Created
November 6, 2021 06:10
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Array Bounds Checks betwen .NET 5 and .NET 6. https://twitter.com/badamczewski01/status/1456711012099428359
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| // before .NET 5: Array Bound Check emitted. (BAD) | |
| // after .NET 6: Array Bound Check removed. (GOOD) | |
| void A(int[] a) | |
| { | |
| if (a.Length > 3) | |
| { | |
| a[0] = 1; | |
| a[1] = 2; | |
| a[2] = 3; | |
| } | |
| } |
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| L0000 sub rsp, 0x28 | |
| L0004 mov eax, [rcx+8] | |
| L0007 cmp eax, 3 | |
| L000a jle short L0030 | |
| L000c cmp eax, 0 | |
| L000f jbe short L0035 | |
| L0011 mov dword ptr [rcx+0x10], 1 | |
| L0018 cmp eax, 1 | |
| L001b jbe short L0035 | |
| L001d mov dword ptr [rcx+0x14], 2 | |
| L0024 cmp eax, 2 | |
| L0027 jbe short L0035 | |
| L0029 mov dword ptr [rcx+0x18], 3 | |
| L0030 add rsp, 0x28 | |
| L0034 ret | |
| L0035 call 0x00007ffa1f1eaac0 | |
| L003a int3 |
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| L0000 mov eax, [rcx+8] | |
| L0003 cmp eax, 3 | |
| L0006 jle short L001d | |
| L0008 mov dword ptr [rcx+0x10], 1 | |
| L000f mov dword ptr [rcx+0x14], 2 | |
| L0016 mov dword ptr [rcx+0x18], 3 | |
| L001d ret |
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| // before .NET 5: Array Bound Check emitted. (BAD) | |
| // after .NET 6: Array Bound Check removed. (GOOD) | |
| void A(int[] a) | |
| { | |
| if (a.Length < 3) // if > 3. Array Bounds check are emitted. | |
| return; | |
| a[0] = 1; | |
| a[1] = 2; | |
| a[2] = 3; | |
| } |
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| L0000 sub rsp, 0x28 | |
| L0004 mov eax, [rcx+8] | |
| L0007 cmp eax, 3 | |
| L000a jge short L0011 | |
| L000c add rsp, 0x28 | |
| L0010 ret | |
| L0011 cmp eax, 0 | |
| L0014 jbe short L003a | |
| L0016 mov dword ptr [rcx+0x10], 1 | |
| L001d cmp eax, 1 | |
| L0020 jbe short L003a | |
| L0022 mov dword ptr [rcx+0x14], 2 | |
| L0029 cmp eax, 2 | |
| L002c jbe short L003a | |
| L002e mov dword ptr [rcx+0x18], 3 | |
| L0035 add rsp, 0x28 | |
| L0039 ret | |
| L003a call 0x00007ffa1f1eaac0 | |
| L003f int3 |
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| L0000 mov eax, [rcx+8] | |
| L0003 cmp eax, 3 | |
| L0006 jge short L0009 | |
| L0008 ret | |
| L0009 mov dword ptr [rcx+0x10], 1 | |
| L0010 mov dword ptr [rcx+0x14], 2 | |
| L0017 mov dword ptr [rcx+0x18], 3 | |
| L001e ret |
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