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Remove redundant checks in advance if possible #412

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@Akeit0 Akeit0 commented Aug 3, 2025 •
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Redundant checks were not removed by the JIT because bufferLength was in the field and also because of the possibility of overflow.

I pasted JIT asm for reference.
It is recommended to separate the window to see main and pr at the same time.

Envitonment

.net9.0
Windows11
13th Gen Intel(R) Core(TM) i7-13700F   2.10 GHz
main 
; Assembly listing for method MemoryPack.MemoryPackWriter`1[System.__Canon]:WriteNullObjectHeader():this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 0 single block inlinees; 2 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rbx
       sub      rsp, 32
       mov      rbx, rcx

G_M000_IG02:                ;; offset=0x0008
       cmp      dword ptr [rbx+0x18], 0
       jg       SHORT G_M000_IG04

G_M000_IG03:                ;; offset=0x000E
       mov      rcx, rbx
       mov      r8d, 1
       call     [MemoryPack.MemoryPackWriter`1[System.__Canon]:RequestNewBuffer(int):this]

G_M000_IG04:                ;; offset=0x001D
       mov      rax, bword ptr [rbx+0x10]
       mov      byte  ptr [rax], 255
       mov      eax, dword ptr [rbx+0x18]
       dec      eax
       js       SHORT G_M000_IG06
       mov      dword ptr [rbx+0x18], eax
       inc      bword ptr [rbx+0x10]
       inc      dword ptr [rbx+0x1C]
       inc      dword ptr [rbx+0x24]

G_M000_IG05:                ;; offset=0x0038
       add      rsp, 32
       pop      rbx
       ret

G_M000_IG06:                ;; offset=0x003E
       call     [MemoryPack.MemoryPackSerializationException:ThrowInvalidAdvance()]
       int3

; Total bytes of code 69

; Assembly listing for method MemoryPack.MemoryPackWriter`1[System.__Canon]:WriteUnmanaged[int](byref):this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 0 single block inlinees; 2 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rsi
       push     rbx
       sub      rsp, 40
       mov      qword ptr [rsp+0x20], rdx
       mov      rbx, rcx
       mov      rsi, r8

G_M000_IG02:                ;; offset=0x0011
       mov      rcx, qword ptr [rdx+0x18]
       mov      rcx, qword ptr [rcx+0x10]
       test     rcx, rcx
       je       SHORT G_M000_IG07

G_M000_IG03:                ;; offset=0x001E
       mov      rdx, rcx

G_M000_IG04:                ;; offset=0x0021
       cmp      dword ptr [rbx+0x18], 4
       jge      SHORT G_M000_IG06

G_M000_IG05:                ;; offset=0x0027
       mov      rcx, rbx
       mov      r8d, 4
       call     [MemoryPack.MemoryPackWriter`1[System.__Canon]:RequestNewBuffer(int):this]

G_M000_IG06:                ;; offset=0x0036
       mov      rax, bword ptr [rbx+0x10]
       mov      ecx, dword ptr [rsi]
       mov      dword ptr [rax], ecx
       mov      eax, dword ptr [rbx+0x18]
       add      eax, -4
       jns      SHORT G_M000_IG08
       jmp      SHORT G_M000_IG10

G_M000_IG07:                ;; offset=0x0048
       mov      rcx, rdx
       mov      rdx, 0x7FF8A68682F8
       call     CORINFO_HELP_RUNTIMEHANDLE_METHOD
       mov      rdx, rax
       jmp      SHORT G_M000_IG04

G_M000_IG08:                ;; offset=0x005F
       mov      dword ptr [rbx+0x18], eax
       add      bword ptr [rbx+0x10], 4
       add      dword ptr [rbx+0x1C], 4
       add      dword ptr [rbx+0x20], 4

G_M000_IG09:                ;; offset=0x006F
       add      rsp, 40
       pop      rbx
       pop      rsi
       ret

G_M000_IG10:                ;; offset=0x0076
       call     [MemoryPack.MemoryPackSerializationException:ThrowInvalidAdvance()]
       int3

; Total bytes of code 125

; Assembly listing for method MemoryPack.MemoryPackReader:TryReadObjectHeader(byref):ubyte:this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 0 single block inlinees; 2 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rdi
       push     rsi
       push     rbx
       sub      rsp, 32
       mov      rbx, rcx
       mov      rsi, rdx

G_M000_IG02:                ;; offset=0x000D
       cmp      dword ptr [rbx+0x20], 0
       jg       SHORT G_M000_IG04

G_M000_IG03:                ;; offset=0x0013
       mov      rcx, rbx
       mov      edx, 1
       call     [MemoryPack.MemoryPackReader:GetNextSpan(int):byref:this]
       jmp      SHORT G_M000_IG05

G_M000_IG04:                ;; offset=0x0023
       mov      rax, bword ptr [rbx+0x18]

G_M000_IG05:                ;; offset=0x0027
       movzx    rcx, byte  ptr [rax]
       mov      byte  ptr [rsi], cl
       mov      edi, dword ptr [rbx+0x20]
       dec      edi
       jns      SHORT G_M000_IG07

G_M000_IG06:                ;; offset=0x0033
       mov      rcx, rbx
       mov      edx, 1
       call     [MemoryPack.MemoryPackReader:TryAdvanceSequence(int):ubyte:this]
       test     eax, eax
       jne      SHORT G_M000_IG08

G_M000_IG07:                ;; offset=0x0045
       mov      dword ptr [rbx+0x20], edi
       inc      bword ptr [rbx+0x18]
       inc      dword ptr [rbx+0x24]
       inc      dword ptr [rbx+0x28]

G_M000_IG08:                ;; offset=0x0052
       cmp      byte  ptr [rsi], 255
       setne    al
       movzx    rax, al

G_M000_IG09:                ;; offset=0x005B
       add      rsp, 32
       pop      rbx
       pop      rsi
       pop      rdi
       ret

; Total bytes of code 99

; Assembly listing for method MemoryPack.MemoryPackReader:ReadUnmanaged[int]():int:this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 0 single block inlinees; 2 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rdi
       push     rsi
       push     rbx
       sub      rsp, 32
       mov      rbx, rcx

G_M000_IG02:                ;; offset=0x000A
       cmp      dword ptr [rbx+0x20], 4
       jge      SHORT G_M000_IG04

G_M000_IG03:                ;; offset=0x0010
       mov      rcx, rbx
       mov      edx, 4
       call     [MemoryPack.MemoryPackReader:GetNextSpan(int):byref:this]
       jmp      SHORT G_M000_IG05

G_M000_IG04:                ;; offset=0x0020
       mov      rax, bword ptr [rbx+0x18]

G_M000_IG05:                ;; offset=0x0024
       mov      esi, dword ptr [rax]
       mov      edi, dword ptr [rbx+0x20]
       add      edi, -4
       jns      SHORT G_M000_IG07

G_M000_IG06:                ;; offset=0x002E
       mov      rcx, rbx
       mov      edx, 4
       call     [MemoryPack.MemoryPackReader:TryAdvanceSequence(int):ubyte:this]
       test     eax, eax
       jne      SHORT G_M000_IG08

G_M000_IG07:                ;; offset=0x0040
       mov      dword ptr [rbx+0x20], edi
       add      bword ptr [rbx+0x18], 4
       add      dword ptr [rbx+0x24], 4
       add      dword ptr [rbx+0x28], 4

G_M000_IG08:                ;; offset=0x0050
       mov      eax, esi

G_M000_IG09:                ;; offset=0x0052
       add      rsp, 32
       pop      rbx
       pop      rsi
       pop      rdi
       ret

; Total bytes of code 90

; Assembly listing for method MemoryPack.MemoryPackReader:ReadUnmanaged[int](byref):this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 0 single block inlinees; 2 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rsi
       push     rbx
       sub      rsp, 40
       mov      rbx, rcx
       mov      rsi, rdx

G_M000_IG02:                ;; offset=0x000C
       cmp      dword ptr [rbx+0x20], 4
       jge      SHORT G_M000_IG04

G_M000_IG03:                ;; offset=0x0012
       mov      rcx, rbx
       mov      edx, 4
       call     [MemoryPack.MemoryPackReader:GetNextSpan(int):byref:this]
       jmp      SHORT G_M000_IG05

G_M000_IG04:                ;; offset=0x0022
       mov      rax, bword ptr [rbx+0x18]

G_M000_IG05:                ;; offset=0x0026
       mov      ecx, dword ptr [rax]
       mov      dword ptr [rsi], ecx
       mov      esi, dword ptr [rbx+0x20]
       add      esi, -4
       jns      SHORT G_M000_IG07

G_M000_IG06:                ;; offset=0x0032
       mov      rcx, rbx
       mov      edx, 4
       call     [MemoryPack.MemoryPackReader:TryAdvanceSequence(int):ubyte:this]
       test     eax, eax
       jne      SHORT G_M000_IG08

G_M000_IG07:                ;; offset=0x0044
       mov      dword ptr [rbx+0x20], esi
       add      bword ptr [rbx+0x18], 4
       add      dword ptr [rbx+0x24], 4
       add      dword ptr [rbx+0x28], 4

G_M000_IG08:                ;; offset=0x0054
       add      rsp, 40
       pop      rbx
       pop      rsi
       ret

; Total bytes of code 91
pr 
; Assembly listing for method MemoryPack.MemoryPackWriter`1[System.__Canon]:WriteNullObjectHeader():this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 1 single block inlinees; 1 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rbx
       sub      rsp, 32
       mov      rbx, rcx

G_M000_IG02:                ;; offset=0x0008
       cmp      dword ptr [rbx+0x18], 0
       jg       SHORT G_M000_IG04

G_M000_IG03:                ;; offset=0x000E
       mov      rcx, rbx
       mov      r8d, 1
       call     [MemoryPack.MemoryPackWriter`1[System.__Canon]:RequestNewBuffer(int):this]

G_M000_IG04:                ;; offset=0x001D
       mov      rax, bword ptr [rbx+0x10]
       mov      byte  ptr [rax], 255
       dec      dword ptr [rbx+0x18]
       inc      bword ptr [rbx+0x10]
       inc      dword ptr [rbx+0x1C]
       inc      dword ptr [rbx+0x24]

G_M000_IG05:                ;; offset=0x0031
       add      rsp, 32
       pop      rbx
       ret

; Total bytes of code 55

; Assembly listing for method MemoryPack.MemoryPackWriter`1[System.__Canon]:WriteUnmanaged[int](byref):this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 1 single block inlinees; 1 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rsi
       push     rbx
       sub      rsp, 40
       mov      qword ptr [rsp+0x20], rdx
       mov      rbx, rcx
       mov      rsi, r8

G_M000_IG02:                ;; offset=0x0011
       mov      rcx, qword ptr [rdx+0x18]
       mov      rcx, qword ptr [rcx+0x10]
       test     rcx, rcx
       je       SHORT G_M000_IG08

G_M000_IG03:                ;; offset=0x001E
       mov      rdx, rcx

G_M000_IG04:                ;; offset=0x0021
       cmp      dword ptr [rbx+0x18], 4
       jge      SHORT G_M000_IG06

G_M000_IG05:                ;; offset=0x0027
       mov      rcx, rbx
       mov      r8d, 4
       call     [MemoryPack.MemoryPackWriter`1[System.__Canon]:RequestNewBuffer(int):this]

G_M000_IG06:                ;; offset=0x0036
       mov      rax, bword ptr [rbx+0x10]
       mov      ecx, dword ptr [rsi]
       mov      dword ptr [rax], ecx
       add      bword ptr [rbx+0x10], 4
       add      dword ptr [rbx+0x18], -4
       add      dword ptr [rbx+0x1C], 4
       add      dword ptr [rbx+0x20], 4

G_M000_IG07:                ;; offset=0x004F
       add      rsp, 40
       pop      rbx
       pop      rsi
       ret

G_M000_IG08:                ;; offset=0x0056
       mov      rcx, rdx
       mov      rdx, 0x7FF8A68684A8
       call     CORINFO_HELP_RUNTIMEHANDLE_METHOD
       mov      rdx, rax
       jmp      SHORT G_M000_IG04

; Total bytes of code 109

; Assembly listing for method MemoryPack.MemoryPackReader:TryReadObjectHeader(byref):ubyte:this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 1 single block inlinees; 1 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rsi
       push     rbx
       sub      rsp, 40
       mov      rbx, rcx
       mov      rsi, rdx

G_M000_IG02:                ;; offset=0x000C
       cmp      dword ptr [rbx+0x20], 0
       jg       SHORT G_M000_IG04

G_M000_IG03:                ;; offset=0x0012
       mov      rcx, rbx
       mov      edx, 1
       call     [MemoryPack.MemoryPackReader:GetNextSpan(int):byref:this]
       jmp      SHORT G_M000_IG05

G_M000_IG04:                ;; offset=0x0022
       mov      rax, bword ptr [rbx+0x18]

G_M000_IG05:                ;; offset=0x0026
       movzx    rax, byte  ptr [rax]
       mov      byte  ptr [rsi], al
       dec      dword ptr [rbx+0x20]
       inc      bword ptr [rbx+0x18]
       inc      dword ptr [rbx+0x24]
       inc      dword ptr [rbx+0x28]
       cmp      byte  ptr [rsi], 255
       setne    al
       movzx    rax, al

G_M000_IG06:                ;; offset=0x0041
       add      rsp, 40
       pop      rbx
       pop      rsi
       ret

; Total bytes of code 72

; Assembly listing for method MemoryPack.MemoryPackReader:ReadUnmanaged[int]():int:this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 1 single block inlinees; 1 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rbx
       sub      rsp, 32
       mov      rbx, rcx

G_M000_IG02:                ;; offset=0x0008
       cmp      dword ptr [rbx+0x20], 4
       jge      SHORT G_M000_IG04

G_M000_IG03:                ;; offset=0x000E
       mov      rcx, rbx
       mov      edx, 4
       call     [MemoryPack.MemoryPackReader:GetNextSpan(int):byref:this]
       jmp      SHORT G_M000_IG05

G_M000_IG04:                ;; offset=0x001E
       mov      rax, bword ptr [rbx+0x18]

G_M000_IG05:                ;; offset=0x0022
       mov      eax, dword ptr [rax]
       add      dword ptr [rbx+0x20], -4
       add      bword ptr [rbx+0x18], 4
       add      dword ptr [rbx+0x24], 4
       add      dword ptr [rbx+0x28], 4

G_M000_IG06:                ;; offset=0x0035
       add      rsp, 32
       pop      rbx
       ret

; Total bytes of code 59

; Assembly listing for method MemoryPack.MemoryPackReader:ReadUnmanaged[int](byref):this (FullOpts)
; Emitting BLENDED_CODE for X64 with AVX - Windows
; FullOpts code
; optimized code
; rsp based frame
; partially interruptible
; No PGO data
; 0 inlinees with PGO data; 1 single block inlinees; 1 inlinees without PGO data

G_M000_IG01:                ;; offset=0x0000
       push     rsi
       push     rbx
       sub      rsp, 40
       mov      rbx, rcx
       mov      rsi, rdx

G_M000_IG02:                ;; offset=0x000C
       cmp      dword ptr [rbx+0x20], 4
       jge      SHORT G_M000_IG04

G_M000_IG03:                ;; offset=0x0012
       mov      rcx, rbx
       mov      edx, 4
       call     [MemoryPack.MemoryPackReader:GetNextSpan(int):byref:this]
       jmp      SHORT G_M000_IG05

G_M000_IG04:                ;; offset=0x0022
       mov      rax, bword ptr [rbx+0x18]

G_M000_IG05:                ;; offset=0x0026
       mov      eax, dword ptr [rax]
       mov      dword ptr [rsi], eax
       add      dword ptr [rbx+0x20], -4
       add      bword ptr [rbx+0x18], 4
       add      dword ptr [rbx+0x24], 4
       add      dword ptr [rbx+0x28], 4

G_M000_IG06:                ;; offset=0x003B
       add      rsp, 40
       pop      rbx
       pop      rsi
       ret

; Total bytes of code 66

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@Akeit0