[Bug target/116131] New: [14/15 Regression] RISC-V: Unrecognizable insn with xtheadmemidx

[patrick at rivosinc dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116131

            Bug ID: 116131
           Summary: [14/15 Regression] RISC-V: Unrecognizable insn with
                    xtheadmemidx
           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:
volatile long long a;
int b;
int c[1];
void d() { c[a] = b; }

Command/backtrace:
> /scratch/tc-testing/tc-compiler-fuzz-trunk/build-gcv/bin/riscv64-unknown-linux-gnu-gcc -march=rv32ixtheadmemidx -mabi=ilp32 -O1 red.c -c -S -o /dev/null
red.c: In function 'd':
red.c:4:22: error: unrecognizable insn:
    4 | void d() { c[a] = b; }
      |                      ^
(insn 17 13 0 2 (set (mem:SI (plus:SI (reg/f:SI 141)
                (ashift:SI (subreg:SI (reg:DI 134 [ a.0_1 ]) 0)
                    (const_int 2 [0x2]))) [0  S4 A32])
        (reg:SI 143 [ b ])) "red.c":4:17 -1
     (nil))
during RTL pass: subreg3
red.c:4:22: internal compiler error: in extract_insn, at recog.cc:2848
0x2ddf545 internal_error(char const*, ...)
        ../../../gcc/gcc/diagnostic-global-context.cc:491
0xc4f10e fancy_abort(char const*, int, char const*)
        ../../../gcc/gcc/diagnostic.cc:1755
0xae2985 _fatal_insn(char const*, rtx_def const*, char const*, int, char
const*)
        ../../../gcc/gcc/rtl-error.cc:108
0xae29a7 _fatal_insn_not_found(rtx_def const*, char const*, int, char const*)
        ../../../gcc/gcc/rtl-error.cc:116
0xae125b extract_insn(rtx_insn*)
        ../../../gcc/gcc/recog.cc:2848
0x2800737 decompose_multiword_subregs
        ../../../gcc/gcc/lower-subreg.cc:1584
0x28016f1 execute
        ../../../gcc/gcc/lower-subreg.cc:1849
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.


Godbolt: https://godbolt.org/z/Gc1a5Mxfd

Found via fuzzer.