[llvm-dev] why do undefined globals end up in .data instead of .bss?

[Friedman, Eli via llvm-dev]

On 4/24/2017 11:55 AM, Andrew Kelley wrote:
>
>
> On Mon, Apr 24, 2017 at 2:53 PM, Friedman, Eli 
> <efriedma at codeaurora.org <mailto:efriedma at codeaurora.org>> wrote:
>
>     On 4/23/2017 10:10 AM, Andrew Kelley via llvm-dev wrote:
>
>         Here is a module:
>
>         @vals = internal unnamed_addr global [20000000 x i32] undef,
>         align 4
>
>         LLVM puts the global in the .data section, and results in a
>         77MB .o file of mostly zeroes. Why does this variable not go
>         in the .bss section?
>
>
>     I think it's just an oversight; it doesn't matter for clang
>     because it never emits globals like that.  See
>     TargetLoweringObjectFile::getKindForGlobal for the relevant logic.
>
>
> I see, thanks. Would a patch be welcome which changed this behavior? 
> Or I suppose I could emit zeroinitializer instead of undef. But it 
> seems like undef is the more correct value.
>
Sure, patch welcome.

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

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