Re: [PATCH] tcg/optimize: Fix folding of vector bitsel

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 19/9/25 14:49, WANG Rui wrote:
> It looks like a typo.

Likely from the TCG_TARGET_HAS_andc_vec case.

> When the false value (C) is the constant -1, the
> correct fold should be: R = B | ~A
> 
> Reproducer (LoongArch64 assembly):
> 
>       .text
>       .globl  _start
>   _start:
>       vldi    $vr1, 3073
>       vldi    $vr2, 1023
>       vbitsel.v       $vr0, $vr2, $vr1, $vr2
>       vpickve2gr.d    $a1, $vr0, 1
>       xori    $a0, $a1, 1
>       li.w    $a7, 93
>       syscall 0
> 
> Fixes: e58b977238e3 ("tcg/optimize: Optimize bitsel_vec")
> Link: https://github.com/llvm/llvm-project/issues/159610
> Signed-off-by: WANG Rui <wangrui@loongson.cn>
> ---
>   tcg/optimize.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tcg/optimize.c b/tcg/optimize.c
> index 3638ab9fea..f69702b26e 100644
> --- a/tcg/optimize.c
> +++ b/tcg/optimize.c
> @@ -1568,9 +1568,10 @@ static bool fold_bitsel_vec(OptContext *ctx, TCGOp *op)
>               return fold_and(ctx, op);
>           }
>           if (fv == -1 && TCG_TARGET_HAS_orc_vec) {
> +            TCGArg ta = op->args[2];
>               op->opc = INDEX_op_orc_vec;
>               op->args[2] = op->args[1];
> -            op->args[1] = op->args[3];
> +            op->args[1] = ta;
>               return fold_orc(ctx, op);
>           }
>       }
Looks correct, but I don't understand the swap. Can't we justkeep the 
same argument order for an ORC opcode? I'd have done:

-- >8 --
@@ -1569,8 +1569,6 @@ static bool fold_bitsel_vec(OptContext *ctx, TCGOp 
*op)
          }
          if (fv == -1 && TCG_TARGET_HAS_orc_vec) {
              op->opc = INDEX_op_orc_vec;
-            op->args[2] = op->args[1];
-            op->args[1] = op->args[3];
              return fold_orc(ctx, op);
          }
      }
---