[llvm-dev] How to inline function from other file in IR

[Soham Sinha via llvm-dev]

Hi all,

I solved it. I just added the keyword "__attribute__((always_inline))"
before the function signature foo. I didn't add any extern inline or static
inline or inline keyword. LLVM marks this function as an alwaysinline
function. So when I add that synthetically with my transform pass the
function is called from bar. However, the function foo is inlined when it
is turned into machine code ultimately. That's what I wanted. Thanks for
all your help.

Regards,
Soham Sinha
CS PhD Student
Boston University

On Thu, May 17, 2018, 12:47 AM Nema, Ashutosh <Ashutosh.Nema at amd.com> wrote:

> Hi Soham,
>
>
>
> “extern inline” keyword will help in this case, with this keyword compiler
> is forced to keeps the definition of the function and make it available for
> the external usage.
>
> Also it retains the “inlinehint” attribute on the function, with that lto
> inliner may make it inline.
>
>
>
> Best,
>
> Ashutosh
>
>
>
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *Mehdi
> AMINI via llvm-dev
> *Sent:* Thursday, May 17, 2018 9:42 AM
> *To:* soham1 at bu.edu
> *Cc:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] How to inline function from other file in IR
>
>
>
> Hi Soham,
>
>
>
> Are you intending to use the inline keyword in order to control the
> inlining optimization?
>
>
>
> The inline keyword is not doing this, it is changing the linkage type of
> the symbol and instruct the compiler to discard it if there is no call
> left, and also will instruct the linker to deduplicate. For instance if
> multiple file include a header that defines an inline function, this
> function could end up in multiple objects. Without the inline keyword you
> would get linker errors for duplicate symbols.
>
>
>
> So, the question become: why do you want foo to be inline in bar? If it is
> for performance then you don't need the keyword and you should rely on the
> optimizer to "do the right thing": running `opt -O2` on the resulting .ll
> file you get after llvm-link and after running your pass that adds the call
> should be enough.
>
>
>
> Best,
>
>
>
> --
>
> Mehdi
>
>
>
>
>
>
>
> Le mar. 15 mai 2018 à 16:34, Soham Sinha via llvm-dev <
> llvm-dev at lists.llvm.org> a écrit :
>
> Hello,
>
>
>
> How can I inline a function mentioned in other file?
>
>
>
> I have an inline function *foo* in C source file (a.c) which is not
> referenced in this file. I compile this file to a.ll (I notice that the
> compiled a.ll doesn't have *foo*'s definition, probably because it was
> inlined but not called anywhere)
>
> I have another C source file b.c with function *bar*; I compile this to
> b.ll
>
> I link these two files with llvm-link
>
> I have written a pass which inserts *foo *function calls to the bar
> function at some points. I want foo function calls to be *inlined*.
> However, I get  compilation error because *foo *is not found (a.ll
> doesn't have foo)
>
> If I remove the inline attribute of foo in a.c, I get the correctly
> compilation, with calls to foo inserted in bar from b.c
>
> How do I achieve this kind of inline-ing?
>
>
> Regards,
>
> Soham Sinha
>
> PhD Student, Department of Computer Science
>
> Boston University
>
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