Re: [PATCH] RISC-V: Fix incorrect code of touching inaccessible memory address

[Kito Cheng <kito.cheng@sifive.com>]

I am a little hesitant about that, since I feel the vl and normal op
should be put in separately, otherwise the means of m_op_num is kind
of unclear, we have comments there but I think it's not ideal since it
is really context sensitive and hard to determine.

And I suspect gcc_assert (ops[m_op_num]); is not too useful since it
might just be out of range access if we forgot to pass the vl
operands.

I am thinking we might need to introduce something like llvm::ArrayRef
to have a better sanity check, e.g. check the length of ops.
One possible solution is just using std::vector can achieve the same
purpose too, but come with more cost.


On Wed, May 24, 2023 at 9:57 AM <juzhe.zhong@rivai.ai> wrote:
>
> From: Juzhe-Zhong <juzhe.zhong@rivai.ai>
>
> For VLMAX situation, rtx len = ops[m_op_num] is incorrect since
> the last element the ops array should be ops[m_op_num - 1];
>
> I notice this issue when I am debugging code.
> This is a code bug even though the following codes will hide this issue.
> We still should need this minor fix.
>
> Built && Regression PASSed.
>
> Ok for trunk?
>
> gcc/ChangeLog:
>
>         * config/riscv/riscv-v.cc: Fix bug of touching inaccessible memory.
>
> ---
>  gcc/config/riscv/riscv-v.cc | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/config/riscv/riscv-v.cc b/gcc/config/riscv/riscv-v.cc
> index fa61a850a22..a0992773644 100644
> --- a/gcc/config/riscv/riscv-v.cc
> +++ b/gcc/config/riscv/riscv-v.cc
> @@ -169,7 +169,11 @@ public:
>
>      if (m_needs_avl_p)
>        {
> -       rtx len = ops[m_op_num];
> +       /* The variable "m_op_num" means the real operation operands except VL
> +          operand. For VLMAX patterns (no VL operand), the last operand is
> +          ops[m_op_num -1]. Wheras for non-VLMAX patterns, the last operand is
> +          VL operand which is ops[m_op_num].  */
> +       rtx len = NULL_RTX;
>         if (m_vlmax_p)
>           {
>             if (const_vlmax_p (m_dest_mode))
> @@ -185,6 +189,20 @@ public:
>                 len = gen_reg_rtx (Pmode);
>                 emit_vlmax_vsetvl (m_dest_mode, len);
>               }
> +           else
> +             {
> +               /* According to LRA mov pattern in vector.md. The VL operand is
> +                  always the last operand.  */
> +               gcc_assert (ops[m_op_num]);
> +               len = ops[m_op_num];
> +             }
> +         }
> +       else
> +         {
> +           /* For non-VLMAX patterns. The VL operand is always the last
> +            * operand.  */
> +           gcc_assert (ops[m_op_num]);
> +           len = ops[m_op_num];
>           }
>         add_input_operand (len, Pmode);
>        }
> --
> 2.36.3
>