Re: [PATCH 1/6] target/ppc: add byte-reverse br[dwh] instructions

[Richard Henderson <richard.henderson@linaro.org>]

On 6/12/20 9:20 PM, Lijun Pan wrote:
> POWER ISA 3.1 introduces following byte-reverse instructions:
> brd: Byte-Reverse Doubleword X-form
> brw: Byte-Reverse Word X-form
> brh: Byte-Reverse Halfword X-form
> 
> Signed-off-by: Lijun Pan <ljp@linux.ibm.com>
> ---
>  target/ppc/translate.c | 62 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 62 insertions(+)
> 
> diff --git a/target/ppc/translate.c b/target/ppc/translate.c
> index 4ce3d664b5..2d48fbc8db 100644
> --- a/target/ppc/translate.c
> +++ b/target/ppc/translate.c
> @@ -6971,7 +6971,69 @@ static void gen_dform3D(DisasContext *ctx)
>      return gen_invalid(ctx);
>  }
>  
> +/* brd */
> +static void gen_brd(DisasContext *ctx)
> +{
> +	TCGv_i64 temp = tcg_temp_new_i64();
> +
> +	tcg_gen_bswap64_i64(temp, cpu_gpr[rS(ctx->opcode)]);
> +	tcg_gen_st_i64(temp, cpu_env, offsetof(CPUPPCState, gpr[rA(ctx->opcode)]));


The store is wrong.  You cannot modify storage behind a tcg global variable
like that.  This should just be

    tcg_gen_bswap64_i64(cpu_gpr[rA(ctx->opcode)],
                        cpu_gpr[rS(ctx->opcode)]);

Is this code is within an ifdef for TARGET_PPC64?
If not, then this will break the 32-bit qemu-system-ppc build.
Are you sure you have built and tested all configurations?


> +/* brw */
> +static void gen_brw(DisasContext *ctx)
> +{
> +	TCGv_i64 temp = tcg_temp_new_i64();
> +	TCGv_i64 lsb = tcg_temp_new_i64();
> +	TCGv_i64 msb = tcg_temp_new_i64();
> +
> +	tcg_gen_movi_i64(lsb, 0x00000000ffffffffull);
> +	tcg_gen_and_i64(temp, lsb, cpu_gpr[rS(ctx->opcode)]);
> +	tcg_gen_bswap32_i64(lsb, temp);
> +	
> +	tcg_gen_shri_i64(msb, cpu_gpr[rS(ctx->opcode)], 32);
> +	tcg_gen_bswap32_i64(temp, msb);
> +	tcg_gen_shli_i64(msb, temp, 32);
> +	
> +	tcg_gen_or_i64(temp, lsb, msb);
> +
> +	tcg_gen_st_i64(temp, cpu_env, offsetof(CPUPPCState, gpr[rA(ctx->opcode)]));

Again, the store is wrong.

In addition, this can be computed as

    tcg_gen_bswap64_i64(dest, source);
    tcg_gen_rotli_i64(dest, dest, 32);

> +static void gen_brh(DisasContext *ctx)
> +{
> +	TCGv_i64 temp = tcg_temp_new_i64();
> +	TCGv_i64 t0 = tcg_temp_new_i64();
> +	TCGv_i64 t1 = tcg_temp_new_i64();
> +	TCGv_i64 t2 = tcg_temp_new_i64();
> +	TCGv_i64 t3 = tcg_temp_new_i64();
> +
> +	tcg_gen_movi_i64(t0, 0x00ff00ff00ff00ffull);
> +	tcg_gen_shri_i64(t1, cpu_gpr[rS(ctx->opcode)], 8);
> +	tcg_gen_and_i64(t2, t1, t0);
> +	tcg_gen_and_i64(t1, cpu_gpr[rS(ctx->opcode)], t0);
> +	tcg_gen_shli_i64(t1, t1, 8);
> +	tcg_gen_or_i64(temp, t1, t2);
> +	tcg_gen_st_i64(temp, cpu_env, offsetof(CPUPPCState, gpr[rA(ctx->opcode)]));

Again, the store is wrong.


r~