llvm dev - May 2018 - How to inline function from other file in IR

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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It sounds like you want to compile with LTO (-flto) after removing the
'inline' from 'foo'.  That should enable the
cross-compilation-unit inlining you want.
--paulr

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Soham
Sinha via llvm-dev
Sent: Tuesday, May 15, 2018 7:33 PM
To: via llvm-dev
Subject: [llvm-dev] How to inline function from other file in IR

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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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
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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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<mailto: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
_______________________________________________
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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