llvm dev - Mar 2016 - LLVM 3.8 change in function argument lists?

Hi,

I am upgrading my project from 3.7 to 3.8. I find that following code
used to compile in 3.7 but doesn't in 3.8 and I can't understand why.

llvm::Function *mainFunc = ...;
auto argiter = mainFunc->arg_begin();
llvm::Value *arg1 = argiter++;
arg1->setName("obj");

But if I change the code to following it compiles:

auto argiter = mainFunc->arg_begin();
llvm::Value *arg1 = &(*argiter);
arg1->setName("obj");


As far as I can tell the first version should have worked as well. Any
pointers to why the first version is now failing to compile?

Thanks and Regards
Dibyendu

Duncan - I assume this is your ilist work?

Dibyendu: Iterators are not necessarily pointers, so you can't always
expect to convert an iterator straight to a pointer to the element type in
general.

On Mon, Mar 14, 2016 at 4:38 PM, Dibyendu Majumdar via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi,
>
> I am upgrading my project from 3.7 to 3.8. I find that following code
> used to compile in 3.7 but doesn't in 3.8 and I can't understand
why.
>
> llvm::Function *mainFunc = ...;
> auto argiter = mainFunc->arg_begin();
> llvm::Value *arg1 = argiter++;
> arg1->setName("obj");
>
> But if I change the code to following it compiles:
>
> auto argiter = mainFunc->arg_begin();
> llvm::Value *arg1 = &(*argiter);
> arg1->setName("obj");
>
>
> As far as I can tell the first version should have worked as well. Any
> pointers to why the first version is now failing to compile?
>
> Thanks and Regards
> Dibyendu
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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On 3/14/16 5:38 PM, Dibyendu Majumdar via llvm-dev
wrote:
> Hi,
>
> I am upgrading my project from 3.7 to 3.8. I find that following code
> used to compile in 3.7 but doesn't in 3.8 and I can't understand
why.
>
> llvm::Function *mainFunc = ...;
> auto argiter = mainFunc->arg_begin();
> llvm::Value *arg1 = argiter++;
> arg1->setName("obj");
>
> But if I change the code to following it compiles:
>
> auto argiter = mainFunc->arg_begin();
> llvm::Value *arg1 = &(*argiter);
> arg1->setName("obj");
>
>
> As far as I can tell the first version should have worked as well. Any
> pointers to why the first version is now failing to compile?
 From the release notes:

"ilist_iterator<T> no longer has implicit conversions to and from T*,
since ilist_iterator<T> may be pointing at the sentinel (which is 
usually not of type T at all). To convert from an iterator I to a 
pointer, use &*I; to convert from a pointer P to an iterator, use 
P->getIterator(). Alternatively, explicit conversions via 
static_cast<T>(U) are still available."

This was done to fix UB in the ilist implementation, IIRC.


Jon
>
> Thanks and Regards
> Dibyendu
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded

On 14 March 2016 at 23:42, Jonathan Roelofs <jonathan at codesourcery.com>
wrote:
>> I am upgrading my project from 3.7 to 3.8. I find that following code
>> used to compile in 3.7 but doesn't in 3.8 and I can't
understand why.
>>
>> llvm::Function *mainFunc = ...;
>> auto argiter = mainFunc->arg_begin();
>> llvm::Value *arg1 = argiter++;
>> arg1->setName("obj");
>>
>> But if I change the code to following it compiles:
>>
>> auto argiter = mainFunc->arg_begin();
>> llvm::Value *arg1 = &(*argiter);
>> arg1->setName("obj");
>>
>>
> From the release notes:
>
> "ilist_iterator<T> no longer has implicit conversions to and
from T*, since
> ilist_iterator<T> may be pointing at the sentinel (which is usually
not of
> type T at all). To convert from an iterator I to a pointer, use &*I; to
> convert from a pointer P to an iterator, use P->getIterator().
> Alternatively, explicit conversions via static_cast<T>(U) are still
> available."
>
> This was done to fix UB in the ilist implementation, IIRC.
>
Ok thanks.

Regards
Dibyendu

> On 2016-Mar-14, at 16:41, David Blaikie <dblaikie at gmail.com>
wrote:
> 
> Duncan - I assume this is your ilist work?
Yes.  Looks like the rest has been answered by others!
> Dibyendu: Iterators are not necessarily pointers, so you can't always
expect to convert an iterator straight to a pointer to the element type in
general.
> 
> On Mon, Mar 14, 2016 at 4:38 PM, Dibyendu Majumdar via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hi,
> 
> I am upgrading my project from 3.7 to 3.8. I find that following code
> used to compile in 3.7 but doesn't in 3.8 and I can't understand
why.
> 
> llvm::Function *mainFunc = ...;
> auto argiter = mainFunc->arg_begin();
> llvm::Value *arg1 = argiter++;
> arg1->setName("obj");
> 
> But if I change the code to following it compiles:
> 
> auto argiter = mainFunc->arg_begin();
> llvm::Value *arg1 = &(*argiter);
> arg1->setName("obj");
> 
> 
> As far as I can tell the first version should have worked as well. Any
> pointers to why the first version is now failing to compile?
> 
> Thanks and Regards
> Dibyendu
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>