<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jun 24, 2015 at 3:28 PM, Duncan P. N. Exon Smith <span dir="ltr"><<a href="mailto:dexonsmith@apple.com" target="_blank">dexonsmith@apple.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5"><br>
> On 2015 Jun 20, at 01:39, Justin Bogner <<a href="mailto:mail@justinbogner.com">mail@justinbogner.com</a>> wrote:<br>
><br>
> David Blaikie <<a href="mailto:dblaikie@gmail.com">dblaikie@gmail.com</a>> writes:<br>
>> On Fri, Jun 19, 2015 at 11:52 PM, Justin Bogner <<a href="mailto:mail@justinbogner.com">mail@justinbogner.com</a>> wrote:<br>
>>> David Blaikie <<a href="mailto:dblaikie@gmail.com">dblaikie@gmail.com</a>> writes:<br>
>>>> On Fri, Jun 19, 2015 at 11:24 PM, Justin Bogner <<a href="mailto:mail@justinbogner.com">mail@justinbogner.com</a> wrote:<br>
>>>>> - while (!DeadInsts.empty())<br>
>>>>> - if (Instruction *Inst =<br>
>>>>> - dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))<br>
>>>>> + while (!DeadInsts.empty()) {<br>
>>>>> + Value *V = static_cast<Value *>(DeadInsts.pop_back_val());<br>
>>>>> + if (Instruction *Inst = dyn_cast_or_null<Instruction>(V))<br>
>>>>><br>
>>>> Hmm - I think there's some fancy machinery in the llvm cast stuff to allow<br>
>>>> us to map through from different types (so we could say that casting a<br>
>>>> WeakVH retrieves the Value* first), maybe... (so you could just<br>
>>>> dyn_cast_or_null<Value*>(DeadInsts.pop_back_val()) directly)<br>
>>><br>
>>> I don't really understand what you're going for here - we need to cast<br>
>>> twice. We have a WeakVH, which we can get a Value* out of, then we<br>
>>> dyn_cast_or_null that to an Instruction*. There's no need to dyn_cast to<br>
>>> a Value* (we want the conversion operator), and obviously WeakVH can't<br>
>>> be cast to Instruction* directly, since they're unrelated types.<br>
>><br>
>> What I mean is we have a way of making them related, through a template<br>
>> called simplify_type. Here's the version for QualType to allow QualTypes to<br>
>> be casted to specific clang::Types: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__clang.llvm.org_doxygen_&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=Kh_2JCkEJHkynRSU-PaKuEN9UFZmGVy64wsQcwxgDAM&s=qV6JpWZp7grHCmvdlEzWU9WYKTJUfjRQ7VxDSV3yOrI&e=" rel="noreferrer" target="_blank">http://clang.llvm.org/doxygen/</a><br>
>> structllvm_1_1simplify__type_3_01_1_1clang_1_1QualType_01_4.html<br>
>><br>
>> I think it /might/ work here, but I don't know/recall the specifics -<br>
>> perhaps it doesn't fit here for some reason.<br>
><br>
> Ah, I see what you mean. Interestingly, WeakVH already has a<br>
> specialization of simplify_type, so you would expect this to work:<br>
><br>
> if (Instruction *Inst =<br>
> dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))<br>
><br>
> but it doesn't - the rvalue gets type `const llvm::Instruction *` so we<br>
> get an error for trying to remove the const without a cast. On the other<br>
> hand, this does work:<br>
><br>
> WeakVH WVH = DeadInsts.pop_back_val();<br>
> if (Instruction *Inst = dyn_cast_or_null<Instruction>(WVH))<br>
><br>
> So for whatever reason the template specialization chooses the const<br>
> version (even though the non-const version is also viable) when we give<br>
> it an rvalue. I guess this is a bug or limitation in simplify_type.<br>
<br>
</div></div>Just needed another template specialization for `const WeakVH`. I added<br>
one (and used it in IndVarSimplify) in r240599.<br></blockquote><div><br>Is this a bug in the way the traits work - such that it should work for const and non-const? Something we could fix more generally? (or should we make it so that a specialization for simplify_type of const T also works for T? So shallow-const handles like this only need one specialization)<br> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<span class="im HOEnZb"><br>
> As it stands, I find the static_cast clearer than the implicit<br>
> conversion, especially since the obvious transformation of getting rid<br>
> of the temp variable doesn't work with the implicit conversion, so I'm<br>
> going to leave this as is.<br>
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