[Bug c++/114747] New: [RISC-V RVV] Wrong SEW set for mixed-size intrinsics

[Bug c++/114747] New: [RISC-V RVV] Wrong SEW set for mixed-size intrinsics

[wojciech_mula at poczta dot onet.pl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114747

            Bug ID: 114747
           Summary: [RISC-V RVV] Wrong SEW set for mixed-size intrinsics
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wojciech_mula at poczta dot onet.pl
  Target Milestone: ---

This is a distilled procedure from simdutf project:

---
#include <cstdint>
#include <cstdlib>
#include <riscv_vector.h>

size_t convert_latin1_to_utf16le(const char *src, size_t len, char16_t *dst) {
  char16_t *beg = dst;
  for (size_t vl; len > 0; len -= vl, src += vl, dst += vl) {
    vl = __riscv_vsetvl_e8m4(len);
    vuint8m4_t v = __riscv_vle8_v_u8m4((uint8_t*)src, vl);
    __riscv_vse16_v_u16m8((uint16_t*)dst, __riscv_vzext_vf2_u16m8(v, vl), vl);
  }
  return dst - beg;
}
---

When compiled with gcc 13.2.0 with flags "-march=rv64gcv -O2" it sets a wrong
SEW:

---
convert_latin1_to_utf16le(char const*, unsigned long, char16_t*):
        beq     a1,zero,.L4
        mv      a4,a2
.L3:
        vsetvli a5,a1,e8,m4,ta,ma  # set SEW=8
        vle8.v  v8,0(a0)
        slli    a3,a5,1
        vzext.vf2       v24,v8     # illegal instruction, as SEW/2 < 8
        sub     a1,a1,a5
        vse16.v v24,0(a4)
        add     a0,a0,a5
        add     a4,a4,a3
        bne     a1,zero,.L3
        sub     a0,a4,a2
        srai    a0,a0,1
        ret
.L4:
        li      a0,0
        ret
---

The trunk available on godbold.org (riscv64-unknown-linux-gnu-g++ 14.0.1
20240415) emits vsetvli with e16 argument, which seems to be fine.

[Bug target/114747] [13 only] [RISC-V RVV] Wrong SEW set for mixed-size intrinsics

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114747

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.3

[Bug target/114747] [13 only] [RISC-V RVV] Wrong SEW set for mixed-size intrinsics

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114747

--- Comment #1 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Kito Cheng <kito@gcc.gnu.org>:

https://gcc.gnu.org/g:c4c0b0be87b4e08dab0e5e62c6f38a610a7423e7

commit r13-8701-gc4c0b0be87b4e08dab0e5e62c6f38a610a7423e7
Author: Kito Cheng <kito.cheng@sifive.com>
Date:   Mon May 6 23:45:22 2024 +0800

    RISC-V: Fix vsetvli local eliminate [PR114747]

    vsetvli local eliminate is only consider the current demand instead of
    full demand, and it will use that incomplete info to remove vsetvli.

    Give following example from PR114747:

    vsetvli a5,a1,e8,m4,ta,mu       # 57, ratio=2, sew=8, lmul=4
    vsetvli zero,a5,e16,m8,ta,ma    # 58, ratio=2, sew=16, lmul=8
    vle8.v  v8,0(a0)        # 13, demand ratio=2
    vzext.vf2       v24,v8  # 14, demand sew=16 and lmul=8

    Insn #58 will removed because #57 has satisfied demand of #13, but it's
    not consider #14.

    It should doing more demand analyze, but this bug only present in GCC 13
    branch, and we should not change too much on this release branch, so the
best
    way is make the check more conservative - remove only if the target
    vsetvl_discard_result having same SEW and LMUL as the source vsetvli.

    gcc/ChangeLog:

            PR target/114747
            * config/riscv/riscv-vsetvl.cc (local_eliminate_vsetvl_insn):
            Check target vsetvl_discard_result and source vsetvli has same
            SEW and LMUL.

    gcc/testsuite/ChangeLog:

            * gcc.target/riscv/rvv/vsetvl/pr114747.c: New.

[Bug target/114747] [13 only] [RISC-V RVV] Wrong SEW set for mixed-size intrinsics

[kito at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114747

Kito Cheng <kito at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Kito Cheng <kito at gcc dot gnu.org> ---
Fixed on gcc 13 branch, and GCC 13.3 will have the fix :)