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Only do switch bit test clustering when multiple labels point to same bb

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The bit cluster code generation strategy is only beneficial when
multiple case labels point to the same code. Do a quick check if
that is the case before trying to cluster.

This fixes the switch part of PR117091 where all case labels are unique
however it doesn't address the performance problems for non unique
cases.

gcc/ChangeLog:

	PR middle-end/117091
	* gimple-if-to-switch.cc (if_chain::is_beneficial): Update
	find_bit_test call.
	* tree-switch-conversion.cc (bit_test_cluster::find_bit_tests):
	Get max_c argument and bail out early if all case labels are
	unique.
	(switch_decision_tree::compute_cases_per_edge): Record number of
	targets per label and return.
	(switch_decision_tree::analyze_switch_statement): ... pass to
	find_bit_tests.
	* tree-switch-conversion.h: Update prototypes.
This commit is contained in:
Andi Kleen 2024-10-16 14:07:18 -07:00
parent 06bc3a734e
commit a4e2b13888
3 changed files with 20 additions and 10 deletions
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2
gcc/gimple-if-to-switch.cc
View File

@ -255,7 +255,7 @@ if_chain::is_beneficial ()
else
output.release ();
output = bit_test_cluster::find_bit_tests (filtered_clusters);
output = bit_test_cluster::find_bit_tests (filtered_clusters, 2);
r = output.length () < filtered_clusters.length ();
if (r)
dump_clusters (&output, "BT can be built");

23
gcc/tree-switch-conversion.cc
View File

@ -1773,12 +1773,13 @@ jump_table_cluster::is_beneficial (const vec<cluster *> &,
}
/* Find bit tests of given CLUSTERS, where all members of the vector
are of type simple_cluster. New clusters are returned. */
are of type simple_cluster. MAX_C is the approx max number of cases per
label. New clusters are returned. */
vec<cluster *>
bit_test_cluster::find_bit_tests (vec<cluster *> &clusters)
bit_test_cluster::find_bit_tests (vec<cluster *> &clusters, int max_c)
{
if (!is_enabled ())
if (!is_enabled () || max_c == 1)
return clusters.copy ();
unsigned l = clusters.length ();
@ -2207,18 +2208,26 @@ bit_test_cluster::hoist_edge_and_branch_if_true (gimple_stmt_iterator *gsip,
}
/* Compute the number of case labels that correspond to each outgoing edge of
switch statement. Record this information in the aux field of the edge. */
switch statement. Record this information in the aux field of the edge.
Return the approx max number of cases per edge. */
void
int
switch_decision_tree::compute_cases_per_edge ()
{
int max_c = 0;
reset_out_edges_aux (m_switch);
int ncases = gimple_switch_num_labels (m_switch);
for (int i = ncases - 1; i >= 1; --i)
{
edge case_edge = gimple_switch_edge (cfun, m_switch, i);
case_edge->aux = (void *) ((intptr_t) (case_edge->aux) + 1);
/* For a range case add one extra. That's enough for the bit
cluster heuristic. */
if ((intptr_t)case_edge->aux > max_c)
max_c = (intptr_t)case_edge->aux +
!!CASE_HIGH (gimple_switch_label (m_switch, i));
}
return max_c;
}
/* Analyze switch statement and return true when the statement is expanded
@ -2236,7 +2245,7 @@ switch_decision_tree::analyze_switch_statement ()
m_case_bbs.reserve (l);
m_case_bbs.quick_push (default_bb);
compute_cases_per_edge ();
int max_c = compute_cases_per_edge ();
for (unsigned i = 1; i < l; i++)
{
@ -2257,7 +2266,7 @@ switch_decision_tree::analyze_switch_statement ()
reset_out_edges_aux (m_switch);
/* Find bit-test clusters. */
vec<cluster *> output = bit_test_cluster::find_bit_tests (clusters);
vec<cluster *> output = bit_test_cluster::find_bit_tests (clusters, max_c);
/* Find jump table clusters. */
vec<cluster *> output2;

5
gcc/tree-switch-conversion.h
View File

@ -399,7 +399,7 @@ public:
/* Find bit tests of given CLUSTERS, where all members of the vector
are of type simple_cluster. New clusters are returned. */
static vec<cluster *> find_bit_tests (vec<cluster *> &clusters);
static vec<cluster *> find_bit_tests (vec<cluster *> &clusters, int max_c);
/* Return true when RANGE of case values with UNIQ labels
can build a bit test. */
@ -576,8 +576,9 @@ public:
bool try_switch_expansion (vec<cluster *> &clusters);
/* Compute the number of case labels that correspond to each outgoing edge of
switch statement. Record this information in the aux field of the edge.
Returns approx max number of cases per edge.
*/
void compute_cases_per_edge ();
int compute_cases_per_edge ();
/* Before switch transformation, record all SSA_NAMEs defined in switch BB
and used in a label basic block. */