* improve RiscV assembler optimizer

compiler/riscv/aoptcpurv.pas

@@ -332,7 +332,11 @@ implementation
          (taicpu(p).oper[2]^.typ=top_const) and
          (taicpu(p).oper[2]^.val=0) and
          GetNextInstructionUsingReg(p, hp1, taicpu(p).oper[0]^.reg) and
-         MatchInstruction(hp1, [A_SUB,A_ADD,A_SLL,A_SLT,A_AND,A_OR{$ifdef riscv64}{$endif}]) and
+         MatchInstruction(hp1, [A_SUB,A_ADD,A_SLL,A_SRL,A_SLT,A_AND,A_OR,
+           A_ADDI,A_ANDI,A_ORI,A_SRAI,A_SRLI,A_SLLI,A_XORI
+           {$ifdef riscv64},A_ADDIW,A_SLLIW,A_SRLIW,A_SRAIW,
+           A_ADDW,A_SLLW,A_SRLW,A_SUBW,A_SRAW{$endif}]
+           ) and
          (taicpu(hp1).ops=3) and
          (MatchOperand(taicpu(p).oper[0]^,taicpu(hp1).oper[2]^) or MatchOperand(taicpu(p).oper[0]^,taicpu(hp1).oper[1]^)) and
          (not RegModifiedBetween(taicpu(p).oper[1]^.reg, p,hp1)) and
@@ -622,6 +626,13 @@ implementation
                       RemoveInstr(p);
                       result:=true;
                     end
+                  else if (taicpu(p).oper[2]^.val=0) then
+                    begin
+                      { this enables further optimizations }
+                      DebugMsg('Peephole S*LI x,y,0 to addi performed', p);
+                      taicpu(p).opcode:=A_ADDI;
+                      result:=true;
+                    end
                   else
                     result:=OptPass1OP(p);
                 end;