Hello.
All right, I come up with a rapid speed up that can allow us to remove
the introduced parameter. It contains 2 parts:
- BIT TEST: we allow at maximum a range that is smaller GET_MODE_BITSIZE
- JT: we spent quite some time in density calculation, we can guess it first
and it leads to a fast bail out.
Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
Ready to be installed?
Thanks,
Martin
>From dc4c1d129a50c7f51d28235506479f29d51dae07 Mon Sep 17 00:00:00 2001
From: Martin Liska <mli...@suse.cz>
Date: Thu, 24 Sep 2020 13:34:13 +0200
Subject: [PATCH 2/2] switch conversion: make a rapid speed up
gcc/ChangeLog:
PR tree-optimization/96979
* tree-switch-conversion.c (jump_table_cluster::can_be_handled):
Make a fast bail out.
(bit_test_cluster::can_be_handled): Likewise here.
* tree-switch-conversion.h (get_range): Use wi::to_wide instead
of a folding.
gcc/testsuite/ChangeLog:
PR tree-optimization/96979
* g++.dg/tree-ssa/pr96979.C: New test.
---
gcc/testsuite/g++.dg/tree-ssa/pr96979.C | 48 +++++++++++++++++++++++++
gcc/tree-switch-conversion.c | 32 ++++++++++++-----
gcc/tree-switch-conversion.h | 7 ++--
3 files changed, 74 insertions(+), 13 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr96979.C
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr96979.C b/gcc/testsuite/g++.dg/tree-ssa/pr96979.C
new file mode 100644
index 00000000000..ec0f57a8548
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr96979.C
@@ -0,0 +1,48 @@
+/* PR tree-optimization/96979 */
+/* { dg-do compile } */
+/* { dg-options "-std=c++17 -O2" } */
+
+using u64 = unsigned long long;
+
+constexpr inline u64
+foo (const char *str) noexcept
+{
+ u64 value = 0xcbf29ce484222325ULL;
+ for (u64 i = 0; str[i]; i++)
+ value = (value ^ u64(str[i])) * 0x100000001b3ULL;
+ return value;
+}
+
+struct V
+{
+ enum W
+ {
+#define A(n) n,
+#define B(n) A(n##0) A(n##1) A(n##2) A(n##3) A(n##4) A(n##5) A(n##6) A(n##7) A(n##8) A(n##9)
+#define C(n) B(n##0) B(n##1) B(n##2) B(n##3) B(n##4) B(n##5) B(n##6) B(n##7) B(n##8) B(n##9)
+#define D(n) C(n##0) C(n##1) C(n##2) C(n##3) C(n##4) C(n##5) C(n##6) C(n##7) C(n##8) C(n##9)
+#define E D(foo1) D(foo2) D(foo3)
+ E
+ last
+ };
+
+ constexpr static W
+ bar (const u64 h) noexcept
+ {
+ switch (h)
+ {
+#undef A
+#define F(n) #n
+#define A(n) case foo (F(n)): return n;
+ E
+ }
+ return last;
+ }
+};
+
+int
+baz (const char *s)
+{
+ const u64 h = foo (s);
+ return V::bar (h);
+}
diff --git a/gcc/tree-switch-conversion.c b/gcc/tree-switch-conversion.c
index 186411ff3c4..3212e964b84 100644
--- a/gcc/tree-switch-conversion.c
+++ b/gcc/tree-switch-conversion.c
@@ -1268,6 +1268,15 @@ jump_table_cluster::can_be_handled (const vec<cluster *> &clusters,
if (range == 0)
return false;
+ unsigned HOST_WIDE_INT lhs = 100 * range;
+ if (lhs < range)
+ return false;
+
+ /* First make quick guess as each cluster
+ can add at maximum 2 to the comparison_count. */
+ if (lhs > 2 * max_ratio * (end - start + 1))
+ return false;
+
unsigned HOST_WIDE_INT comparison_count = 0;
for (unsigned i = start; i <= end; i++)
{
@@ -1275,10 +1284,6 @@ jump_table_cluster::can_be_handled (const vec<cluster *> &clusters,
comparison_count += sc->m_range_p ? 2 : 1;
}
- unsigned HOST_WIDE_INT lhs = 100 * range;
- if (lhs < range)
- return false;
-
return lhs <= max_ratio * comparison_count;
}
@@ -1364,12 +1369,12 @@ bit_test_cluster::can_be_handled (unsigned HOST_WIDE_INT range,
{
/* Check overflow. */
if (range == 0)
- return 0;
+ return false;
if (range >= GET_MODE_BITSIZE (word_mode))
return false;
- return uniq <= 3;
+ return uniq <= m_max_case_bit_tests;
}
/* Return true when cluster starting at START and ending at END (inclusive)
@@ -1379,6 +1384,7 @@ bool
bit_test_cluster::can_be_handled (const vec<cluster *> &clusters,
unsigned start, unsigned end)
{
+ auto_vec<int> dest_bbs;
/* For algorithm correctness, bit test for a single case must return
true. We bail out in is_beneficial if it's called just for
a single case. */
@@ -1387,15 +1393,23 @@ bit_test_cluster::can_be_handled (const vec<cluster *> &clusters,
unsigned HOST_WIDE_INT range = get_range (clusters[start]->get_low (),
clusters[end]->get_high ());
- auto_bitmap dest_bbs;
+
+ /* Make a guess first. */
+ if (!can_be_handled (range, m_max_case_bit_tests))
+ return false;
for (unsigned i = start; i <= end; i++)
{
simple_cluster *sc = static_cast<simple_cluster *> (clusters[i]);
- bitmap_set_bit (dest_bbs, sc->m_case_bb->index);
+ if (!dest_bbs.contains (sc->m_case_bb->index))
+ {
+ dest_bbs.safe_push (sc->m_case_bb->index);
+ if (dest_bbs.length () > m_max_case_bit_tests)
+ return false;
+ }
}
- return can_be_handled (range, bitmap_count_bits (dest_bbs));
+ return true;
}
/* Return true when COUNT of cases of UNIQ labels is beneficial for bit test
diff --git a/gcc/tree-switch-conversion.h b/gcc/tree-switch-conversion.h
index 9ebcf109319..dbfd9eecba2 100644
--- a/gcc/tree-switch-conversion.h
+++ b/gcc/tree-switch-conversion.h
@@ -84,11 +84,10 @@ public:
then return 0. */
static unsigned HOST_WIDE_INT get_range (tree low, tree high)
{
- tree r = fold_build2 (MINUS_EXPR, TREE_TYPE (low), high, low);
- if (!tree_fits_uhwi_p (r))
+ wide_int w = wi::to_wide (high) - wi::to_wide (low);
+ if (wi::neg_p (w, TYPE_SIGN (TREE_TYPE (low))) || !wi::fits_uhwi_p (w))
return 0;
-
- return tree_to_uhwi (r) + 1;
+ return w.to_uhwi () + 1;
}
/* Case label. */
--
2.28.0
>From e1956c0019d8df4a022ea17bc76f9e62fac182c7 Mon Sep 17 00:00:00 2001
From: Martin Liska <mli...@suse.cz>
Date: Thu, 24 Sep 2020 13:34:58 +0200
Subject: [PATCH 1/2] Revert "switch lowering: limit number of cluster attemps"
This reverts commit c6df6039e9180c580945266302ec14047d358364.
---
gcc/doc/invoke.texi | 4 --
gcc/params.opt | 4 --
gcc/testsuite/g++.dg/tree-ssa/pr96979.C | 50 -------------------------
gcc/tree-switch-conversion.c | 17 ---------
4 files changed, 75 deletions(-)
delete mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr96979.C
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 75203ba2420..08f1102030c 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -13471,10 +13471,6 @@ The smallest number of different values for which it is best to use a
jump-table instead of a tree of conditional branches. If the value is
0, use the default for the machine.
-@item max-switch-clustering-attempts
-The maximum number of clustering attempts used
-in bit-test and jump-table switch expansion.
-
@item jump-table-max-growth-ratio-for-size
The maximum code size growth ratio when expanding
into a jump table (in percent). The parameter is used when
diff --git a/gcc/params.opt b/gcc/params.opt
index 5f2e11d6c57..dcf5e020f01 100644
--- a/gcc/params.opt
+++ b/gcc/params.opt
@@ -82,10 +82,6 @@ The maximum length of a constant string for a builtin string cmp call eligible f
Common Joined UInteger Var(param_case_values_threshold) Param Optimization
The smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches, if 0, use the default for the machine.
--param=max-switch-clustering-attempts=
-Common Joined UInteger Var(param_max_switch_clustering_attempts) Param Optimization Init(10000)
-The maximum number of clustering attempts used in bit-test and jump-table switch expansion.
-
-param=comdat-sharing-probability=
Common Joined UInteger Var(param_comdat_sharing_probability) Init(20) Param Optimization
Probability that COMDAT function will be shared with different compilation unit.
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr96979.C b/gcc/testsuite/g++.dg/tree-ssa/pr96979.C
deleted file mode 100644
index 85c703a140d..00000000000
--- a/gcc/testsuite/g++.dg/tree-ssa/pr96979.C
+++ /dev/null
@@ -1,50 +0,0 @@
-/* PR tree-optimization/96979 */
-/* { dg-do compile } */
-/* { dg-options "-std=c++17 -O2 -fdump-tree-switchlower1" } */
-
-using u64 = unsigned long long;
-
-constexpr inline u64
-foo (const char *str) noexcept
-{
- u64 value = 0xcbf29ce484222325ULL;
- for (u64 i = 0; str[i]; i++)
- value = (value ^ u64(str[i])) * 0x100000001b3ULL;
- return value;
-}
-
-struct V
-{
- enum W
- {
-#define A(n) n,
-#define B(n) A(n##0) A(n##1) A(n##2) A(n##3) A(n##4) A(n##5) A(n##6) A(n##7) A(n##8) A(n##9)
-#define C(n) B(n##0) B(n##1) B(n##2) B(n##3) B(n##4) B(n##5) B(n##6) B(n##7) B(n##8) B(n##9)
-#define D(n) C(n##0) C(n##1) C(n##2) C(n##3) C(n##4) C(n##5) C(n##6) C(n##7) C(n##8) C(n##9)
-#define E D(foo1) D(foo2) D(foo3)
- E
- last
- };
-
- constexpr static W
- bar (const u64 h) noexcept
- {
- switch (h)
- {
-#undef A
-#define F(n) #n
-#define A(n) case foo (F(n)): return n;
- E
- }
- return last;
- }
-};
-
-int
-baz (const char *s)
-{
- const u64 h = foo (s);
- return V::bar (h);
-}
-
-/* { dg-final { scan-tree-dump-times ";; Bail out: --param=max-switch-clustering-attempts reached" 2 "switchlower1" } } */
diff --git a/gcc/tree-switch-conversion.c b/gcc/tree-switch-conversion.c
index e6a2c7a6a84..186411ff3c4 100644
--- a/gcc/tree-switch-conversion.c
+++ b/gcc/tree-switch-conversion.c
@@ -1183,7 +1183,6 @@ jump_table_cluster::find_jump_tables (vec<cluster *> &clusters)
min.quick_push (min_cluster_item (0, 0, 0));
- HOST_WIDE_INT attempts = 0;
for (unsigned i = 1; i <= l; i++)
{
/* Set minimal # of clusters with i-th item to infinite. */
@@ -1195,14 +1194,6 @@ jump_table_cluster::find_jump_tables (vec<cluster *> &clusters)
if (i - j < case_values_threshold ())
s += i - j;
- if (attempts++ == param_max_switch_clustering_attempts)
- {
- if (dump_file)
- fprintf (dump_file, ";; Bail out: "
- "--param=max-switch-clustering-attempts reached\n");
- return clusters.copy ();
- }
-
/* Prefer clusters with smaller number of numbers covered. */
if ((min[j].m_count + 1 < min[i].m_count
|| (min[j].m_count + 1 == min[i].m_count
@@ -1317,7 +1308,6 @@ bit_test_cluster::find_bit_tests (vec<cluster *> &clusters)
min.quick_push (min_cluster_item (0, 0, 0));
- HOST_WIDE_INT attempts = 0;
for (unsigned i = 1; i <= l; i++)
{
/* Set minimal # of clusters with i-th item to infinite. */
@@ -1325,13 +1315,6 @@ bit_test_cluster::find_bit_tests (vec<cluster *> &clusters)
for (unsigned j = 0; j < i; j++)
{
- if (attempts++ == param_max_switch_clustering_attempts)
- {
- if (dump_file)
- fprintf (dump_file, ";; Bail out: "
- "--param=max-switch-clustering-attempts reached\n");
- return clusters.copy ();
- }
if (min[j].m_count + 1 < min[i].m_count
&& can_be_handled (clusters, j, i - 1))
min[i] = min_cluster_item (min[j].m_count + 1, j, INT_MAX);
--
2.28.0
