dotnet/runtime

Could emit branchless form of i <= 0b00111 && j <= 0b00111 for unsigned integers

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#92,692 opened on 2023/09/27

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説明

Similar to #61940, equivalent to (i | j) <= 0b0011, the constant value can be 2^n-1, also the condition can be <.

For example:

bool Test0(ulong x, ulong y) => x <= UInt32.MaxValue && y <= UInt32.MaxValue;

bool Test1(ulong x, ulong y) => (x | y) <= UInt32.MaxValue;

The JIT could produce the same output for the above, but currently not, see https://godbolt.org/z/G9Taxqcox

C:Test(ulong,ulong):ubyte:this (FullOpts):
       mov      eax, 0xD1FFAB1E
       cmp      rsi, rax
       ja       SHORT G_M42689_IG05
       mov      eax, 0xD1FFAB1E
       cmp      rdx, rax
       setbe    al
       movzx    rax, al
       ret      
G_M42689_IG05:
       xor      eax, eax
       ret      

C:Test1(ulong,ulong):ubyte:this (FullOpts):
       or       rdx, rsi
       mov      eax, 0xD1FFAB1E
       cmp      rdx, rax
       setbe    al
       movzx    rax, al
       ret      

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