[llvm-dev] Running DCE after my pass

[Tehila Mayzels via llvm-dev]

I understand. Thanks a lot!

 

From: Jingyue Wu [mailto:jingyue at google.com] 
Sent: Tuesday, December 29, 2015 8:29 PM
To: Tehila Mayzels
Cc: llvm-dev
Subject: Re: [llvm-dev] Running DCE after my pass

 

Hi Tehila, 

 

LLVM should not unconditionally remove such a function call because @foo may have side effects. IIRC, if you mark @foo as "readonly" (http://llvm.org/docs/LangRef.html#function-attributes), then DCE should be able to remove the call. 

 

On Tue, Dec 29, 2015 at 8:55 AM, Tehila Mayzels via llvm-dev <llvm-dev at lists.llvm.org> wrote:

Hi,

 

I wrote an IR pass and it adds some instructions that are not used.

For example:

 

%1 = call i64 @foo()

 

When %1 is not used at all.

 

I thought that running DCE (-dce) or DIE (-die) after my pass will remove such instructions, but it didn't.

 

Why? And is there a way to do that?

 

Thanks,

Tehila.


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