[LLVMdev] Running an IR pass after all IR passes

[Will Dietz]

FWIW you can pass flags to LTO by escaping it with the following when
invoking clang:

-Wl,--plugin-opt,-my-pass-option

Or at least you used to be able to.  That said, environment variables
can be a good fallback
for stubborn build systems that do things like strip unrecognized linker flags.

~Will

On Sun, Mar 30, 2014 at 12:47 PM, Rahman Lavaee
<rlavaee at cs.rochester.edu> wrote:
> Thank you very much John.
> With an environment variable I need to take some special care, but it looks
> like the only way to go.
>
>
> On Sun, Mar 30, 2014 at 11:07 AM, John Criswell <criswell at illinois.edu>
> wrote:
>>
>> Dear Rahman,
>>
>> I think your best option is to modify the code in libLTO so that it runs
>> your pass when you want it to run.  I believe the file you want to modify is
>> LTOCodeGenerator.cpp.
>>
>> This does mean that passing options to your pass will be difficult or
>> impossible.  However, you can either hard-code the options you need or read
>> them from an environment variable if there is no easy way to pass options to
>> the libLTO.
>>
>> If you want to go the llc route, then you'll need to modify the llc code
>> so that it runs your pass instead of opt; sadly, I don't know off-hand where
>> the code is that you would need to modify (it is either in llc or in some
>> LLVM library somewhere).  The only reason I discourage the llc route is
>> because it is difficult to get whole-program bitcode files for large
>> programs (e.g., Apache).
>>
>> Regards,
>>
>> John Criswell
>>
>>
>> On 3/29/14, 12:47 AM, Rahman Lavaee wrote:
>>
>> Hi,
>> I am finding it difficult to see how I can run an IR instrumentation pass
>> after "all" IR passes.
>> I previously used opt to run my pass after linking all the llvm bitcode
>> files and then ran llc.
>> I found out that llc runs some other Function passes which depend on the
>> target.
>> For example, tail calls are only supported in x86 under some
>> circumstances.
>>
>> Then I tried lto and link time optimization. But I found it difficult to
>> specify a flag option for my instrumentation pass.
>>
>> Is there any way in llvm to run an IR pass after all IR passes?
>>
>>
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>
>
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