[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.
llvm-project
d3950433 - [RISCV] Select unsigned bitfield insert for XAndesPerf (#142737)
