[PATCH, Fix PR 31098] a*C == b*C is not foldded to a == b with --fast-math/floating point

[Pranav Bhandarkar]

Hi,
> The attached patch addresses the points raised by Paolo, Kaveh and Tom. 
Hit "send" to early. Missed the ChangeLog. Here it is.

2007-10-13  Pranav Bhandarkar  <pranav.bhandarkar@celunite.com>

    * fold-const.c (fold_comparison):fold (a OP c) CMP (b OP c) -> a
    CMP b, iff c is not zero. Check the appropriate flags before doing
    this.
    * testsuite/gcc.dg/pr31098.c: New


Thanks,
Pranav

Pranav Bhandarkar
GNU Tools
Celunite, Inc.
(www.celunite.com)
+91-98220 82881



Pranav Bhandarkar wrote:
> Hi,
> The attached patch addresses the points raised by Paolo, Kaveh and Tom.
>
> Bootstrapped and regtested on i686-pc-linux-gnu.
>
> Is this ok ?
>
> cheers!
> Pranav
>
> Pranav Bhandarkar
> GNU Tools
> Celunite, Inc.
> (www.celunite.com)
> +91-98220 82881
>
>
>
> ------------------------------------------------------------------------
>
> Index: fold-const.c
> ===================================================================
> --- fold-const.c	(revision 128907)
> +++ fold-const.c	(working copy)
> @@ -9048,6 +9048,31 @@
>  	return fold_build2 (code, type, TREE_OPERAND (arg1, 0),
>  			    TREE_OPERAND (arg0, 0));
>  
> +      /* (a OP c) CMP (b OP c) -> a CMP b, iff c is not zero
> +	 if c is negative then convert into (a swap(CMP) b) */
> +      if (flag_unsafe_math_optimizations
> +	  && !HONOR_INFINITIES (TYPE_MODE (TREE_TYPE (arg0)))
> +	  && !flag_trapping_math && (TREE_CODE (arg0) == TREE_CODE (arg1))
> +	  && BINARY_CLASS_P (arg0) && !real_zerop (TREE_OPERAND (arg0,1)))
> +	{
> +	  if (TREE_CODE (TREE_OPERAND (arg0, 1)) == REAL_CST
> +	      && TREE_CODE (TREE_OPERAND (arg1, 1)) == REAL_CST )
> +	    {
> +	      REAL_VALUE_TYPE *cst0, *cst1;
> +	      cst0 = &TREE_REAL_CST (TREE_OPERAND (arg0, 1));
> +	      cst1 = &TREE_REAL_CST (TREE_OPERAND (arg1, 1));
> +	      
> +	      if (real_compare (EQ_EXPR, cst0, cst1))
> +		{
> +		  if (real_isneg (cst0))
> +		    return fold_build2 (swap_tree_comparison (code), type, TREE_OPERAND (arg0,0), TREE_OPERAND (arg1,0));
> +		  else
> +		    return fold_build2 (code, type, TREE_OPERAND (arg0,0), TREE_OPERAND (arg1,0));
> +		  
> +		}
> +	    }
> +	}
> +
>        if (TREE_CODE (arg1) == REAL_CST)
>  	{
>  	  REAL_VALUE_TYPE cst;
>   
> ------------------------------------------------------------------------
>
> --- /dev/null	2006-05-22 19:55:23.000000000 +0530
> +++ pr31098.c	2007-10-11 02:02:14.000000000 +0530
> @@ -0,0 +1,23 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-original -funsafe-math-optimizations -ffinite-math-only -fno-trapping-math" } */
> +
> +int f1(float a, float b)
> +{
> +  return a*10 == b*10;
> +}
> +
> +int f2(float a, float b)
> +{
> +  return a*10 == 10*b;
> +}
> +int f3(float a, float b)
> +{
> +  return a*-10 >= b*-10;
> +}
> +int f4(float a, float b)
> +{
> +  return a*-10 >= -10*b;
> +}
> +/* { dg-final { scan-tree-dump-times "return a == b" 2 "original" } } */
> +/* { dg-final { scan-tree-dump-times "return a <= b" 2 "original" } } */
> +/* { dg-final { cleanup-tree-dump "original" } } */
>