[Bug target/109279] RISC-V: complex constants synthesized should be improved

[vineet.gupta at linux dot dev via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109279

--- Comment #13 from Vineet Gupta <vineet.gupta at linux dot dev> ---
Ok it seems I missed _some_ improvement with prev change, although not ideal
still.

With 2e886eef7f2b

        li      a0,0x0101_0000
        addi    a0,a0,0x0101
        slli    a0,a0,16
        addi    a0,a0,0x0101
        slli    a0,a0,16
        addi    a0,a0,0x0101
        ret

Allow can_create_pseudo() in splitter

        li      a0,0x0101_0000
        addi    a5,a5,0x0101
        mv      a0,a5
        slli    a5,a5,32
        add     a0,a5,a0
        ret