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From: | Stefan Monnier |
Subject: | Re: Time to merge scratch/correct-warning-pos into master, perhaps? |
Date: | Tue, 25 Jan 2022 08:27:55 -0500 |
User-agent: | Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) |
> The C level EQ operation takes twice as long when the operands do not > match, and the same time as before when they do match. I highly doubt reality is that simple because CPU performance is a lot more complex than just counting instructions. > When one of the operands is a literal nil, there is no increase in > execution time. That's an oversimplification as well: it's only when we use the `NILP` macro that the extra cost is avoided. Any use of `EQ` is still slowed down when it happens to receive a nil as one of the arguments. I do find the slowdowns discussed here rather worrisome. I thought the original agreement was that it was OK to install this change if the slowdown could be brought down to about 1% or below (for the non-compilation case). More importantly, I wonder how slowing down EQ by a factor of 2 can end up costing 10% of runtime when running the test suite. I think this deserves investigation. Stefan
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