[LLVMdev] Function code size estimation

[Gregory Petrosyan]

On Fri, Jun 4, 2010 at 3:47 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
> On Fri, Jun 4, 2010 at 2:46 AM, Gregory Petrosyan
> <gregory.petrosyan at gmail.com> wrote:
>> Hello,
>>
>> I am working on a pass that finds identical basic blocks and abstracts
>> them into functions, in order to reduce code size.
>>
>> To decide, whether particular basic block group is worth factoring
>> out, I want to estimate code size of some function that uses one of
>> basic blocks in question 'as is', and after factoring the basic block
>> into a new function.
>>
>> Can you please suggest a proper way to do this?
>
> You could just count the number of Instructions as an extremely rough
> estimate.  llvm/Analysis/InlineCost.h has the functions used by the
> inliner and other similar transforms to estimate the cost of a basic
> block or function, which are somewhat more accurate.

Thanks Eli,

The thing that worries me in this approach is that it is really rough,
and to make it work I need to introduce and tune some target-specific
coefficients. I thought that if there is a way to just generate real
code and measure it's size, it would be simpler as well as more
accurate.

                Gregory