[llvm-dev] Why is printing an Instruction so slow?

[mats petersson via llvm-dev]

Using `llvm::outs()` will only be noticeably faster if `std::endl;` is
replaced with `'\n'` or similar, since `std::endl;` will cause a flush as
well - it may be little better, but for buffering to work well, you wan't a
few thousand characters in the buffer, not just a few dozen.

--
Mats

On 5 October 2015 at 17:05, don hinton via llvm-dev <llvm-dev at lists.llvm.org
> wrote:

> Hi Steve:
>
> llvm::errs() is unbuffered, so that might explain it.  Could you try
> llvm::outs() instead and see if that helps.
>
> hth...
> don
>
> On Mon, Oct 5, 2015 at 11:17 AM, Stephen Thomas via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi all,
>>
>> When writing my custom passes, I often emit log messages to llvm::errs()
>> like so:
>>
>> llvm::errs() << "Could not handle instruction: " << *Inst << std::endl;
>>
>> where Inst is a pointer to an Instruction.
>>
>> I've profiled my code and found that this way of printing an Instruction
>> takes a very long time: indeed, it is the bottleneck of my pass.
>>
>> Of course, I could always switch these log messages off for production
>> runs, but during development and debugging, I'd like to have them on to
>> make debugging much easier.
>>
>> Is there a faster way to print an Instruction?
>>
>> Thanks,
>> Steve
>>
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>> llvm-dev at lists.llvm.org
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>>
>>
>
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