Re: [PATCH 28/28] tcg/riscv: Remove MO_BSWAP handling

[Alistair Francis]

On Mon, Jun 14, 2021 at 6:54 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> TCG_TARGET_HAS_MEMORY_BSWAP is already unset for this backend,
> which means that MO_BSWAP be handled by the middle-end and
> will never be seen by the backend.  Thus the indexes used with
> qemu_{ld,st}_helpers will always be zero.
>
> Tidy the comments and asserts in tcg_out_qemu_{ld,st}_direct.
> It is not that we do not handle bswap "yet", but never will.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Acked-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  tcg/riscv/tcg-target.c.inc | 64 ++++++++++++++++++++------------------
>  1 file changed, 33 insertions(+), 31 deletions(-)
>
> diff --git a/tcg/riscv/tcg-target.c.inc b/tcg/riscv/tcg-target.c.inc
> index da7eecafc5..c16f96b401 100644
> --- a/tcg/riscv/tcg-target.c.inc
> +++ b/tcg/riscv/tcg-target.c.inc
> @@ -852,37 +852,43 @@ static void tcg_out_mb(TCGContext *s, TCGArg a0)
>  /* helper signature: helper_ret_ld_mmu(CPUState *env, target_ulong addr,
>   *                                     TCGMemOpIdx oi, uintptr_t ra)
>   */
> -static void * const qemu_ld_helpers[16] = {
> -    [MO_UB]   = helper_ret_ldub_mmu,
> -    [MO_SB]   = helper_ret_ldsb_mmu,
> -    [MO_LEUW] = helper_le_lduw_mmu,
> -    [MO_LESW] = helper_le_ldsw_mmu,
> -    [MO_LEUL] = helper_le_ldul_mmu,
> +static void * const qemu_ld_helpers[8] = {
> +    [MO_UB] = helper_ret_ldub_mmu,
> +    [MO_SB] = helper_ret_ldsb_mmu,
> +#ifdef HOST_WORDS_BIGENDIAN
> +    [MO_UW] = helper_be_lduw_mmu,
> +    [MO_SW] = helper_be_ldsw_mmu,
> +    [MO_UL] = helper_be_ldul_mmu,
>  #if TCG_TARGET_REG_BITS == 64
> -    [MO_LESL] = helper_le_ldsl_mmu,
> +    [MO_SL] = helper_be_ldsl_mmu,
>  #endif
> -    [MO_LEQ]  = helper_le_ldq_mmu,
> -    [MO_BEUW] = helper_be_lduw_mmu,
> -    [MO_BESW] = helper_be_ldsw_mmu,
> -    [MO_BEUL] = helper_be_ldul_mmu,
> +    [MO_Q]  = helper_be_ldq_mmu,
> +#else
> +    [MO_UW] = helper_le_lduw_mmu,
> +    [MO_SW] = helper_le_ldsw_mmu,
> +    [MO_UL] = helper_le_ldul_mmu,
>  #if TCG_TARGET_REG_BITS == 64
> -    [MO_BESL] = helper_be_ldsl_mmu,
> +    [MO_SL] = helper_le_ldsl_mmu,
> +#endif
> +    [MO_Q]  = helper_le_ldq_mmu,
>  #endif
> -    [MO_BEQ]  = helper_be_ldq_mmu,
>  };
>
>  /* helper signature: helper_ret_st_mmu(CPUState *env, target_ulong addr,
>   *                                     uintxx_t val, TCGMemOpIdx oi,
>   *                                     uintptr_t ra)
>   */
> -static void * const qemu_st_helpers[16] = {
> -    [MO_UB]   = helper_ret_stb_mmu,
> -    [MO_LEUW] = helper_le_stw_mmu,
> -    [MO_LEUL] = helper_le_stl_mmu,
> -    [MO_LEQ]  = helper_le_stq_mmu,
> -    [MO_BEUW] = helper_be_stw_mmu,
> -    [MO_BEUL] = helper_be_stl_mmu,
> -    [MO_BEQ]  = helper_be_stq_mmu,
> +static void * const qemu_st_helpers[4] = {
> +    [MO_8]   = helper_ret_stb_mmu,
> +#ifdef HOST_WORDS_BIGENDIAN
> +    [MO_16] = helper_be_stw_mmu,
> +    [MO_32] = helper_be_stl_mmu,
> +    [MO_64] = helper_be_stq_mmu,
> +#else
> +    [MO_16] = helper_le_stw_mmu,
> +    [MO_32] = helper_le_stl_mmu,
> +    [MO_64] = helper_le_stq_mmu,
> +#endif
>  };
>
>  /* We don't support oversize guests */
> @@ -997,7 +1003,7 @@ static bool tcg_out_qemu_ld_slow_path(TCGContext *s, 
> TCGLabelQemuLdst *l)
>      tcg_out_movi(s, TCG_TYPE_PTR, a2, oi);
>      tcg_out_movi(s, TCG_TYPE_PTR, a3, (tcg_target_long)l->raddr);
>
> -    tcg_out_call(s, qemu_ld_helpers[opc & (MO_BSWAP | MO_SSIZE)]);
> +    tcg_out_call(s, qemu_ld_helpers[opc & MO_SSIZE]);
>      tcg_out_mov(s, (opc & MO_SIZE) == MO_64, l->datalo_reg, a0);
>
>      tcg_out_goto(s, l->raddr);
> @@ -1042,7 +1048,7 @@ static bool tcg_out_qemu_st_slow_path(TCGContext *s, 
> TCGLabelQemuLdst *l)
>      tcg_out_movi(s, TCG_TYPE_PTR, a3, oi);
>      tcg_out_movi(s, TCG_TYPE_PTR, a4, (tcg_target_long)l->raddr);
>
> -    tcg_out_call(s, qemu_st_helpers[opc & (MO_BSWAP | MO_SSIZE)]);
> +    tcg_out_call(s, qemu_st_helpers[opc & MO_SIZE]);
>
>      tcg_out_goto(s, l->raddr);
>      return true;
> @@ -1052,10 +1058,8 @@ static bool tcg_out_qemu_st_slow_path(TCGContext *s, 
> TCGLabelQemuLdst *l)
>  static void tcg_out_qemu_ld_direct(TCGContext *s, TCGReg lo, TCGReg hi,
>                                     TCGReg base, MemOp opc, bool is_64)
>  {
> -    const MemOp bswap = opc & MO_BSWAP;
> -
> -    /* We don't yet handle byteswapping, assert */
> -    g_assert(!bswap);
> +    /* Byte swapping is left to middle-end expansion. */
> +    tcg_debug_assert((opc & MO_BSWAP) == 0);
>
>      switch (opc & (MO_SSIZE)) {
>      case MO_UB:
> @@ -1139,10 +1143,8 @@ static void tcg_out_qemu_ld(TCGContext *s, const 
> TCGArg *args, bool is_64)
>  static void tcg_out_qemu_st_direct(TCGContext *s, TCGReg lo, TCGReg hi,
>                                     TCGReg base, MemOp opc)
>  {
> -    const MemOp bswap = opc & MO_BSWAP;
> -
> -    /* We don't yet handle byteswapping, assert */
> -    g_assert(!bswap);
> +    /* Byte swapping is left to middle-end expansion. */
> +    tcg_debug_assert((opc & MO_BSWAP) == 0);
>
>      switch (opc & (MO_SSIZE)) {
>      case MO_8:
> --
> 2.25.1
>
>