On Wed, 16 Aug 2023 at 15:58, Richard Henderson
<richard.hender...@linaro.org> wrote:
>
> Inserting a zero into a value, or inserting a value
> into zero at offset 0 my be implemented with AND.
>
> Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
> ---
> tcg/optimize.c | 35 +++++++++++++++++++++++++++++++++++
> 1 file changed, 35 insertions(+)
>
> diff --git a/tcg/optimize.c b/tcg/optimize.c
> index d2156367a3..956114b631 100644
> --- a/tcg/optimize.c
> +++ b/tcg/optimize.c
> @@ -1279,6 +1279,8 @@ static bool fold_ctpop(OptContext *ctx, TCGOp *op)
>
> static bool fold_deposit(OptContext *ctx, TCGOp *op)
> {
> + TCGOpcode and_opc;
> +
> if (arg_is_const(op->args[1]) && arg_is_const(op->args[2])) {
> uint64_t t1 = arg_info(op->args[1])->val;
> uint64_t t2 = arg_info(op->args[2])->val;
> @@ -1287,6 +1289,39 @@ static bool fold_deposit(OptContext *ctx, TCGOp *op)
> return tcg_opt_gen_movi(ctx, op, op->args[0], t1);
> }
>
> + switch (ctx->type) {
> + case TCG_TYPE_I32:
> + and_opc = INDEX_op_and_i32;
> + break;
> + case TCG_TYPE_I64:
> + and_opc = INDEX_op_and_i64;
> + break;
> + default:
> + g_assert_not_reached();
> + }
> +
> + if (arg_is_const(op->args[1])
> + && arg_info(op->args[1])->val == 0
> + && op->args[3] == 0) {
> + uint64_t mask = MAKE_64BIT_MASK(0, op->args[4]);
The docs for the TCG deposit op don't say what the restrictions on the
immediate args are, but this will be UB for QEMU if args[4] is 0.
Have we already sanitized those somewhere?
> +
> + op->opc = and_opc;
> + op->args[1] = op->args[2];
> + op->args[2] = temp_arg(tcg_constant_internal(ctx->type, mask));
> + ctx->z_mask = mask & arg_info(op->args[1])->z_mask;
> + return false;
> + }
> +
> + if (arg_is_const(op->args[2])
> + && arg_info(op->args[2])->val == 0) {
> + uint64_t mask = deposit64(-1, op->args[3], op->args[4], 0);
> +
> + op->opc = and_opc;
> + op->args[2] = temp_arg(tcg_constant_internal(ctx->type, mask));
> + ctx->z_mask = mask & arg_info(op->args[1])->z_mask;
> + return false;
> + }
> +
> ctx->z_mask = deposit64(arg_info(op->args[1])->z_mask,
> op->args[3], op->args[4],
> arg_info(op->args[2])->z_mask);
> --
thanks
-- PMM
