Re: [Qemu-devel] [PATCH 25/32] ppc: Handle unconditional (always/never) traps at translation time

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Jul 27, 2016 at 08:21:19AM +1000, Benjamin Herrenschmidt wrote:
> We don't need to call a helper for trap always and trap never
> which are used by Linux under some circumstances.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> ---
>  target-ppc/translate.c | 48 ++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 42 insertions(+), 6 deletions(-)
> 
> diff --git a/target-ppc/translate.c b/target-ppc/translate.c
> index 9af3f5f..57a891b 100644
> --- a/target-ppc/translate.c
> +++ b/target-ppc/translate.c
> @@ -3360,10 +3360,29 @@ static void gen_sc(DisasContext *ctx)
>  
>  /***                                Trap                                   ***/
>  
> +/* Check for unconditional traps (always or never) */
> +static bool check_unconditional_trap(DisasContext *ctx)
> +{
> +    /* Trap never */
> +    if (TO(ctx->opcode) == 0) {
> +        return true;
> +    }
> +    /* Trap always */
> +    if (TO(ctx->opcode) == 31) {
> +        gen_exception_err(ctx, POWERPC_EXCP_PROGRAM, POWERPC_EXCP_TRAP);

Should you be returning true here?

Without it, IIUC, the functions below will generate the unconditional
trap, then generate more code to actually test the condition and trap
again.

> +    }
> +    return false;
> +}
> +
>  /* tw */
>  static void gen_tw(DisasContext *ctx)
>  {
> -    TCGv_i32 t0 = tcg_const_i32(TO(ctx->opcode));
> +    TCGv_i32 t0;
> +
> +    if (check_unconditional_trap(ctx)) {
> +        return;
> +    }
> +    t0 = tcg_const_i32(TO(ctx->opcode));
>      gen_helper_tw(cpu_env, cpu_gpr[rA(ctx->opcode)], cpu_gpr[rB(ctx->opcode)],
>                    t0);
>      tcg_temp_free_i32(t0);
> @@ -3372,8 +3391,14 @@ static void gen_tw(DisasContext *ctx)
>  /* twi */
>  static void gen_twi(DisasContext *ctx)
>  {
> -    TCGv t0 = tcg_const_tl(SIMM(ctx->opcode));
> -    TCGv_i32 t1 = tcg_const_i32(TO(ctx->opcode));
> +    TCGv t0;
> +    TCGv_i32 t1;
> +
> +    if (check_unconditional_trap(ctx)) {
> +        return;
> +    }
> +    t0 = tcg_const_tl(SIMM(ctx->opcode));
> +    t1 = tcg_const_i32(TO(ctx->opcode));
>      gen_helper_tw(cpu_env, cpu_gpr[rA(ctx->opcode)], t0, t1);
>      tcg_temp_free(t0);
>      tcg_temp_free_i32(t1);
> @@ -3383,7 +3408,12 @@ static void gen_twi(DisasContext *ctx)
>  /* td */
>  static void gen_td(DisasContext *ctx)
>  {
> -    TCGv_i32 t0 = tcg_const_i32(TO(ctx->opcode));
> +    TCGv_i32 t0;
> +
> +    if (check_unconditional_trap(ctx)) {
> +        return;
> +    }
> +    t0 = tcg_const_i32(TO(ctx->opcode));
>      gen_helper_td(cpu_env, cpu_gpr[rA(ctx->opcode)], cpu_gpr[rB(ctx->opcode)],
>                    t0);
>      tcg_temp_free_i32(t0);
> @@ -3392,8 +3422,14 @@ static void gen_td(DisasContext *ctx)
>  /* tdi */
>  static void gen_tdi(DisasContext *ctx)
>  {
> -    TCGv t0 = tcg_const_tl(SIMM(ctx->opcode));
> -    TCGv_i32 t1 = tcg_const_i32(TO(ctx->opcode));
> +    TCGv t0;
> +    TCGv_i32 t1;
> +
> +    if (check_unconditional_trap(ctx)) {
> +        return;
> +    }
> +    t0 = tcg_const_tl(SIMM(ctx->opcode));
> +    t1 = tcg_const_i32(TO(ctx->opcode));
>      gen_helper_td(cpu_env, cpu_gpr[rA(ctx->opcode)], t0, t1);
>      tcg_temp_free(t0);
>      tcg_temp_free_i32(t1);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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