Re: 1.76% performance loss in VRP due to inlining

[Jason Merrill <jason@redhat.com>]

On 4/30/24 12:22, Jakub Jelinek wrote:
> On Tue, Apr 30, 2024 at 03:09:51PM -0400, Jason Merrill via Gcc wrote:
>> On Fri, Apr 26, 2024 at 5:44 AM Aldy Hernandez via Gcc <gcc@gcc.gnu.org> wrote:
>>>
>>> In implementing prange (pointer ranges), I have found a 1.74% slowdown
>>> in VRP, even without any code path actually using the code.  I have
>>> tracked this down to irange::get_bitmask() being compiled differently
>>> with and without the bare bones patch.  With the patch,
>>> irange::get_bitmask() has a lot of code inlined into it, particularly
>>> get_bitmask_from_range() and consequently the wide_int_storage code.
>> ...
>>> +static irange_bitmask
>>> +get_bitmask_from_range (tree type,
>>> +                     const wide_int &min, const wide_int &max)
>> ...
>>> -irange_bitmask
>>> -irange::get_bitmask_from_range () const
>>
>> My guess is that this is the relevant change: the old function has
>> external linkage, and is therefore interposable, which inhibits
>> inlining.  The new function has internal linkage, which allows
>> inlining.
> 
> Even when a function is exported, when not compiled with -fpic/-fPIC
> if we know the function is defined in current TU, it can't be interposed,

Ah, I was misremembering the effect of the change.  Rather, it's that if 
we see that a function with internal linkage has only a single caller, 
we try harder to inline it.

Jason