Re: [PATCH] Move POINTER_PLUS_EXPR folding to fold-const.c

[Richard Biener <rguenther at suse dot de>]

On Wed, 6 Aug 2014, Marek Polacek wrote:

> As discussed in the other thread, I can't just remove folding from the
> C FE and implement it on GIMPLE level, because that regressed some of
> those not-really-kosher static initializers.  Instead, fold-const.c
> has to be taught how to fold PTR0 - (PTR1 p+ A).  (Now it sounds so
> obvious.)  I added some test to that effect.  And sorry - I'm clueless
> about the PSImode targets :(.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?

Ok.

Thanks,
Richard.

> 2014-08-06  Marek Polacek  <polacek@redhat.com>
> 
> 	* fold-const.c (fold_binary_loc): Add folding of 
> 	(PTR0 - (PTR1 p+ A) -> (PTR0 - PTR1) - A.
> c/
> 	* c-typeck.c (pointer_diff): Remove P - (P + CST) optimization.
> testsuite/
> 	* gcc.dg/fold-reassoc-3.c: New test.
> 
> diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
> index 1b664bd..998e386 100644
> --- gcc/c/c-typeck.c
> +++ gcc/c/c-typeck.c
> @@ -3460,7 +3460,6 @@ pointer_diff (location_t loc, tree op0, tree op1)
>    addr_space_t as0 = TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (op0)));
>    addr_space_t as1 = TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (op1)));
>    tree target_type = TREE_TYPE (TREE_TYPE (op0));
> -  tree con0, con1, lit0, lit1;
>    tree orig_op1 = op1;
>  
>    /* If the operands point into different address spaces, we need to
> @@ -3490,7 +3489,6 @@ pointer_diff (location_t loc, tree op0, tree op1)
>    else
>      inttype = restype;
>  
> -
>    if (TREE_CODE (target_type) == VOID_TYPE)
>      pedwarn (loc, OPT_Wpointer_arith,
>  	     "pointer of type %<void *%> used in subtraction");
> @@ -3498,50 +3496,6 @@ pointer_diff (location_t loc, tree op0, tree op1)
>      pedwarn (loc, OPT_Wpointer_arith,
>  	     "pointer to a function used in subtraction");
>  
> -  /* If the conversion to ptrdiff_type does anything like widening or
> -     converting a partial to an integral mode, we get a convert_expression
> -     that is in the way to do any simplifications.
> -     (fold-const.c doesn't know that the extra bits won't be needed.
> -     split_tree uses STRIP_SIGN_NOPS, which leaves conversions to a
> -     different mode in place.)
> -     So first try to find a common term here 'by hand'; we want to cover
> -     at least the cases that occur in legal static initializers.  */
> -  if (CONVERT_EXPR_P (op0)
> -      && (TYPE_PRECISION (TREE_TYPE (op0))
> -	  == TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (op0, 0)))))
> -    con0 = TREE_OPERAND (op0, 0);
> -  else
> -    con0 = op0;
> -  if (CONVERT_EXPR_P (op1)
> -      && (TYPE_PRECISION (TREE_TYPE (op1))
> -	  == TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (op1, 0)))))
> -    con1 = TREE_OPERAND (op1, 0);
> -  else
> -    con1 = op1;
> -
> -  if (TREE_CODE (con0) == POINTER_PLUS_EXPR)
> -    {
> -      lit0 = TREE_OPERAND (con0, 1);
> -      con0 = TREE_OPERAND (con0, 0);
> -    }
> -  else
> -    lit0 = integer_zero_node;
> -
> -  if (TREE_CODE (con1) == POINTER_PLUS_EXPR)
> -    {
> -      lit1 = TREE_OPERAND (con1, 1);
> -      con1 = TREE_OPERAND (con1, 0);
> -    }
> -  else
> -    lit1 = integer_zero_node;
> -
> -  if (operand_equal_p (con0, con1, 0))
> -    {
> -      op0 = lit0;
> -      op1 = lit1;
> -    }
> -
> -
>    /* First do the subtraction as integers;
>       then drop through to build the divide operator.
>       Do not do default conversions on the minus operator
> diff --git gcc/fold-const.c gcc/fold-const.c
> index 7180662..8d66957 100644
> --- gcc/fold-const.c
> +++ gcc/fold-const.c
> @@ -10831,6 +10831,19 @@ fold_binary_loc (location_t loc,
>  	      if (tmp)
>  	        return fold_build2_loc (loc, PLUS_EXPR, type, tmp, arg01);
>  	    }
> +	  /* PTR0 - (PTR1 p+ A) -> (PTR0 - PTR1) - A, assuming PTR0 - PTR1
> +	     simplifies. */
> +	  else if (TREE_CODE (arg1) == POINTER_PLUS_EXPR)
> +	    {
> +	      tree arg10 = fold_convert_loc (loc, type,
> +					     TREE_OPERAND (arg1, 0));
> +	      tree arg11 = fold_convert_loc (loc, type,
> +					     TREE_OPERAND (arg1, 1));
> +	      tree tmp = fold_binary_loc (loc, MINUS_EXPR, type, arg0,
> +					  fold_convert_loc (loc, type, arg10));
> +	      if (tmp)
> +		return fold_build2_loc (loc, MINUS_EXPR, type, tmp, arg11);
> +	    }
>  	}
>        /* A - (-B) -> A + B */
>        if (TREE_CODE (arg1) == NEGATE_EXPR)
> diff --git gcc/testsuite/gcc.dg/fold-reassoc-3.c gcc/testsuite/gcc.dg/fold-reassoc-3.c
> index e69de29..313fb98 100644
> --- gcc/testsuite/gcc.dg/fold-reassoc-3.c
> +++ gcc/testsuite/gcc.dg/fold-reassoc-3.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-options "-fdump-tree-original" } */
> +
> +int i;
> +int *p = &i;
> +static __PTRDIFF_TYPE__ d = p - (p + 1);
> +
> +void
> +foo (void)
> +{
> +  int *q = &i;
> +  static __PTRDIFF_TYPE__ e = q - (q + 1);
> +}
> +
> +/* { dg-final { scan-tree-dump-not " - " "original" } } */
> +/* { dg-final { scan-tree-dump-not " \\\+ " "original" } } */
> +/* { dg-final { cleanup-tree-dump "orginal" } } */
> 
> 	Marek
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE / SUSE Labs
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