[llvm-dev] LLVM 3.9 RC2's SCCP pass removing calls to external functions?!

[Daniel Berlin via llvm-dev]

(though it's still illegal to remove it in this particular case).

I'm just saying, just because you don't make a function read-only or
read-none, doesn't mean clang/llvm won't infer the attribute.

Here, it's illegal because you don't have the definition.

The function is also may-throw.
So even if it was readnone/readonly, we could not remove the call.



On Wed, Aug 24, 2016 at 8:57 AM, Daniel Berlin <dberlin at dberlin.org> wrote:

> Actually, this is false.
> It will infer the attribute :)
>
>
>
> On Wed, Aug 24, 2016 at 5:47 AM, Renato Golin via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> On 24 August 2016 at 11:45, Alexandre Isoard <alexandre.isoard at gmail.com>
>> wrote:
>> > However, he also stated that in the case the functions returns void it
>> is
>> > not removed, which suggest there is something fishier going on.
>>
>> Looking back at the example (and LangRef, for function attributes),
>> looks like it's not legal to remove because the function does *not*
>> have "readnone" or "readonly", so LLVM can't prove it side-effect
>> free.
>>
>> Sanjoy's fix is probably on the right track.
>>
>> --renato
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>
>
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