[PATCH] Implement throw in conditional operator

[Marius Wachtler]

Sorry for all the spam...
I attached the wrong patch file.



On Wed, Jun 11, 2014 at 11:16 PM, Marius Wachtler <undingen at gmail.com>
wrote:

> Thanks for your expertise.
> Attached you can find an updated patch where I removed the const and made
> the FileCheck a little bit more specific.
>
>
>
> On Wed, Jun 11, 2014 at 10:55 PM, Richard Smith <richard at metafoo.co.uk>
> wrote:
>
>> On Wed, Jun 11, 2014 at 1:25 PM, Marius Wachtler <undingen at gmail.com>
>> wrote:
>>
>>> Hi
>>>
>>> I added a testcase for the function you mention but I also added const
>>> to the return type because otherwise gcc won't compile it ("error: invalid
>>> initialization of non-const reference of type ‘int&’ from an rvalue of type
>>> ‘int’") - clang compiles both.
>>>
>>
>> GCC doesn't implement one of the relevant DRs; you don't need to make the
>> testcase work with it.
>>
>> The generated code from clang for the function looks correct and works as
>>> I would expect it.
>>> Compiling it with g++ 4.8.2 and -O2 will instead produce and object
>>> which will return an address to a temporary in the function and not a
>>> reference to the global val.
>>>
>>> I'm not sure if clangs behavior is correct or if it should also only
>>> accept a const reference? If the error is somewhere else I would appreciate
>>> some guidance to where to look around and what the expected behavior is.
>>>
>>
>> See http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1550;
>> Clang's behavior is right, this is just a bug with IR generation.
>>
>> The C++11 non final standard I have says (5.16-2):
>>> "If either the second or the third operand has type (possibly
>>> cv-qualified) void, then the lvalue-to-rvalue (4.1), array-to-pointer (4.2),
>>> and function-to-pointer (4.3) standard conversions are performed on the
>>> second and third operands, and one of the following shall hold:
>>> — The second or the third operand (but not both) is a throw-expression
>>> (15.1); the result is of the type
>>> of the other and is a prvalue.
>>> — Both the second and the third operands have type void; the result is
>>> of type void and is a prvalue. [ Note: This includes the case where both
>>> operands are throw-expressions. — end note ]
>>> "
>>> So this means gcc is correct?
>>>
>>> Thank you very much
>>> - Marius
>>>
>>>
>>>
>>>
>>>
>>> On Wed, Jun 11, 2014 at 1:05 AM, Richard Smith <richard at metafoo.co.uk>
>>> wrote:
>>>
>>>> Please also include a test that the produced lvalue actually has the
>>>> right value. Something like:
>>>>
>>>> int &test7(bool cond) {
>>>>   return cond ? throw 1 : val;
>>>> }
>>>>
>>>> ... and check that the value returned is @_Z3val
>>>>
>>>> On Tue, Jun 10, 2014 at 3:01 PM, Marius Wachtler <undingen at gmail.com>
>>>> wrote:
>>>>
>>>>> Hi
>>>>> Attached you can find an updates patch.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Jun 10, 2014 at 11:50 PM, David Majnemer <
>>>>> david.majnemer at gmail.com> wrote:
>>>>>
>>>>>> +
>>>>>>> +  case Expr::CXXThrowExprClass: {
>>>>>>> +    const auto* throwExpr = cast<CXXThrowExpr>(E);
>>>>>>>
>>>>>>
>>>>>> Please stick the star on the RHS. Also, it is customary in LLVM and
>>>>>> clang to spell it like "ThrowExpr"
>>>>>>
>>>>>>
>>>>>>> +    EmitCXXThrowExpr(throwExpr);
>>>>>>> +    const QualType subExprType = throwExpr->getSubExpr()->getType();
>>>>>>>
>>>>>>
>>>>>> Likewise for "subExprType"
>>>>>>
>>>>>> +    llvm::Type *Ty =
>>>>>>> llvm::PointerType::getUnqual(ConvertType(subExprType));
>>>>>>> +    return MakeAddrLValue(llvm::UndefValue::get(Ty), subExprType);
>>>>>>>    }
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Tue, Jun 10, 2014 at 5:19 PM, Marius Wachtler <undingen at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> Hello
>>>>>>>
>>>>>>> Attached you can find my first clang patch which should implement
>>>>>>> "cond ? throw 1 : val".
>>>>>>>
>>>>>>> Without this patch I get: "cannot compile this l-value expression
>>>>>>> yet"
>>>>>>>
>>>>>>> As this is my first time looking under the hood of clang I'm not
>>>>>>> sure if this is the right approach. I'm Looking forward to your feedback.
>>>>>>>
>>>>>>> - Marius Wachtler
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> cfe-commits mailing list
>>>>>>> cfe-commits at cs.uiuc.edu
>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> cfe-commits mailing list
>>>>> cfe-commits at cs.uiuc.edu
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>>>>>
>>>>>
>>>>
>>>
>>
>
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