, metadata !584}
> > to
> > metadata !{metadata !124, metadata !575, metadata !"_ZTS13SpuPacketType",
> > metadata !582, metadata !212, metadata !128, metadata !584}
> >
> > And treat the field {metadata !"_ZTS13SpuPacketType"} as DITypeRef.
> >
> > -------------------------------------------------
> > If we have DIDescriptorRef and all elements currently inside DIArray are
> > DIDescirptors, we can make DIArray an array of DIDescriptorRef.
> > I don't think it is a good idea to add DIDescriptorRef (it makes our
> types
> > loose) and am not sure about the 2nd condition.
> >
> > So I proposed to add DITypeArray (or DITypedArray<DITypeRef> as David
> > suggested, where all elements are DITypeRef),
> > DICompositeType::getTypeArray() will return DITypeArray and
> > DITypeArray::getElement(unsigned) will return DITypeRef.
> >
> > This is actually more complicated than I thought, not all
> DICompositeType's
> > getTypeArray() can return an array of DITypeRefs. For example,
> > getTypeArray() of ArrayType and VectorType can not return an array of
> > DITypeRefs.
>
> Why can't they?
>

For ArrayType, we create it like this:
  SmallVector<llvm::Value *, 8> Subscripts;
...
Subscripts.push_back(DBuilder.getOrCreateSubrange(0, Count));
...
  llvm::DIArray SubscriptArray = DBuilder.getOrCreateArray(Subscripts);

The elements of getTypeArray() are DISubranges, even though the function is
called getTypeArray :)


>
> > We can fix that by extending DICompositeType to DISubroutineType and only
> > DISubroutineType::getTypeArray() will return DITypeArray.
> > Even for SubroutineType, elements of the type array can be unspecified
> > parameters which can't be DITypeRefs.
>
> Again - I'm just missing why this is the case. DITypeRefs can be
> direct references to types (such as file-internal C++ user defined
> types) so there's always a safe fallback, isn't there?
>

If a SubroutineType's getTypeArray() contains unspecified parameter (which
is a DIDescriptor, not a DIType), we can't say
DISubroutineType::getTypeArray() will return DITypeArray,
since we assume DITypeArray (or DITypedArray<DITypeRef>) have all elements
being DITypeRefs.

Thanks,
Manman

>
> > That is why I was thinking about
> > making unspecified parameters trivial DITypes.
> >
> > Thanks a lot,
> > Manman
> >
> >>
> >>
> >> 2) If we're going to fix DIArray apparent type safety (it's not safe -
> >> just convenient), perhaps we could just template it? (to avoid churn,
> >> we could leave DIArray as a typedef of DITypedArray<DIDescriptor> for
> >> example, and then have DITypedArray<DITypeRef> which is your
> >> DITypeArray (again, provided via typedef)). It's so small though, that
> >> I'm not too fussed if we write it out again as you've proposed.
> >>
> >> - David
> >>
> >> >
> >> > Thanks,
> >> > Manman
> >> >
> >> >>
> >> >> What are your thoughts? Suggestions are welcome.
> >> >>
> >> >> Is it a good idea to canonicalize file names (i.e dA/B.h should be
> >> >> equivalent to dA/../dA/B.h)? This will reduce the chance of having
> two
> >> >> DITypes that should be equivalent with equivalent file names.
> >> >>
> >> >> Thanks,
> >> >> Manman
> >> >
> >> >
> >
> >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20140721/48a35527/attachment.html>