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8219922: Simplify and optimize IndexSetIterator::next using count_trailing_zeros

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Reviewed-by: kvn, neliasso
This commit is contained in:
Claes Redestad 2019-02-28 22:11:46 +01:00
parent ba84c4bc0c
commit 29d842b5a0
2 changed files with 6 additions and 90 deletions
src/hotspot/share/opto
indexSet.cppindexSet.hpp

66
src/hotspot/share/opto/indexSet.cpp

@ -50,72 +50,6 @@ julong IndexSet::_total_unused_blocks = 0;
int IndexSet::_serial_count = 1;
#endif
// What is the first set bit in a 5 bit integer?
const uint8_t IndexSetIterator::_first_bit[32] = {
0, 0, 1, 0,
2, 0, 1, 0,
3, 0, 1, 0,
2, 0, 1, 0,
4, 0, 1, 0,
2, 0, 1, 0,
3, 0, 1, 0,
2, 0, 1, 0
};
// What is the second set bit in a 5 bit integer?
const uint8_t IndexSetIterator::_second_bit[32] = {
5, 5, 5, 1,
5, 2, 2, 1,
5, 3, 3, 1,
3, 2, 2, 1,
5, 4, 4, 1,
4, 2, 2, 1,
4, 3, 3, 1,
3, 2, 2, 1
};
// I tried implementing the IndexSetIterator with a window_size of 8 and
// didn't seem to get a noticeable speedup. I am leaving in the tables
// in case we want to switch back.
/*const byte IndexSetIterator::_first_bit[256] = {
8, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
7, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
6, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
5, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0,
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
};
const byte IndexSetIterator::_second_bit[256] = {
8, 8, 8, 1, 8, 2, 2, 1, 8, 3, 3, 1, 3, 2, 2, 1,
8, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1,
8, 5, 5, 1, 5, 2, 2, 1, 5, 3, 3, 1, 3, 2, 2, 1,
5, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1,
8, 6, 6, 1, 6, 2, 2, 1, 6, 3, 3, 1, 3, 2, 2, 1,
6, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1,
6, 5, 5, 1, 5, 2, 2, 1, 5, 3, 3, 1, 3, 2, 2, 1,
5, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1,
8, 7, 7, 1, 7, 2, 2, 1, 7, 3, 3, 1, 3, 2, 2, 1,
7, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1,
7, 5, 5, 1, 5, 2, 2, 1, 5, 3, 3, 1, 3, 2, 2, 1,
5, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1,
7, 6, 6, 1, 6, 2, 2, 1, 6, 3, 3, 1, 3, 2, 2, 1,
6, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1,
6, 5, 5, 1, 5, 2, 2, 1, 5, 3, 3, 1, 3, 2, 2, 1,
5, 4, 4, 1, 4, 2, 2, 1, 4, 3, 3, 1, 3, 2, 2, 1
};*/
//---------------------------- IndexSet::populate_free_list() -----------------------------
// Populate the free BitBlock list with a batch of BitBlocks. The BitBlocks
// are 32 bit aligned.

30
src/hotspot/share/opto/indexSet.hpp

@ -29,6 +29,7 @@
#include "memory/resourceArea.hpp"
#include "opto/compile.hpp"
#include "opto/regmask.hpp"
#include "utilities/count_trailing_zeros.hpp"
// This file defines the IndexSet class, a set of sparse integer indices.
// This data structure is used by the compiler in its liveness analysis and
@ -396,19 +397,6 @@ class IndexSet : public ResourceObj {
class IndexSetIterator {
friend class IndexSet;
public:
// We walk over the bits in a word in chunks of size window_size.
enum { window_size = 5,
window_mask = right_n_bits(window_size),
table_size = (1 << window_size) };
// For an integer of length window_size, what is the first set bit?
static const uint8_t _first_bit[table_size];
// For an integer of length window_size, what is the second set bit?
static const uint8_t _second_bit[table_size];
private:
// The current word we are inspecting
uint32_t _current;
@ -440,7 +428,6 @@ class IndexSetIterator {
// element in the set.
uint advance_and_next();
public:
// If an iterator is built from a constant set then empty blocks
@ -452,16 +439,11 @@ class IndexSetIterator {
uint next() {
uint current = _current;
if (current != 0) {
uint value = _value;
while (mask_bits(current,window_mask) == 0) {
current >>= window_size;
value += window_size;
}
uint advance = _second_bit[mask_bits(current,window_mask)];
_current = current >> advance;
_value = value + advance;
return value + _first_bit[mask_bits(current,window_mask)];
uint advance = count_trailing_zeros(current);
assert((current >> advance) & 0x1 == 1, "sanity");
_current = (current >> advance) - 1;
_value += advance;
return _value;
} else {
return advance_and_next();
}