[PATCH][i386] Fix scalar costing in ix86_add_stmt_cost

[Jan Hubicka]

> 
> The following fixes bogus differences in scalar iteration cost
> computed by the vectorizer when comparing 128 and 256 bit vectorizations.
> This was caused by the hook looking at the vector types mode even
> for kind == scalar_stmt and thus returning vector operation costs
> for things like add or negate.
> 
> This is most noticable on targets where ix86_vec_cost applies
> multiplication based on vector size (TARGET_AVX128_OPTIMAL, thus
> Zen and Bulldozer).  But it will also adjust the actual costs
> everywhere where scalar and vector costs diverge.
> 
> The adjustments done for Silvermont also look broken since they
> are applied to both scalar and vector cost which makes it mostly
> a no-op.  The patch adjusts it to only apply for vector costing
> but of course I didn't benchmark this and the magic number of 1.7
> may not make sense after this fix so I'm happy to leave that
> out - Kirill?  Should I just go ahead with that for trunk (we can
> revert or adjust if autotesters pick up regressions on your side)?
> 
> Bootstrap & regtest running on x86_64-unknown-linux-gnu, OK?
> 
> Richard.
> 
> 2018-10-04   Richard Biener  <rguenther@suse.de>
> 
> 	* config/i386/i386.c (ix86_add_stmt_cost): When scalar cost
> 	is asked for initialize mode to the component mode of the
> 	vector type.  Make sure Bonnel and esp. other Atom cost
> 	adjustments are not done for scalar cost estimates.
OK,
thanks!
> 
> Index: gcc/config/i386/i386.c
> ===================================================================
> --- gcc/config/i386/i386.c	(revision 264837)
> +++ gcc/config/i386/i386.c	(working copy)
> @@ -49486,17 +49486,21 @@ ix86_add_stmt_cost (void *data, int coun
>  {
>    unsigned *cost = (unsigned *) data;
>    unsigned retval = 0;
> +  bool scalar_p
> +    = (kind == scalar_stmt || kind == scalar_load || kind == scalar_store);
>  
>    tree vectype = stmt_info ? stmt_vectype (stmt_info) : NULL_TREE;
>    int stmt_cost = - 1;
>  
>    bool fp = false;
> -  machine_mode mode = TImode;
> +  machine_mode mode = scalar_p ? SImode : TImode;
>  
>    if (vectype != NULL)
>      {
>        fp = FLOAT_TYPE_P (vectype);
>        mode = TYPE_MODE (vectype);
> +      if (scalar_p)
> +	mode = TYPE_MODE (TREE_TYPE (vectype));
>      }
>  
>    if ((kind == vector_stmt || kind == scalar_stmt)
> @@ -49632,7 +49636,7 @@ ix86_add_stmt_cost (void *data, int coun
>      stmt_cost = ix86_builtin_vectorization_cost (kind, vectype, misalign);
>  
>    /* Penalize DFmode vector operations for Bonnell.  */
> -  if (TARGET_BONNELL && kind == vector_stmt
> +  if (TARGET_BONNELL && !scalar_p
>        && vectype && GET_MODE_INNER (TYPE_MODE (vectype)) == DFmode)
>      stmt_cost *= 5;  /* FIXME: The value here is arbitrary.  */
>  
> @@ -49648,7 +49652,8 @@ ix86_add_stmt_cost (void *data, int coun
>       for Silvermont as it has out of order integer pipeline and can execute
>       2 scalar instruction per tick, but has in order SIMD pipeline.  */
>    if ((TARGET_SILVERMONT || TARGET_GOLDMONT || TARGET_GOLDMONT_PLUS
> -       || TARGET_TREMONT || TARGET_INTEL) && stmt_info && stmt_info->stmt)
> +       || TARGET_TREMONT || TARGET_INTEL)
> +      && !scalar_p && stmt_info && stmt_info->stmt)
>      {
>        tree lhs_op = gimple_get_lhs (stmt_info->stmt);
>        if (lhs_op && TREE_CODE (TREE_TYPE (lhs_op)) == INTEGER_TYPE)