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Fix TrailingSliceLayout and remove Split::via_unaligned #3659

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Merged
joshlf merged 1 commit into from
Oct 5, 2026
Merged

Fix TrailingSliceLayout and remove Split::via_unaligned #3659

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7 changes: 7 additions & 0 deletions zerocopy/AGENTS.md
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Expand Up @@ -41,6 +41,13 @@ These instructions apply to work in the `zerocopy/` subtree.
In Markdown, indent wrapped bullet continuation lines by two spaces and put a
blank line after each section heading.

- **Derived traits in tests:** For traits whose documentation requires
derive-only implementation, test fixture types **MUST** use Zerocopy's
derives. Do not bypass a derive rejection with a manual implementation;
instead, test the lower-level internal primitive or extend the derive.
Generated derive-output snapshots and crate-owned built-in implementations
are exempt.

## Task-Specific Skills

Use the applicable skills in addition to these standing rules. Skills compose;
Expand Down
31 changes: 15 additions & 16 deletions zerocopy/benches/ref_from_bytes_dynamic_padding.x86-64
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@@ -1,22 +1,21 @@
bench_ref_from_bytes_dynamic_padding:
test dil, 3
jne .LBB5_3
movabs rax, 9223372036854775804
and rax, rsi
cmp rax, 9
jb .LBB5_3
add rax, -9
cmp rsi, 12
setae al
mov ecx, esi
or ecx, edi
test cl, 3
sete cl
and cl, al
cmp cl, 1
je .LBB5_2
xor edi, edi
mov rax, rdi
ret
.LBB5_2:
add rsi, -9
movabs rcx, -6148914691236517205
mov rax, rsi
mul rcx
shr rdx
lea rax, [rdx + 2*rdx]
or rax, 3
add rax, 9
cmp rsi, rax
je .LBB5_4
.LBB5_3:
xor edi, edi
mov rdx, rsi
.LBB5_4:
mov rax, rdi
ret
70 changes: 35 additions & 35 deletions zerocopy/benches/ref_from_bytes_dynamic_padding.x86-64.mca
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Original file line number Diff line number Diff line change
@@ -1,11 +1,11 @@
Iterations: 100
Instructions: 1900
Total Cycles: 645
Total Cycles: 641
Total uOps: 2000

Dispatch Width: 4
uOps Per Cycle: 3.10
IPC: 2.95
uOps Per Cycle: 3.12
IPC: 2.96
Block RThroughput: 5.0


Expand All @@ -18,23 +18,23 @@ Instruction Info:
[6]: HasSideEffects (U)

[1] [2] [3] [4] [5] [6] Instructions:
1 1 0.33 test dil, 3
1 1 1.00 jne .LBB5_3
1 1 0.33 movabs rax, 9223372036854775804
1 1 0.33 and rax, rsi
1 1 0.33 cmp rax, 9
1 1 1.00 jb .LBB5_3
1 1 0.33 add rax, -9
1 1 0.33 cmp rsi, 12
1 1 0.50 setae al
1 1 0.33 mov ecx, esi
1 1 0.33 or ecx, edi
1 1 0.33 test cl, 3
1 1 0.50 sete cl
1 1 0.33 and cl, al
1 1 0.33 cmp cl, 1
1 1 1.00 je .LBB5_2
1 0 0.25 xor edi, edi
1 1 0.33 mov rax, rdi
1 1 1.00 U ret
1 1 0.33 add rsi, -9
1 1 0.33 movabs rcx, -6148914691236517205
1 1 0.33 mov rax, rsi
2 4 1.00 mul rcx
1 1 0.50 shr rdx
1 1 0.50 lea rax, [rdx + 2*rdx]
1 1 0.33 or rax, 3
1 1 0.33 add rax, 9
1 1 0.33 cmp rsi, rax
1 1 1.00 je .LBB5_4
1 0 0.25 xor edi, edi
1 1 0.33 mov rdx, rsi
1 1 0.33 mov rax, rdi
1 1 1.00 U ret

Expand All @@ -52,26 +52,26 @@ Resources:

Resource pressure per iteration:
[0] [1] [2] [3] [4] [5] [6.0] [6.1]
- - 6.32 6.33 - 6.35 - -
- - 6.33 6.33 - 6.34 - -

Resource pressure by instruction:
[0] [1] [2] [3] [4] [5] [6.0] [6.1] Instructions:
- - 0.64 0.35 - 0.01 - - test dil, 3
- - - - - 1.00 - - jne .LBB5_3
- - 0.34 0.65 - 0.01 - - movabs rax, 9223372036854775804
- - 0.35 0.65 - - - - and rax, rsi
- - 0.33 0.34 - 0.33 - - cmp rax, 9
- - - - - 1.00 - - jb .LBB5_3
- - 0.35 - - 0.65 - - add rax, -9
- - 0.97 0.01 - 0.02 - - movabs rcx, -6148914691236517205
- - 1.00 1.00 - - - - mul rcx
- - 0.99 - - 0.01 - - shr rdx
- - 0.33 0.67 - - - - lea rax, [rdx + 2*rdx]
- - 0.34 0.66 - - - - or rax, 3
- - 0.33 0.66 - 0.01 - - add rax, 9
- - 0.01 0.99 - - - - cmp rsi, rax
- - - - - 1.00 - - je .LBB5_4
- - 0.99 - - 0.01 - - cmp rsi, 12
- - 1.00 - - - - - setae al
- - - 0.34 - 0.66 - - mov ecx, esi
- - - 0.99 - 0.01 - - or ecx, edi
- - - 1.00 - - - - test cl, 3
- - 0.67 - - 0.33 - - sete cl
- - - 1.00 - - - - and cl, al
- - - 1.00 - - - - cmp cl, 1
- - - - - 1.00 - - je .LBB5_2
- - - - - - - - xor edi, edi
- - 0.32 0.01 - 0.67 - - mov rdx, rsi
- - 0.02 0.34 - 0.64 - - mov rax, rdi
- - 0.66 - - 0.34 - - mov rax, rdi
- - - - - 1.00 - - ret
- - 0.35 0.01 - 0.64 - - add rsi, -9
- - 0.65 0.33 - 0.02 - - movabs rcx, -6148914691236517205
- - 0.01 0.33 - 0.66 - - mov rax, rsi
- - 1.00 1.00 - - - - mul rcx
- - 1.00 - - - - - shr rdx
- - - 0.33 - 0.67 - - mov rax, rdi
- - - - - 1.00 - - ret
21 changes: 6 additions & 15 deletions zerocopy/benches/ref_from_bytes_dynamic_size.x86-64
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Original file line number Diff line number Diff line change
@@ -1,20 +1,11 @@
bench_ref_from_bytes_dynamic_size:
mov rdx, rsi
cmp rsi, 4
setb al
or al, dil
test al, 1
je .LBB5_2
mov ecx, edx
or ecx, edi
xor eax, eax
ret
.LBB5_2:
lea rcx, [rdx - 4]
mov rsi, rcx
and rsi, -2
add rsi, 4
shr rcx
xor eax, eax
cmp rdx, rsi
cmove rdx, rcx
sub rdx, 4
cmovb rdi, rax
shr rdx
test cl, 1
cmove rax, rdi
ret
58 changes: 21 additions & 37 deletions zerocopy/benches/ref_from_bytes_dynamic_size.x86-64.mca
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Original file line number Diff line number Diff line change
@@ -1,12 +1,12 @@
Iterations: 100
Instructions: 1800
Total Cycles: 704
Total uOps: 2000
Instructions: 1000
Total Cycles: 373
Total uOps: 1200

Dispatch Width: 4
uOps Per Cycle: 2.84
IPC: 2.56
Block RThroughput: 5.0
uOps Per Cycle: 3.22
IPC: 2.68
Block RThroughput: 3.0


Instruction Info:
Expand All @@ -19,21 +19,13 @@ Instruction Info:

[1] [2] [3] [4] [5] [6] Instructions:
1 1 0.33 mov rdx, rsi
1 1 0.33 cmp rsi, 4
1 1 0.50 setb al
1 1 0.33 or al, dil
1 1 0.33 test al, 1
1 1 1.00 je .LBB5_2
1 1 0.33 mov ecx, edx
1 1 0.33 or ecx, edi
1 0 0.25 xor eax, eax
1 1 1.00 U ret
1 1 0.50 lea rcx, [rdx - 4]
1 1 0.33 mov rsi, rcx
1 1 0.33 and rsi, -2
1 1 0.33 add rsi, 4
1 1 0.50 shr rcx
1 0 0.25 xor eax, eax
1 1 0.33 cmp rdx, rsi
2 2 0.67 cmove rdx, rcx
1 1 0.33 sub rdx, 4
2 2 0.67 cmovb rdi, rax
1 1 0.50 shr rdx
1 1 0.33 test cl, 1
2 2 0.67 cmove rax, rdi
1 1 1.00 U ret

Expand All @@ -51,25 +43,17 @@ Resources:

Resource pressure per iteration:
[0] [1] [2] [3] [4] [5] [6.0] [6.1]
- - 5.97 5.98 - 6.05 - -
- - 3.66 3.67 - 3.67 - -

Resource pressure by instruction:
[0] [1] [2] [3] [4] [5] [6.0] [6.1] Instructions:
- - 0.97 0.01 - 0.02 - - mov rdx, rsi
- - 0.01 0.02 - 0.97 - - cmp rsi, 4
- - 0.03 - - 0.97 - - setb al
- - 0.01 0.02 - 0.97 - - or al, dil
- - - 0.98 - 0.02 - - test al, 1
- - - - - 1.00 - - je .LBB5_2
- - - - - - - - xor eax, eax
- - - - - 1.00 - - ret
- - 0.98 0.02 - - - - lea rcx, [rdx - 4]
- - 0.01 0.99 - - - - mov rsi, rcx
- - - 0.98 - 0.02 - - and rsi, -2
- - 0.98 0.01 - 0.01 - - add rsi, 4
- - 0.99 - - 0.01 - - shr rcx
- - 0.32 0.01 - 0.67 - - mov rdx, rsi
- - 0.33 0.35 - 0.32 - - mov ecx, edx
- - 0.01 0.34 - 0.65 - - or ecx, edi
- - - - - - - - xor eax, eax
- - 0.02 0.97 - 0.01 - - cmp rdx, rsi
- - 0.99 0.99 - 0.02 - - cmove rdx, rcx
- - 0.98 0.99 - 0.03 - - cmove rax, rdi
- - 0.67 0.33 - - - - sub rdx, 4
- - 0.99 0.98 - 0.03 - - cmovb rdi, rax
- - 0.03 - - 0.97 - - shr rdx
- - 0.32 0.67 - 0.01 - - test cl, 1
- - 0.99 0.99 - 0.02 - - cmove rax, rdi
- - - - - 1.00 - - ret
14 changes: 7 additions & 7 deletions zerocopy/benches/ref_from_prefix_dynamic_padding.x86-64
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Original file line number Diff line number Diff line change
@@ -1,19 +1,19 @@
bench_ref_from_prefix_dynamic_padding:
test dil, 3
sete al
cmp rsi, 12
setae cl
test al, cl
jne .LBB5_2
movabs rax, 9223372036854775804
and rsi, rax
cmp rsi, 8
ja .LBB5_3
.LBB5_2:
xor edx, edx
test dil, 3
sete dl
xor edi, edi
mov rax, rdi
ret
.LBB5_3:
add rsi, -9
.LBB5_2:
or rsi, 3
add rsi, -12
movabs rcx, -6148914691236517205
mov rax, rsi
mul rcx
Expand Down
48 changes: 25 additions & 23 deletions zerocopy/benches/ref_from_prefix_dynamic_padding.x86-64.mca
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Original file line number Diff line number Diff line change
@@ -1,12 +1,12 @@
Iterations: 100
Instructions: 1900
Total Cycles: 607
Total uOps: 2000
Instructions: 2000
Total Cycles: 640
Total uOps: 2100

Dispatch Width: 4
uOps Per Cycle: 3.29
uOps Per Cycle: 3.28
IPC: 3.13
Block RThroughput: 5.0
Block RThroughput: 5.3


Instruction Info:
Expand All @@ -19,18 +19,19 @@ Instruction Info:

[1] [2] [3] [4] [5] [6] Instructions:
1 1 0.33 test dil, 3
1 1 0.50 sete al
1 1 0.33 cmp rsi, 12
1 1 0.50 setae cl
1 1 0.33 test al, cl
1 1 1.00 jne .LBB5_2
1 1 0.33 movabs rax, 9223372036854775804
1 1 0.33 and rsi, rax
1 1 0.33 cmp rsi, 8
1 1 1.00 ja .LBB5_3
1 0 0.25 xor edx, edx
1 1 0.33 test dil, 3
1 1 0.50 sete dl
1 0 0.25 xor edi, edi
1 1 0.33 mov rax, rdi
1 1 1.00 U ret
1 1 0.33 add rsi, -9
1 1 0.33 or rsi, 3
1 1 0.33 add rsi, -12
1 1 0.33 movabs rcx, -6148914691236517205
1 1 0.33 mov rax, rsi
2 4 1.00 mul rcx
Expand All @@ -52,26 +53,27 @@ Resources:

Resource pressure per iteration:
[0] [1] [2] [3] [4] [5] [6.0] [6.1]
- - 6.00 5.99 - 6.01 - -
- - 6.33 6.33 - 6.34 - -

Resource pressure by instruction:
[0] [1] [2] [3] [4] [5] [6.0] [6.1] Instructions:
- - 0.01 0.98 - 0.01 - - test dil, 3
- - 0.65 0.34 - 0.01 - - test dil, 3
- - 0.99 - - 0.01 - - sete al
- - 0.01 0.33 - 0.66 - - cmp rsi, 12
- - 0.34 - - 0.66 - - setae cl
- - 1.00 - - - - - test al, cl
- - - - - 1.00 - - jne .LBB5_2
- - 0.98 0.01 - 0.01 - - movabs rax, 9223372036854775804
- - 0.01 0.99 - - - - and rsi, rax
- - 0.01 0.99 - - - - cmp rsi, 8
- - - - - 1.00 - - ja .LBB5_3
- - - - - - - - xor edx, edx
- - 0.99 0.01 - - - - test dil, 3
- - 0.99 - - 0.01 - - sete dl
- - - 0.99 - 0.01 - - test dil, 3
- - - - - 1.00 - - sete dl
- - - - - - - - xor edi, edi
- - - 0.01 - 0.99 - - mov rax, rdi
- - - 1.00 - - - - mov rax, rdi
- - - - - 1.00 - - ret
- - 0.01 0.99 - - - - add rsi, -9
- - - 1.00 - - - - movabs rcx, -6148914691236517205
- - 1.00 - - - - - mov rax, rsi
- - 0.01 0.99 - - - - or rsi, 3
- - 0.33 0.67 - - - - add rsi, -12
- - 0.66 0.34 - - - - movabs rcx, -6148914691236517205
- - 0.34 0.33 - 0.33 - - mov rax, rsi
- - 1.00 1.00 - - - - mul rcx
- - 1.00 - - - - - shr rdx
- - - 0.01 - 0.99 - - mov rax, rdi
- - - 0.34 - 0.66 - - mov rax, rdi
- - - - - 1.00 - - ret
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