Wrong (none) bypass usage by pv.cplxconj

Created by: Silabs-ArjanB

The pv.cplxconj instruction does not correctly use the register file bypasses. In the following example the pv.cplxconj.b should get its x12 operand from the preceding lui instruction. However, the register file bypass is not triggered and the wrong ALU operand is used for the pv.cplxconj.b instruction.

            Time          Cycles PC       Instr    Mnemonic
 86ns               4 00000180 00000013 nop                                 
 96ns               5 00000182 00000013 nop                                 
106ns               6 00000184 fffe3637 lui              x12, 0xfffe3000     x12=fffe3000
116ns               7 00000186 5cc19657 pv.cplxconj.b    x12, x3, x12        x12=00000000  x3:00000000 x12:00000000
126ns               8 0000018a 00000013 nop                                 
136ns               9 0000018c 00000013 nop                                 
146ns              10 0000018e 00000013 nop                                 

Wanted behavior is achieved for the following code (where I just inserted some nops so that the RTL would not have to rely on the register file bypass):

.section .text.start .global _start .type _start, @function

_start:

.word 0x00010001 lui x12,0xfffe3 nop nop nop .word 0x5cc19657 nop nop nop

Erroneous behavior is achieved for the following code:

.section .text.start .global _start .type _start, @function

_start:

.word 0x00010001 lui x12,0xfffe3 .word 0x5cc19657 nop nop nop

I believe (but didn't check) that the issue is caused by the following RTL in the 'decoder':

      6'b01011_1: begin // pv.cplxconj.h
        alu_operator_o       = ALU_ABS;
        is_clpx_o            = 1'b1;
        scalar_replication_o = 1'b0;
        **regb_used_o          = 1'b0;**
      end

My guess (without understanding what this instruction is supposed to do) is that regb_used_o needs to be 1.

Also note the related ticket https://github.com/openhwgroup/core-v-docs/issues/95 . The RTL code only mentions pv.cplxconj.h, whereas I think the above RTL handles both .h and .b. The documentation only mentions pv.cplxconj and does not mention the existence of pv.cplxconj.b, pv.cplxconj.h.