Richard Guenther - [PATCH] Fix PR30951, missed folding of x == x + 1 (original) (raw)

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• From: Richard Guenther
• To: gcc-patches at gcc dot gnu dot org
• Date: Sat, 24 Feb 2007 20:55:14 +0100 (CET)
• Subject: [PATCH] Fix PR30951, missed folding of x == x + 1

This fixes PR30951 which I noticed while working on the fix for 30364. We can fold == and != comparisons regardless of overflow behavior for X +- CST op X.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to mainline.

Richard.

2007-02-24 Richard Guenther rguenther@suse.de

PR middle-end/30951
* fold-const.c (fold_binary): Fold x +- CST op x for
EQ_EXPR and NE_EXPR.

* gcc.dg/pr30951.c: New testcase.

Index: fold-const.c

*** fold-const.c (revision 122288) --- fold-const.c (working copy) *************** fold_binary (enum tree_code code, tree t *** 11203,11208 **** --- 11207,11230 ---- fold_convert (TREE_TYPE (arg0), arg1), TREE_OPERAND (arg0, 1)));
+ /* Transform comparisons of the form X +- C CMP X. / + if ((TREE_CODE (arg0) == PLUS_EXPR || TREE_CODE (arg0) == MINUS_EXPR) + && operand_equal_p (TREE_OPERAND (arg0, 0), arg1, 0) + && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST + && (INTEGRAL_TYPE_P (TREE_TYPE (arg0)) + || POINTER_TYPE_P (TREE_TYPE (arg0)))) + { + tree cst = TREE_OPERAND (arg0, 1); + + if (code == EQ_EXPR + && !integer_zerop (cst)) + return omit_two_operands (type, boolean_false_node, + TREE_OPERAND (arg0, 0), arg1); + else + return omit_two_operands (type, boolean_true_node, + TREE_OPERAND (arg0, 0), arg1); + } + / If we have X - Y == 0, we can convert that to X == Y and similarly for !=. Don't do this for ordered comparisons due to overflow. */ if (TREE_CODE (arg0) == MINUS_EXPR Index: testsuite/gcc.dg/pr30951.c

*** testsuite/gcc.dg/pr30951.c (revision 0) --- testsuite/gcc.dg/pr30951.c (revision 0)

*** 0 **** --- 1,36 ----

• /* { dg-do link } */
• extern void link_error (void);
• void test (int x, unsigned int y)
• {
• if (x + 5 == x)

• link_error ();

• if (x == x + 10)

• link_error ();

• if (y + 5 == y)

• link_error ();

• if (y == y + 10)

• link_error ();

• if (x + 5 != x)

• ;

• else

• link_error ();

• if (x != x + 10)

• ;

• else

• link_error ();

• if (y + 5 != y)

• ;

• else

• link_error ();

• if (y != y + 10)

• ;

• else

• link_error ();

• }
• int main()
• {
• return 0;
• }

• Follow-Ups:
  • Re: [PATCH] Fix PR30951, missed folding of x == x + 1
    * From: Joseph S. Myers