[X86] Missed Fold: `vgf2p8affineqb(x, m, imm8) ^ C` => `vgf2p8affineqb(x, m, imm8 ^ C)`

[WalterKruger]

The immediate in the vgf2p8affineqb instruction applies a XOR after the main affine transformation. This can be folded with standalone XORs by any splatted 8-bit constants.

affineNot_clang:
        gf2p8affineqb   xmm0, xmm1, 0
        pcmpeqd xmm1, xmm1
        pxor    xmm0, xmm1
        ret

affineNot_tgt:
        gf2p8affineqb   xmm0, xmm1, 255
        ret

https://godbolt.org/z/4qhG5fGq3

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Walter (WalterKruger)

Details

The immediate in the `vgf2p8affineqb` instruction applies a XOR after the main affine transformation. This can be folded with standalone XORs by any splatted 8-bit constants.

affineNot_clang:
        gf2p8affineqb   xmm0, xmm1, 0
        pcmpeqd xmm1, xmm1
        pxor    xmm0, xmm1
        ret

affineNot_tgt:
        gf2p8affineqb   xmm0, xmm1, 255
        ret

https://godbolt.org/z/4qhG5fGq3

[bala-bhargav]

@WalterKruger
i would like to work on this issue .