Re: [PATCH] bitops.h: Compile out asserts without --enable-debug

[Peter Maydell <peter.maydell@linaro.org>]

On Mon, 22 May 2023 at 13:00, BALATON Zoltan <balaton@eik.bme.hu> wrote:
> On Mon, 22 May 2023, Peter Maydell wrote:
> > Can we have some figures for performance improvements,
> > please? General QEMU policy is that asserts remain,
> > even in non-debug builds, so exceptions from that policy
> > should come with justification with figures attached.
>
> Here are some figures converting a 10MB wav file to mp3 with lame on
> AmigaOS pegasos2 which is using a lot of FPU operations (which is using
> softfloat on TCG target/ppc due to no hardfloat so it's very slow):
>
>     8.0: 1:11 0.8264x, 1:11 0x8258x
> master: 1:12 0.8117x, 1:12 0.8103x
>   patch: 1:02 0.9541x, 1:02 0.9506x

Thanks; that does seem like quite a lot of overhead.

> I've never seen these asserts firing and unlikely to depend on run time
> values so leaving them in non-debug builds seems unnecessary overkill that
> also hurts performance.

Where they don't depend on runtime values, the compiler will be
able to detect that the assert condition is always false and
won't emit any code. It's only the cases where the start or
length are variable that will be causing the slowdown.

thanks
-- PMM