r218287 - Don't use comdats for initializers on platforms that don't support it

[Reid Kleckner]

Should be fixed in r218337.

On Tue, Sep 23, 2014 at 3:01 PM, Reid Kleckner <rnk at google.com> wrote:

> Yes, it's globalopt. Here's the reduction:
>
> $ cat t.ll
> $comdat_global = comdat any
> @comdat_global = weak_odr global i8 0, comdat $comdat_global
> @simple_global = internal global i8 0
> @llvm.global_ctors = appending global [2 x { i32, void ()*, i8* }] [
>     { i32, void ()*, i8* } { i32 65535, void ()* @init_comdat_global, i8*
> @comdat_global },
>     { i32, void ()*, i8* } { i32 65535, void ()* @init_simple_global, i8*
> null }
> ]
> define void @init_comdat_global() {
>   store i8 42, i8* @comdat_global
>   ret void
> }
> define void @init_simple_global() comdat $comdat_global {
>   store i8 42, i8* @simple_global
>   ret void
> }
>
> $ opt t.ll -globalopt -S -o -
> ; ModuleID = 't.ll'
>
> $comdat_global = comdat any
>
> @comdat_global = weak_odr global i8 0, comdat $comdat_global
> @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32,
> void ()*, i8* } { i32 65535, void ()* @init_comdat_global, i8* null }]
>
> define void @init_comdat_global() {
>   store i8 42, i8* @comdat_global
>   ret void
> }
>
> define void @init_simple_global() comdat $comdat_global {
>   ret void
> }
>
> Note the missing comdat field in global_ctors.
>
> On Tue, Sep 23, 2014 at 11:52 AM, Reid Kleckner <rnk at google.com> wrote:
>
>> I reverted this. It needs more investigation. With optimizations enabled,
>> I'm seeing a comdat group that looks like:
>>
>> COMDAT group section [    2] `.group' [_ZN...kNameE] contains 4 sections:
>>    [Index]    Name
>>    [   43]   .text.startup
>>    [   76]   .bss._ZN...kNameE
>>    [   83]   .bss._ZGV..kNameE
>>    [   44]   .rela.text.startup
>>
>> Note that there is no .ctors section in the group. Maybe -globalopt fired?
>>
>> On Mon, Sep 22, 2014 at 9:39 PM, Anton Korobeynikov <
>> anton at korobeynikov.info> wrote:
>>
>>> Yeah, the only difference between .ctors and .init_array is the order
>>> which the initializers are emitted in the section in.
>>>
>>> On Tue, Sep 23, 2014 at 4:58 AM, Rafael Avila de Espindola
>>> <rafael.espindola at gmail.com> wrote:
>>> >
>>> >
>>> > Sent from my iPhone
>>> >
>>> > On Sep 22, 2014, at 20:55, Reid Kleckner <rnk at google.com> wrote:
>>> >
>>> > On Mon, Sep 22, 2014 at 5:32 PM, Rafael Avila de Espindola
>>> > <rafael.espindola at gmail.com> wrote:
>>> >>
>>> >>
>>> >> > URL: http://llvm.org/viewvc/llvm-project?rev=218287&view=rev
>>> >> > Log:
>>> >> > Don't use comdats for initializers on platforms that don't support
>>> it
>>> >> >
>>> >> > In particular, pre-.init_array ELF uses the .ctors section
>>> mechanism.
>>> >> > MinGW COFF also uses .ctors, now that I think about it.
>>> >>
>>> >> Why doesn't it work with .ctors? It is just a list of pointers like
>>> >> .init_array.
>>> >
>>> >
>>> > I didn't think it was implemented. Are you saying it's possible and
>>> should
>>> > be easy, or that it should already work? We're having issues with my
>>> > favorite gold error, "relocation refers to discarded section".
>>> >
>>> >
>>> > I though I had implemented comdat in both .ctors and .init_array in
>>> the same
>>> > commit in LLVM.
>>> >
>>> > Would you mind reporting a bug with a testcase that used to fail? I
>>> will
>>> > take a look as soon as I get back.
>>> >
>>> > Thanks,
>>> > Rafael
>>> >
>>> > _______________________________________________
>>> > cfe-commits mailing list
>>> > cfe-commits at cs.uiuc.edu
>>> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>>> >
>>>
>>>
>>>
>>> --
>>> With best regards, Anton Korobeynikov
>>> Faculty of Mathematics and Mechanics, Saint Petersburg State University
>>>
>>
>>
>
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