* Denys Vlasenko <dvlas...@redhat.com> wrote:
> After TESTs, use logically correct JZ mnemonic instead of JE
> (this doesn't change code).
>
> Tidy up CMPW insns:
>
> Modern CPUs are not good with 16-bit operations.
> The instructions with 16-bit immediates are especially bad,
> on many CPUs they cause length changing prefix stall
> in the decoders, costing ~6 cycles to recover.
>
> Replace CMPWs with CMPLs.
> Of these, for form with 8-bit sign-extended immediates
> it is a win because they are smaller now
> (no 0x66 prefix anymore);
> ones with 16-bit immediates are faster.
This patch does JE->JZ transitions, but it also does CMPW instruction
tweaking - which was buggy as Brian (miraculously!) noticed.
This isn't the first such incident, and I made this point about three
times already in the past, but it appears I've not made it loud
enough: which part of 'do not put two unrelated changes into the same
patch' did you not understand??
We _DO NOT PUT_ multiple, unrelated changes to assembly files into a
single patch! And we _especially_ don't mix them up under a
meaningless, repetitive, misleading 'tidy up instructions' title!
Full stop.
The titles of the two patches should have been something like:
x86/asm/entry/32: Convert JNE to JNZ mnemonics, to improve readability
x86/asm/entry/32: Optimize CMPW to CMPL instructions, to make use of automatic
zero-extend
We were lucky that Brian was alert enough to have read through a
misleadingly titled, seemingly harmless patch and noticed the bug in
your patch, but heck you made it hard!!!
And no, it's not a problem if you create a dozen trivial looking
patches and have to wait a bit more for them to trickle into the
maintainer tree: asm patches are seldom trivial, and even if they are
trivial, both reviewability and bisectability will improve from the
process.
You are doing a nice job improving the x86/asm/entry code, but if you
cannot create suitably conservative, maximally reviewable and
maximally bisectable patches to x86/asm then I won't be able to apply
assembly patches from you!
</rant>
Thanks,
Ingo
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