Re: Extend widening_mul pass to handle fixed-point types

[Richard Sandiford <rdsandiford@googlemail.com>]

Richard Sandiford <rdsandiford@googlemail.com> writes:
> Ramana Radhakrishnan <ramana.radhakrishnan@arm.com> writes:
>> Hmmm there are regressions after my patch was applied. I had to do some
>> rebuilds because trunk appears to be broken for other reasons at the
>> minute for ARM which I shall investigate next. 
>
> Yeah, I think it's the other way about: expand_widen_pattern_expr
> is using the right type and convert_plusminus_to_widen is using
> the wrong one.  The type we pass to optab_for_tree_code determines
> the _sign_ of the multiplication, not the size, so we want to pass
> in the unwidened type.
>
>> We weren't generating any widening operations before this patch (and I
>> suspect my 2 patches are just for fixing the ICE's and doing the right
>> thing). If it were just adding support for fixed point arithmetic then
>> this is just broken because it shouldn't have changed the way in  which
>> code was generated for normal integer operations.  
>
> For the record, the patch wasn't just about adding fixed-point support.
> It was also about allowing multiply-accumulate to be used where no plain
> multiplication exists.  So the problem for ARM was that the use of the
> wrong type in convert_plusminus_to_widen was being hidden by the use of
> the right type in convert_mult_widen (i.e. the patch exposed a latent bug).
>
> Could you give the attached patch a try?  It also fixes a case where
> the code could create mixed sign-and-unsigned maccs (a bug that existed
> before my patch) and a botched call to is_widening_mult_p (a bug
> introduced by my patch, sorry).

Now bootstrapped & regression-tested on x86_64-linux-gnu.  Ramana
also confirms that it fixes the ICEs and incorrect arith-rand-ll.c
code on ARM.  OK to install?

Richard

> gcc/
> 	* tree-ssa-math-opts.c (convert_plusminus_to_widen): Fix type
> 	used in the call to optab_for_tree_code.  Fix the second
> 	is_widening_mult_p call.  Check that both unwidened operands
> 	have the same sign.
>
> Index: gcc/tree-ssa-math-opts.c
> ===================================================================
> --- gcc/tree-ssa-math-opts.c	2010-07-28 21:09:59.000000000 +0100
> +++ gcc/tree-ssa-math-opts.c	2010-07-28 21:10:00.000000000 +0100
> @@ -1414,13 +1414,6 @@ convert_plusminus_to_widen (gimple_stmt_
>    else
>      wmult_code = WIDEN_MULT_PLUS_EXPR;
>  
> -  /* Verify that the machine can perform a widening multiply
> -     accumulate in this mode/signedness combination, otherwise
> -     this transformation is likely to pessimize code.  */
> -  this_optab = optab_for_tree_code (wmult_code, type, optab_default);
> -  if (optab_handler (this_optab, TYPE_MODE (type)) == CODE_FOR_nothing)
> -    return false;
> -
>    rhs1 = gimple_assign_rhs1 (stmt);
>    rhs2 = gimple_assign_rhs2 (stmt);
>  
> @@ -1447,37 +1440,49 @@ convert_plusminus_to_widen (gimple_stmt_
>        if (!is_widening_mult_p (rhs1_stmt, &type1, &mult_rhs1,
>  			       &type2, &mult_rhs2))
>  	return false;
> -      mult_rhs1 = fold_convert (type1, mult_rhs1);
> -      mult_rhs2 = fold_convert (type2, mult_rhs2);
>        add_rhs = rhs2;
>      }
>    else if (rhs2_code == MULT_EXPR)
>      {
> -      if (!is_widening_mult_p (rhs1_stmt, &type1, &mult_rhs1,
> +      if (!is_widening_mult_p (rhs2_stmt, &type1, &mult_rhs1,
>  			       &type2, &mult_rhs2))
>  	return false;
> -      mult_rhs1 = fold_convert (type1, mult_rhs1);
> -      mult_rhs2 = fold_convert (type2, mult_rhs2);
>        add_rhs = rhs1;
>      }
>    else if (code == PLUS_EXPR && rhs1_code == WIDEN_MULT_EXPR)
>      {
>        mult_rhs1 = gimple_assign_rhs1 (rhs1_stmt);
>        mult_rhs2 = gimple_assign_rhs2 (rhs1_stmt);
> +      type1 = TREE_TYPE (mult_rhs1);
> +      type2 = TREE_TYPE (mult_rhs2);
>        add_rhs = rhs2;
>      }
>    else if (rhs2_code == WIDEN_MULT_EXPR)
>      {
>        mult_rhs1 = gimple_assign_rhs1 (rhs2_stmt);
>        mult_rhs2 = gimple_assign_rhs2 (rhs2_stmt);
> +      type1 = TREE_TYPE (mult_rhs1);
> +      type2 = TREE_TYPE (mult_rhs2);
>        add_rhs = rhs1;
>      }
>    else
>      return false;
>  
> +  if (TYPE_UNSIGNED (type1) != TYPE_UNSIGNED (type2))
> +    return false;
> +
> +  /* Verify that the machine can perform a widening multiply
> +     accumulate in this mode/signedness combination, otherwise
> +     this transformation is likely to pessimize code.  */
> +  this_optab = optab_for_tree_code (wmult_code, type1, optab_default);
> +  if (optab_handler (this_optab, TYPE_MODE (type)) == CODE_FOR_nothing)
> +    return false;
> +
>    /* ??? May need some type verification here?  */
>  
> -  gimple_assign_set_rhs_with_ops_1 (gsi, wmult_code, mult_rhs1, mult_rhs2,
> +  gimple_assign_set_rhs_with_ops_1 (gsi, wmult_code,
> +				    fold_convert (type1, mult_rhs1),
> +				    fold_convert (type2, mult_rhs2),
>  				    add_rhs);
>    update_stmt (gsi_stmt (*gsi));
>    return true;