deps: bump windows-sys from 0.60.2 to 0.61.2 - #6
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The +0.47 Ir/op batch_lifo/batch_fifo gap — the one op we lose to mimalloc — is
now localized precisely, and it is NOT algorithmic. Per-function callgrind plus a
direct disassembly of both allocators' free:
- malloc is at PARITY (ra 15.99/op == mi 15.99/op). The whole gap is in free.
- free fast path, executed: ours 27 insns, mimalloc 24 (excl. its CET
endbr64). The +3, instruction for instruction:
* used-- decrement, +3: mimalloc emits "subw $1, [used]; je" — one
memory-destination RMW feeding the retire branch (2 insns). We emit
load / dec / store / test / branch (5). LLVM won't select "dec [mem]; jle"
because the decremented value must be in memory before the branch (the
retire tail re-reads used) AND drive the branch.
* thread compare, +1: mimalloc "cmp %rcx, %fs:0" (TLS self-pointer as a cmp
operand); we "mov %fs:0,%rcx" then cmp, because thread_id() is an
inline-asm "mov fs:0" that forces a register.
* idx * sizeof(Page), -1: we use one imul where mimalloc uses lea+shl — a
place we are already tighter.
Attempted the obvious fix — split the list-push from the used decrement and
inline the decrement next to the branch, the shape most likely to trigger
"dec [mem]". Result: BYTE-IDENTICAL asm, same mov/dec/mov/test/jle at the same
addresses. Reverted. C's "--page->used <= 0" gets "subw; je" from Clang; the
equivalent Rust does not, and neither fold is reachable without inline asm on the
hottest path in the allocator.
So the batch gap is a Rust-vs-C instruction-selection floor. Closing the last
~0.5% on one synthetic op would take inline asm in free — not worth it against a
path we win on every other op and match on real programs. This commit ships no
logic change: only a NOTE at the decrement so the dead end is not re-explored,
and the full trace in docs/opps.md #6. Verified byte-identical (free disasm
unchanged) and tests green.
Co-Authored-By: Claude Fable 5 (1M context) <noreply@anthropic.com>
Bumps [windows-sys](https://github.com/microsoft/windows-rs) from 0.60.2 to 0.61.2. - [Release notes](https://github.com/microsoft/windows-rs/releases) - [Commits](https://github.com/microsoft/windows-rs/commits) --- updated-dependencies: - dependency-name: windows-sys dependency-version: 0.61.2 dependency-type: direct:production update-type: version-update:semver-minor ... Signed-off-by: dependabot[bot] <support@github.com>
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Bumps windows-sys from 0.60.2 to 0.61.2.
Release notes
Sourced from windows-sys's releases.
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