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re PR middle-end/5877 (negative offset to array index leads to inefficient code) 

PR middle-end/5877
	* expr.c (highest_pow2_factor): Check TREE_INT_CST_LOW
	even for non-representable constants.

From-SVN: r50495
This commit is contained in:
Jakub Jelinek 2002-03-09 14:23:44 +01:00 committed by Jakub Jelinek
parent 93fe8e9229
commit e0f1be5c98
2 changed files with 18 additions and 11 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2002-03-09 Jakub Jelinek <jakub@redhat.com>
PR middle-end/5877
* expr.c (highest_pow2_factor): Check TREE_INT_CST_LOW
even for non-representable constants.
Sat Mar 9 07:20:01 2002 Richard Kenner <kenner@vlsi1.ultra.nyu.edu>
* emit-rtl.c (copy_most_rtx): Accept EXPR_LIST for may_share.

23
gcc/expr.c
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@ -5827,20 +5827,21 @@ highest_pow2_factor (exp)
switch (TREE_CODE (exp))
{
case INTEGER_CST:
/* If the integer is expressable in a HOST_WIDE_INT, we can find the
lowest bit that's a one. If the result is zero, return
BIGGEST_ALIGNMENT. We need to handle this case since we can find it
in a COND_EXPR, a MIN_EXPR, or a MAX_EXPR. If the constant overlows,
we have an erroneous program, so return BIGGEST_ALIGNMENT to avoid any
/* We can find the lowest bit that's a one. If the low
HOST_BITS_PER_WIDE_INT bits are zero, return BIGGEST_ALIGNMENT.
We need to handle this case since we can find it in a COND_EXPR,
a MIN_EXPR, or a MAX_EXPR. If the constant overlows, we have an
erroneous program, so return BIGGEST_ALIGNMENT to avoid any
later ICE. */
if (TREE_CONSTANT_OVERFLOW (exp)
|| integer_zerop (exp))
if (TREE_CONSTANT_OVERFLOW (exp))
return BIGGEST_ALIGNMENT;
else if (host_integerp (exp, 0))
else
{
c0 = tree_low_cst (exp, 0);
c0 = c0 < 0 ? - c0 : c0;
return c0 & -c0;
/* Note: tree_low_cst is intentionally not used here,
we don't care about the upper bits. */
c0 = TREE_INT_CST_LOW (exp);
c0 &= -c0;
return c0 ? c0 : BIGGEST_ALIGNMENT;
}
break;