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fold-const.c (pointer_may_wrap_p): New static function. 

* fold-const.c (pointer_may_wrap_p): New static function.
	(fold_comparison): Add another test for pointer overflow.  Use
	pointer_may_wrap_p to disable some false positives.

From-SVN: r134440
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Ian Lance Taylor 2008-04-18 15:22:40 +00:00 committed by Ian Lance Taylor
parent b6baa67d79
commit 6e3c5c30e8
2 changed files with 87 additions and 4 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2008-04-18 Ian Lance Taylor <iant@google.com>
* fold-const.c (pointer_may_wrap_p): New static function.
(fold_comparison): Add another test for pointer overflow. Use
pointer_may_wrap_p to disable some false positives.
2008-04-18 Kris Van Hees <kris.van.hees@oracle.com>
* c-common.c (CHAR16_TYPE, CHAR32_TYPE): New macros.

81
gcc/fold-const.c
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@ -8394,6 +8394,66 @@ maybe_canonicalize_comparison (enum tree_code code, tree type,
return t;
}
/* Return whether BASE + OFFSET + BITPOS may wrap around the address
space. This is used to avoid issuing overflow warnings for
expressions like &p->x which can not wrap. */
static bool
pointer_may_wrap_p (tree base, tree offset, HOST_WIDE_INT bitpos)
{
tree size;
unsigned HOST_WIDE_INT offset_low, total_low;
HOST_WIDE_INT offset_high, total_high;
if (!POINTER_TYPE_P (TREE_TYPE (base)))
return true;
if (bitpos < 0)
return true;
size = size_in_bytes (TREE_TYPE (TREE_TYPE (base)));
if (size == NULL_TREE || TREE_CODE (size) != INTEGER_CST)
return true;
/* We can do slightly better for SIZE if we have an ADDR_EXPR of an
array. */
if (TREE_CODE (base) == ADDR_EXPR)
{
tree base_size = size_in_bytes (TREE_TYPE (TREE_OPERAND (base, 0)));
if (base_size != NULL_TREE
&& TREE_CODE (base_size) == INTEGER_CST
&& INT_CST_LT_UNSIGNED (size, base_size))
size = base_size;
}
if (offset == NULL_TREE)
{
offset_low = 0;
offset_high = 0;
}
else if (TREE_CODE (offset) != INTEGER_CST || TREE_OVERFLOW (offset))
return true;
else
{
offset_low = TREE_INT_CST_LOW (offset);
offset_high = TREE_INT_CST_HIGH (offset);
}
if (add_double_with_sign (offset_low, offset_high,
bitpos / BITS_PER_UNIT, 0,
&total_low, &total_high,
true))
return true;
if ((unsigned HOST_WIDE_INT) total_high
< (unsigned HOST_WIDE_INT) TREE_INT_CST_HIGH (size))
return false;
if ((unsigned HOST_WIDE_INT) total_high
> (unsigned HOST_WIDE_INT) TREE_INT_CST_HIGH (size))
return true;
return total_low > TREE_INT_CST_LOW (size);
}
/* Subroutine of fold_binary. This routine performs all of the
transformations that are common to the equality/inequality
operators (EQ_EXPR and NE_EXPR) and the ordering operators
@ -8544,10 +8604,24 @@ fold_comparison (enum tree_code code, tree type, tree op0, tree op1)
{
/* We can fold this expression to a constant if the non-constant
offset parts are equal. */
if (offset0 == offset1
if ((offset0 == offset1
|| (offset0 && offset1
&& operand_equal_p (offset0, offset1, 0)))
&& (code == EQ_EXPR
|| code == NE_EXPR
|| POINTER_TYPE_OVERFLOW_UNDEFINED))
{
if (code != EQ_EXPR
&& code != NE_EXPR
&& bitpos0 != bitpos1
&& (pointer_may_wrap_p (base0, offset0, bitpos0)
|| pointer_may_wrap_p (base1, offset1, bitpos1)))
fold_overflow_warning (("assuming pointer wraparound does not "
"occur when comparing P +- C1 with "
"P +- C2"),
WARN_STRICT_OVERFLOW_CONDITIONAL);
switch (code)
{
case EQ_EXPR:
@ -8593,7 +8667,10 @@ fold_comparison (enum tree_code code, tree type, tree op0, tree op1)
else
offset1 = fold_convert (signed_size_type_node, offset1);
if (code != EQ_EXPR && code != NE_EXPR)
if (code != EQ_EXPR
&& code != NE_EXPR
&& (pointer_may_wrap_p (base0, offset0, bitpos0)
|| pointer_may_wrap_p (base1, offset1, bitpos1)))
fold_overflow_warning (("assuming pointer wraparound does not "
"occur when comparing P +- C1 with "
"P +- C2"),