Re: [Qemu-devel] [PATCH 5/5] tcg: Optimize two-address commutative operations

[Aurelien Jarno <aurelien@aurel32.net>]

On Tue, Sep 18, 2012 at 07:24:00AM -0700, Richard Henderson wrote:
> While swapping constants to the second operand, swap
> sources matching destinations to the first operand.
> 
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  tcg/optimize.c | 22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/tcg/optimize.c b/tcg/optimize.c
> index 5b0a8ce..becc408 100644
> --- a/tcg/optimize.c
> +++ b/tcg/optimize.c
> @@ -337,6 +337,8 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
>      const TCGOpDef *def;
>      TCGArg *gen_args;
>      TCGArg tmp;
> +    TCGCond cond;
> +
>      /* Array VALS has an element for each temp.
>         If this temp holds a constant then its value is kept in VALS' element.
>         If this temp is a copy of other ones then this equivalence class'
> @@ -363,7 +365,8 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
>              }
>          }
>  
> -        /* For commutative operations make constant second argument */
> +        /* For commutative operations make constant second argument, or
> +           if the destination is an input, make it the first argument.  */
>          switch (op) {
>          CASE_OP_32_64(add):
>          CASE_OP_32_64(mul):
> @@ -373,7 +376,9 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
>          CASE_OP_32_64(eqv):
>          CASE_OP_32_64(nand):
>          CASE_OP_32_64(nor):
> -            if (temps[args[1]].state == TCG_TEMP_CONST) {
> +            if (temps[args[1]].state == TCG_TEMP_CONST
> +                || (args[0] == args[2]
> +                    && temps[args[1]].state != TCG_TEMP_CONST)) {
>                  tmp = args[1];

Not directly related to movcond, and I also got that in my tree, but I
guess it's fine.

>                  args[1] = args[2];
>                  args[2] = tmp;
> @@ -398,13 +403,24 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
>              }
>              break;
>          CASE_OP_32_64(movcond):
> +            cond = args[5];
>              if (temps[args[1]].state == TCG_TEMP_CONST
>                  && temps[args[2]].state != TCG_TEMP_CONST) {
>                  tmp = args[1];
>                  args[1] = args[2];
>                  args[2] = tmp;
> -                args[5] = tcg_swap_cond(args[5]);
> +                cond = tcg_swap_cond(cond);
> +            }
> +            /* For movcond, we canonicalize the "false" input reg to match
> +               the destination reg so that the tcg backend can implement
> +               a "move if true" operation.  */
> +            if (args[0] == args[3]) {
> +                tmp = args[3];
> +                args[3] = args[4];
> +                args[4] = tmp;
> +                cond = tcg_invert_cond(cond);
>              }
> +            args[5] = cond;
>          default:
>              break;
>          }
> -- 
> 1.7.11.4
> 

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net