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re PR rtl-optimization/26026 (power of 2 mod missing optimisation)

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PR rtl-optimization/26026
	* fold-const.c (fold_binary): Optimize div and mod where the divisor
	is a known power of two shifted left a variable amount.

From-SVN: r113060
This commit is contained in:
Alan Modra 2006-04-18 23:45:47 +00:00 • committed by Alan Modra
parent 76f7a74ff6
commit 0f35201e17
2 changed files with 39 additions and 21 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2006-04-19 Alan Modra <amodra@bigpond.net.au>
PR rtl-optimization/26026
* fold-const.c (fold_binary): Optimize div and mod where the divisor
is a known power of two shifted left a variable amount.
2006-04-18 Geoffrey Keating <geoffk@apple.com>
* dwarf2out.c (prune_unused_types_update_strings): Don't add strings

54
gcc/fold-const.c
View file

@ -9600,8 +9600,27 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
return NULL_TREE;
case TRUNC_DIV_EXPR:
case ROUND_DIV_EXPR:
case FLOOR_DIV_EXPR:
/* Simplify A / (B << N) where A and B are positive and B is
a power of 2, to A >> (N + log2(B)). */
if (TREE_CODE (arg1) == LSHIFT_EXPR
&& (TYPE_UNSIGNED (type) || tree_expr_nonnegative_p (arg0)))
{
tree sval = TREE_OPERAND (arg1, 0);
if (integer_pow2p (sval) && tree_int_cst_sgn (sval) > 0)
{
tree sh_cnt = TREE_OPERAND (arg1, 1);
unsigned long pow2 = exact_log2 (TREE_INT_CST_LOW (sval));
sh_cnt = fold_build2 (PLUS_EXPR, TREE_TYPE (sh_cnt),
sh_cnt, build_int_cst (NULL_TREE, pow2));
return fold_build2 (RSHIFT_EXPR, type,
fold_convert (type, arg0), sh_cnt);
}
}
/* Fall thru */
case ROUND_DIV_EXPR:
case CEIL_DIV_EXPR:
case EXACT_DIV_EXPR:
if (integer_onep (arg1))
@ -9671,31 +9690,24 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
return omit_one_operand (type, integer_zero_node, arg0);
/* 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. */
i.e. "X % C" into "X & (C - 1)", 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)
&& (TYPE_UNSIGNED (type) || tree_expr_nonnegative_p (arg0)))
{
unsigned HOST_WIDE_INT high, low;
tree mask;
int l;
tree c = arg1;
/* Also optimize A % (C << N) where C is a power of 2,
to A & ((C << N) - 1). */
if (TREE_CODE (arg1) == LSHIFT_EXPR)
c = TREE_OPERAND (arg1, 0);
l = tree_log2 (arg1);
if (l >= HOST_BITS_PER_WIDE_INT)
if (integer_pow2p (c) && tree_int_cst_sgn (c) > 0)
{
high = ((unsigned HOST_WIDE_INT) 1
<< (l - HOST_BITS_PER_WIDE_INT)) - 1;
low = -1;
tree mask = fold_build2 (MINUS_EXPR, TREE_TYPE (arg1),
arg1, integer_one_node);
return fold_build2 (BIT_AND_EXPR, type,
fold_convert (type, arg0),
fold_convert (type, mask));
}
else
{
high = 0;
low = ((unsigned HOST_WIDE_INT) 1 << l) - 1;
}
mask = build_int_cst_wide (type, low, high);
return fold_build2 (BIT_AND_EXPR, type,
fold_convert (type, arg0), mask);
}
/* X % -C is the same as X % C. */