[Bug target/116035] New: [14/15] RISC-V: -march=rv64g_xtheadmemidx_zba generates illegal lwu insn

[patrick at rivosinc dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116035

            Bug ID: 116035
           Summary: [14/15] RISC-V: -march=rv64g_xtheadmemidx_zba
                    generates illegal lwu insn
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick at rivosinc dot com
  Target Milestone: ---

Testcase:
void a(long);
unsigned b[11];
void c() {
  for (int d = 0; d < 11; ++d)
    a(b[d]);
}

Generated asm:
c:
        addi    sp,sp,-32
        sd      s0,16(sp)
        lui     s0,%hi(.LANCHOR0)
        addi    s0,s0,%lo(.LANCHOR0)
        sd      s1,8(sp)
        sd      ra,24(sp)
        addi    s1,s0,44
.L2:
        lwu     a0,(s0),4,0
        call    a
        bne     s0,s1,.L2
        ld      ra,24(sp)
        ld      s0,16(sp)
        ld      s1,8(sp)
        addi    sp,sp,32
        jr      ra
b:
        .zero   44

Command/backtrace:
> /scratch/tc-testing/tc-compiler-fuzz-trunk/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64g_xtheadmemidx_zba -mabi=lp64d -mabi=lp64d driver.c -c -O3
/scratch/tmp/ccJK0u5H.s: Assembler messages:
/scratch/tmp/ccJK0u5H.s:25: Error: illegal operands `lwu a0,(s0),4,0'

Godbolt: https://godbolt.org/z/874e85n9r

Without xtheadmemidx: https://godbolt.org/z/4Eo4Wf6h3

Found via fuzzer.

Very likely related to: pr116033