This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

[patch] More TRUNC_MOD_EXPR folding


 Hi,

  This patch allows signed typed TRUNC_MOD_EXPRs to be folded to AND if the
value is known to be positive.  E.g. abs(x) % 8 -> abs(x) & 7;

  Bootstrapped and regtested on ia64-linux with no new regressions, ok for
mainline?

-- 
Thanks,
Jim

http://www.csclub.uwaterloo.ca/~ja2morri/
http://phython.blogspot.com
http://open.nit.ca/wiki/?page=jim

2005-06-14  James A. Morrison  <phython@gcc.gnu.org>

	* fold_const (fold_binary): Fold X % (2**N) to X & (2**N - 1) for
	nonnegative values of X.

Index: fold-const.c
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/fold-const.c,v
retrieving revision 1.596
diff -u -p -r1.596 fold-const.c
--- fold-const.c	16 Jun 2005 18:09:31 -0000	1.596
+++ fold-const.c	16 Jun 2005 23:25:19 -0000
@@ -8337,11 +8360,11 @@ fold_binary (enum tree_code code, tree t
 	  && TREE_INT_CST_HIGH (arg1) == -1)
 	return omit_one_operand (type, integer_zero_node, arg0);
 
-      /* Optimize unsigned TRUNC_MOD_EXPR by a power of two into a
-	 BIT_AND_EXPR, i.e. "X % C" into "X & C2".  */
-      if (code == TRUNC_MOD_EXPR
-	  && TYPE_UNSIGNED (type)
-	  && integer_pow2p (arg1))
+      /* Optimize TRUNC_MOD_EXPR by a power of two into a BIT_AND_EXPR,
+         i.e. "X % C" into "X & C2", if X and C are positive.  */
+      if ((code == TRUNC_MOD_EXPR || code == FLOOR_MOD_EXPR)
+	  && (TYPE_UNSIGNED (type) || tree_expr_nonnegative_p (arg0))
+	  && integer_pow2p (arg1) && tree_int_cst_sgn (arg1) >= 0)
 	{
 	  unsigned HOST_WIDE_INT high, low;
 	  tree mask;
/* { dg-do compile } */
/* { dg-options "-fdump-tree-gimple" } */

#define ABS(x) (x > 0 ? x : -x)

unsigned int f (unsigned int a) {
	/* (unsigned)-8 is not a power of 2.  */
	return a % -8;
}

int g (int b) {
	return ABS (b) % -8;
}

int h (int c) {
	return ABS (c) % 8;
}

unsigned int k (unsigned int d) {
	return d % 8;
}

/* { dg-final { scan-tree-dump "a % 4294967288" "gimple" } } */
/* { dg-final { scan-tree-dump-times " & 7" 3 "gimple" } } */
/* { dg-final { cleanup-tree-dump "gimple" } } */

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]