Re: [Qemu-devel] [RFC 18/38] tcg: add fences

["Alex Bennée" <alex.bennee@linaro.org>]

Emilio G. Cota <cota@braap.org> writes:

> Signed-off-by: Emilio G. Cota <cota@braap.org>
> ---
>  tcg/tcg-op.c  |  5 +++++
>  tcg/tcg-op.h  | 18 ++++++++++++++++++
>  tcg/tcg-opc.h |  5 +++++
>  3 files changed, 28 insertions(+)
>
> diff --git a/tcg/tcg-op.c b/tcg/tcg-op.c
> index 45098c3..6d5b1df 100644
> --- a/tcg/tcg-op.c
> +++ b/tcg/tcg-op.c
> @@ -57,6 +57,11 @@ static void tcg_emit_op(TCGContext *ctx, TCGOpcode opc, int args)
>      };
>  }
>  
> +void tcg_gen_op0(TCGContext *ctx, TCGOpcode opc)
> +{
> +    tcg_emit_op(ctx, opc, -1);

Is that -1 always safe? I'm finding the guts of the TCG opbuf a little
hard to follow but you see code like this:

        TCGOp * const op = &s->gen_op_buf[oi];
        TCGArg * const args = &s->gen_opparam_buf[op->args];

and wonder how badly that could go wrong.

> +}
> +
>  void tcg_gen_op1(TCGContext *ctx, TCGOpcode opc, TCGArg a1)
>  {
>      int pi = ctx->gen_next_parm_idx;
> diff --git a/tcg/tcg-op.h b/tcg/tcg-op.h
> index d1d763f..52482c0 100644
> --- a/tcg/tcg-op.h
> +++ b/tcg/tcg-op.h
> @@ -28,6 +28,7 @@
>  
>  /* Basic output routines.  Not for general consumption.  */
>  
> +void tcg_gen_op0(TCGContext *, TCGOpcode);
>  void tcg_gen_op1(TCGContext *, TCGOpcode, TCGArg);
>  void tcg_gen_op2(TCGContext *, TCGOpcode, TCGArg, TCGArg);
>  void tcg_gen_op3(TCGContext *, TCGOpcode, TCGArg, TCGArg, TCGArg);
> @@ -698,6 +699,23 @@ static inline void tcg_gen_trunc_i64_i32(TCGv_i32 ret, TCGv_i64 arg)
>      tcg_gen_trunc_shr_i64_i32(ret, arg, 0);
>  }
>  
> +/* fences */
> +
> +static inline void tcg_gen_fence_load(void)
> +{
> +    tcg_gen_op0(&tcg_ctx, INDEX_op_fence_load);
> +}
> +
> +static inline void tcg_gen_fence_store(void)
> +{
> +    tcg_gen_op0(&tcg_ctx, INDEX_op_fence_store);
> +}
> +
> +static inline void tcg_gen_fence_full(void)
> +{
> +    tcg_gen_op0(&tcg_ctx, INDEX_op_fence_full);
> +}
> +
>  /* QEMU specific operations.  */
>  
>  #ifndef TARGET_LONG_BITS
> diff --git a/tcg/tcg-opc.h b/tcg/tcg-opc.h
> index 13ccb60..85de953 100644
> --- a/tcg/tcg-opc.h
> +++ b/tcg/tcg-opc.h
> @@ -167,6 +167,11 @@ DEF(muls2_i64, 2, 2, 0, IMPL64 | IMPL(TCG_TARGET_HAS_muls2_i64))
>  DEF(muluh_i64, 1, 2, 0, IMPL(TCG_TARGET_HAS_muluh_i64))
>  DEF(mulsh_i64, 1, 2, 0, IMPL(TCG_TARGET_HAS_mulsh_i64))
>  
> +/* fences */
> +DEF(fence_load, 0, 0, 0, 0)
> +DEF(fence_store, 0, 0, 0, 0)
> +DEF(fence_full, 0, 0, 0, 0)
> +
>  /* QEMU specific */
>  #if TARGET_LONG_BITS > TCG_TARGET_REG_BITS
>  DEF(debug_insn_start, 0, 0, 2, TCG_OPF_NOT_PRESENT)

-- 
Alex Bennée