Hi!
This patch adds a small optimization to emit_case_bit_tests,
instead of emitting (for high, low, mask all constants)
(x - low) <= (high - low) && ((1 << (x - low)) & mask)
if high is smaller than BITS_PER_WORD and low > 0 we can emit
x <= high && ((1 << x) & (mask << low))
and avoid subtraction. Do this only if mask << low isn't more costly than
mask.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2014-10-10 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/63464
* tree-switch-conversion.c (struct case_bit_test): Remove
hi and lo fields, add wide_int mask field.
(emit_case_bit_tests): Add MAXVAL argument, rewrite uses of
hi/lo fields into wide_int mask operations, optimize by pretending
minval to be 0 if maxval is small enough.
(process_switch): Adjust caller.
--- gcc/tree-switch-conversion.c.jj 2014-08-01 09:24:12.000000000 +0200
+++ gcc/tree-switch-conversion.c 2014-10-07 12:36:29.438181857 +0200
@@ -246,8 +246,7 @@ This transformation was contributed by R
struct case_bit_test
{
- HOST_WIDE_INT hi;
- HOST_WIDE_INT lo;
+ wide_int mask;
edge target_edge;
tree label;
int bits;
@@ -294,13 +293,14 @@ case_bit_test_cmp (const void *p1, const
are not guaranteed to be of the same type as INDEX_EXPR
(the gimplifier doesn't change the type of case label values,
and MINVAL and RANGE are derived from those values).
+ MAXVAL is MINVAL + RANGE.
There *MUST* be MAX_CASE_BIT_TESTS or less unique case
node targets. */
static void
emit_case_bit_tests (gimple swtch, tree index_expr,
- tree minval, tree range)
+ tree minval, tree range, tree maxval)
{
struct case_bit_test test[MAX_CASE_BIT_TESTS];
unsigned int i, j, k;
@@ -324,6 +324,8 @@ emit_case_bit_tests (gimple swtch, tree
tree word_type_node = lang_hooks.types.type_for_mode (word_mode, 1);
tree word_mode_zero = fold_convert (word_type_node, integer_zero_node);
tree word_mode_one = fold_convert (word_type_node, integer_one_node);
+ int prec = TYPE_PRECISION (word_type_node);
+ wide_int wone = wi::one (prec);
memset (&test, 0, sizeof (test));
@@ -348,8 +350,7 @@ emit_case_bit_tests (gimple swtch, tree
if (k == count)
{
gcc_checking_assert (count < MAX_CASE_BIT_TESTS);
- test[k].hi = 0;
- test[k].lo = 0;
+ test[k].mask = wi::zero (prec);
test[k].target_edge = e;
test[k].label = label;
test[k].bits = 1;
@@ -367,14 +368,39 @@ emit_case_bit_tests (gimple swtch, tree
CASE_HIGH (cs), minval));
for (j = lo; j <= hi; j++)
- if (j >= HOST_BITS_PER_WIDE_INT)
- test[k].hi |= (HOST_WIDE_INT) 1 << (j - HOST_BITS_PER_INT);
- else
- test[k].lo |= (HOST_WIDE_INT) 1 << j;
+ test[k].mask |= wi::lshift (wone, j);
}
qsort (test, count, sizeof (*test), case_bit_test_cmp);
+ /* If all values are in the 0 .. BITS_PER_WORD-1 range, we can get rid of
+ the minval subtractions, but it might make the mask constants more
+ expensive. So, compare the costs. */
+ if (compare_tree_int (minval, 0) > 0
+ && compare_tree_int (maxval, GET_MODE_BITSIZE (word_mode)) < 0)
+ {
+ int cost_diff;
+ HOST_WIDE_INT m = tree_to_uhwi (minval);
+ rtx reg = gen_raw_REG (word_mode, 10000);
+ bool speed_p = optimize_bb_for_speed_p (gimple_bb (swtch));
+ cost_diff = set_rtx_cost (gen_rtx_PLUS (word_mode, reg,
+ GEN_INT (-m)), speed_p);
+ for (i = 0; i < count; i++)
+ {
+ rtx r = immed_wide_int_const (test[i].mask, word_mode);
+ cost_diff += set_src_cost (gen_rtx_AND (word_mode, reg, r), speed_p);
+ r = immed_wide_int_const (wi::lshift (test[i].mask, m), word_mode);
+ cost_diff -= set_src_cost (gen_rtx_AND (word_mode, reg, r), speed_p);
+ }
+ if (cost_diff > 0)
+ {
+ for (i = 0; i < count; i++)
+ test[i].mask = wi::lshift (test[i].mask, m);
+ minval = build_zero_cst (TREE_TYPE (minval));
+ range = maxval;
+ }
+ }
+
/* We generate two jumps to the default case label.
Split the default edge, so that we don't have to do any PHI node
updating. */
@@ -446,13 +472,7 @@ emit_case_bit_tests (gimple swtch, tree
if (const & csui) goto target */
for (k = 0; k < count; k++)
{
- HOST_WIDE_INT a[2];
-
- a[0] = test[k].lo;
- a[1] = test[k].hi;
- tmp = wide_int_to_tree (word_type_node,
- wide_int::from_array (a, 2,
- TYPE_PRECISION
(word_type_node)));
+ tmp = wide_int_to_tree (word_type_node, test[k].mask);
tmp = fold_build2 (BIT_AND_EXPR, word_type_node, csui, tmp);
tmp = force_gimple_operand_gsi (&gsi, tmp,
/*simple=*/true, NULL_TREE,
@@ -1369,8 +1389,8 @@ process_switch (gimple swtch)
{
if (dump_file)
fputs (" expanding as bit test is preferable\n", dump_file);
- emit_case_bit_tests (swtch, info.index_expr,
- info.range_min, info.range_size);
+ emit_case_bit_tests (swtch, info.index_expr, info.range_min,
+ info.range_size, info.range_max);
loops_state_set (LOOPS_NEED_FIXUP);
return NULL;
}
Jakub
