Jim Lin d395043300 [RISCV] Select unsigned bitfield insert for XAndesPerf (#142737) ...

The XAndesPerf extension includes unsigned bitfield extraction
instruction `NDS.BFOZ`, which can extract the bits from 0 to Len -1,
place them starting at bit Msb, and zero-fills the remaining bits.

This patch handles the cases where Msb < Lsb for `NDS.BFOZ`.

Instruction Sytax:

    nds.bfoz Rd, Rs1, Msb, Lsb

The operation is:

    if Msb < Lsb:
        Lenm1 = Lsb - Msb;
        Rd[Lsb:Msb] = Rs1[Lenm1:0];
        if (Lsb < (XLen -1)) Rd[XLen-1:Lsb+1]=0;
        Rd[Msb-1:0]=0;

When Len == 1, it is a special case where the Msb is set to 0 instead of
being equal to the Lsb.

2025-06-06 09:02:18 +08:00

156 KiB

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