llvm dev - Jul 2011 - [LLVMdev] Lack of use of LLVMContextImpl::NamedStructTypes

Several people on this list have reported issues with the linker regarding a 
named StructType instance with the same name in two different modules
being resolved into two StructTypes with different names due to StructType::
setName(…) collision behavior. Looking at BitcodeReader::ParseTypeTableBody(…),
I don't see use of LLVMContextImpl::NamedStructTypes or of
Module::getTypeByName(…).
Nor do I see this use anywhere else in BitcodeReader's implementation (.cpp
file).

Doesn't the context's NamedStructTypes (checking for a previously
created StructType
with the same name), have to be used before setName(…) is called so that a new
structure
is not erroneously created?

My apologies if this is noise.

Garrison

On Mon, Jul 25, 2011 at 10:50 AM, Garrison Venn <gvenn.cfe.dev at
gmail.com> wrote:
> Several people on this list have reported issues with the linker regarding
a
> named StructType instance with the same name in two different modules
> being resolved into two StructTypes with different names due to
StructType::
> setName(…) collision behavior. Looking at
BitcodeReader::ParseTypeTableBody(…),
> I don't see use of LLVMContextImpl::NamedStructTypes or of
Module::getTypeByName(…).
> Nor do I see this use anywhere else in BitcodeReader's implementation
(.cpp file).
The BitcodeReader has nothing to do with the issue in question; the
relevant code is in lib/Linker.

-Eli

Thanks for the clarification Eli.

In looking at a stack trace from:

Linker::LinkInFiles(…) to:
BitcodeReader::ParseTypeTableBody()

it seemed that not using NamedStructTypes would cause an issue.

Thanks again

Garrison

On Jul 25, 2011, at 14:20, Eli Friedman wrote:
> On Mon, Jul 25, 2011 at 10:50 AM, Garrison Venn <gvenn.cfe.dev at
gmail.com> wrote:
>> Several people on this list have reported issues with the linker
regarding a
>> named StructType instance with the same name in two different modules
>> being resolved into two StructTypes with different names due to
StructType::
>> setName(…) collision behavior. Looking at
BitcodeReader::ParseTypeTableBody(…),
>> I don't see use of LLVMContextImpl::NamedStructTypes or of
Module::getTypeByName(…).
>> Nor do I see this use anywhere else in BitcodeReader's
implementation (.cpp file).
> 
> The BitcodeReader has nothing to do with the issue in question; the
> relevant code is in lib/Linker.
> 
> -Eli

On Jul 25, 2011, at 10:50 AM, Garrison Venn wrote:
> Several people on this list have reported issues with the linker regarding
a
> named StructType instance with the same name in two different modules
> being resolved into two StructTypes with different names due to
StructType::
> setName(…) collision behavior. Looking at
BitcodeReader::ParseTypeTableBody(…),
> I don't see use of LLVMContextImpl::NamedStructTypes or of
Module::getTypeByName(…).
> Nor do I see this use anywhere else in BitcodeReader's implementation
(.cpp file).
> 
> Doesn't the context's NamedStructTypes (checking for a previously
created StructType
> with the same name), have to be used before setName(…) is called so that a
new structure
> is not erroneously created?
Hi Garrison,

Do the other two threads answer the question here?

-Chris

Thanks for the response Chris,

On Jul 26, 2011, at 0:44, Chris Lattner wrote:
> 
> On Jul 25, 2011, at 10:50 AM, Garrison Venn wrote:
> 
>> Several people on this list have reported issues with the linker
regarding a
>> named StructType instance with the same name in two different modules
>> being resolved into two StructTypes with different names due to
StructType::
>> setName(…) collision behavior. Looking at
BitcodeReader::ParseTypeTableBody(…),
>> I don't see use of LLVMContextImpl::NamedStructTypes or of
Module::getTypeByName(…).
>> Nor do I see this use anywhere else in BitcodeReader's
implementation (.cpp file).
>> 
>> Doesn't the context's NamedStructTypes (checking for a
previously created StructType
>> with the same name), have to be used before setName(…) is called so
that a new structure
>> is not erroneously created?
> 
> Hi Garrison,
> 
> Do the other two threads answer the question here?
> 
> -Chris
Yes I believe the other threads concerning the same issue answer why the system,
because
of the lack of type linkage, is lenient in "unioning" types. What
I'm still uncomfortable with is, I
don't understand under what conditions the system should union two opaque
types with the
same name and def. The above method BitcodeReader::ParseTypeTableBody, never
seems to do
this, and therefore my reading of Linker::LinkInFiles won't do it either for
say two bitcode files
accessing/realizing the same named StructType. On the other hand when hand
coding two
modules using in memory IR, I have a choice in either checking with
NamedStructTypes to to force
two equivalently named struct types to resolve to the same struct type with the
same name, or
ignoring the issue, and just have each module create two different struct types
(via StructType
name collision behavior), with different names but with the same definition.
Does the name
matter given that the definitions are the same?

Regardless unless you feel there is some pedagogic value to the list, you can
ignore my lack of
understanding here because I'm now pretty sure I'm just creating noise
that will be resolved
for me by writing tests; not just by looking at code where I'm am probably
missing something
anyway. If there is a more concrete question I can ask, when looking at my
tests, I'll ask again
then.

Thanks again

Garrison