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[patch] Fold some comparisons of bit operations
- From: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- To: gcc-patches at gcc dot gnu dot org
- Date: Mon, 21 Jul 2003 21:09:18 +0200
- Subject: [patch] Fold some comparisons of bit operations
Hello,
this patch adds two transformations to fold (descriptions see in
comments in patches).
Zdenek
Changelog:
* fold-const.c (fold): Fold some comparisons of bit operations.
Index: fold-const.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fold-const.c,v
retrieving revision 1.226.2.8
diff -c -3 -p -r1.226.2.8 fold-const.c
*** fold-const.c 3 Jul 2003 16:33:20 -0000 1.226.2.8
--- fold-const.c 21 Jul 2003 18:27:33 -0000
*************** fold (expr)
*** 6504,6509 ****
--- 6504,6537 ----
}
}
+ /* If we have (A & C) == D where D & ~C != 0, convert this into 0.
+ Similarly for NE_EXPR. */
+ if ((code == EQ_EXPR || code == NE_EXPR)
+ && TREE_CODE (arg0) == BIT_AND_EXPR
+ && TREE_CODE (arg1) == INTEGER_CST
+ && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST)
+ {
+ tree dandnotc = fold (build (BIT_ANDTC_EXPR, TREE_TYPE (arg0),
+ arg1, TREE_OPERAND (arg0, 1)));
+ tree rslt = code == EQ_EXPR ? integer_zero_node : integer_one_node;
+ if (!integer_zerop (dandnotc))
+ return omit_one_operand (type, rslt, arg0);
+ }
+
+ /* If we have (A | C) == D where C & ~D != 0, convert this into 0.
+ Similarly for NE_EXPR. */
+ if ((code == EQ_EXPR || code == NE_EXPR)
+ && TREE_CODE (arg0) == BIT_IOR_EXPR
+ && TREE_CODE (arg1) == INTEGER_CST
+ && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST)
+ {
+ tree candnotd = fold (build (BIT_ANDTC_EXPR, TREE_TYPE (arg0),
+ TREE_OPERAND (arg0, 1), arg1));
+ tree rslt = code == EQ_EXPR ? integer_zero_node : integer_one_node;
+ if (!integer_zerop (candnotd))
+ return omit_one_operand (type, rslt, arg0);
+ }
+
/* If X is unsigned, convert X < (1 << Y) into X >> Y == 0
and similarly for >= into !=. */
if ((code == LT_EXPR || code == GE_EXPR)