[llvm-dev] linkonce expected behavior?

[Andrew Kelley via llvm-dev]

"weak" worked on linux. I'm waiting to see if tests pass for

 * MacOS: https://travis-ci.org/zig-lang/zig/jobs/292392617
 * Windows: https://ci.appveyor.com/project/andrewrk/zig-d3l86/build/1.0.478

I'll report back when they're done.


On Tue, Oct 24, 2017 at 9:49 PM, Vedant Kumar <vsk at apple.com> wrote:

>
> On Oct 24, 2017, at 6:41 PM, Andrew Kelley <superjoe30 at gmail.com> wrote:
>
> On Tue, Oct 24, 2017 at 9:27 PM, Vedant Kumar <vsk at apple.com> wrote:
>
>> Unreferenced linkonce globals are allowed to be discarded.
>>
>>
>> Is __udivmodti4 referenced?
>>
>
>
> It's referenced by a different .o file, but nothing within the module.
>
> My confusion comes from the missing direct object in the sentence.
> Referenced by a function local to the module? Referenced by any object in
> the linker job?
>
>
> Ah I see. I read this as: "Linkonce globals which aren't referenced within
> their module are allowed to be discarded."
>
> To your point here:
>
> Is there a linkage type that lets the linker merge functions of the same
>> name but does not let the optimizer delete the function?
>>
>>
> Does "weak" linkage work for you?
>
> vedant
>
>
>
>
>>
>> vedant
>>
>> On Oct 24, 2017, at 6:09 PM, Andrew Kelley via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>> http://llvm.org/docs/LangRef.html#linkage-types says:
>>
>> Globals with “linkonce” linkage are merged with other globals of the same
>> name when linkage occurs. This can be used to implement some forms of
>> inline functions, templates, or other code which must be generated in each
>> translation unit that uses it, but where the body may be overridden with a
>> more definitive definition later. Unreferenced linkonce globals are allowed
>> to be discarded. Note that linkonce linkage does not actually allow the
>> optimizer to inline the body of this function into callers because it
>> doesn’t know if this definition of the function is the definitive
>> definition within the program or whether it will be overridden by a
>> stronger definition. To enable inlining and other optimizations, use
>> “linkonce_odr” linkage.
>>
>> This makes me think that linkonce globals will not be optimized out of an
>> .o file, but they can be deleted by the linker. Here's some IR I have:
>>
>> define linkonce i128 @__udivmodti4(i128, i128, i128*) local_unnamed_addr
>> #0 !dbg !264 {
>> ....
>> }
>>
>> When I run:
>>
>> opt -O3 -S compiler_rt.ll
>>
>> It deletes the function. Is this expected behavior?
>>
>> Is there a linkage type that lets the linker merge functions of the same
>> name but does not let the optimizer delete the function?
>>
>> (let me know if providing the entire .ll file would be helpful)
>>
>> Regards,
>> Andrew Kelley
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>>
>
>
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