Re: 1.76% performance loss in VRP due to inlining

[Jason Merrill <jason@redhat.com>]

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.

Relatedly, I wonder if we want to build GCC with -fno-semantic-interposition?

Jason