https://gcc.gnu.org/g:2cf89ae83225f932b226cd57ef2d083a59bcf8a3
commit r15-2789-g2cf89ae83225f932b226cd57ef2d083a59bcf8a3
Author: Richard Biener <rguent...@suse.de>
Date: Tue Aug 6 14:56:26 2024 +0200
tree-optimization/116166 - forward jump-threading going wild
Currently the forward threader isn't limited as to the search space
it explores and with it now using path-ranger for simplifying
conditions it runs into it became pretty slow for degenerate cases
like compiling insn-emit.cc for RISC-V esp. when compiling for
a host with LOGICAL_OP_NON_SHORT_CIRCUIT disabled.
The following makes the forward threader honor the search space
limit I introduced for the backward threader. This reduces
compile-time from minutes to seconds for the testcase in PR116166.
Note this wasn't necessary before we had ranger but with ranger
the work we do is quadatic in the length of the threading path
we build up (the same is true for the backwards threader).
PR tree-optimization/116166
* tree-ssa-threadedge.h (jump_threader::thread_around_empty_blocks):
Add limit parameter.
(jump_threader::thread_through_normal_block): Likewise.
* tree-ssa-threadedge.cc
(jump_threader::thread_around_empty_blocks):
Honor and decrement limit parameter.
(jump_threader::thread_through_normal_block): Likewise.
(jump_threader::thread_across_edge): Initialize limit from
param_max_jump_thread_paths and pass it down to workers.
Diff:
---
gcc/tree-ssa-threadedge.cc | 30 ++++++++++++++++++++++--------
gcc/tree-ssa-threadedge.h | 4 ++--
2 files changed, 24 insertions(+), 10 deletions(-)
diff --git a/gcc/tree-ssa-threadedge.cc b/gcc/tree-ssa-threadedge.cc
index 7f82639b8ecc..0aa2aa851430 100644
--- a/gcc/tree-ssa-threadedge.cc
+++ b/gcc/tree-ssa-threadedge.cc
@@ -786,13 +786,17 @@ propagate_threaded_block_debug_into (basic_block dest,
basic_block src)
bool
jump_threader::thread_around_empty_blocks (vec<jump_thread_edge *> *path,
edge taken_edge,
- bitmap visited)
+ bitmap visited, unsigned &limit)
{
basic_block bb = taken_edge->dest;
gimple_stmt_iterator gsi;
gimple *stmt;
tree cond;
+ if (limit == 0)
+ return false;
+ --limit;
+
/* The key property of these blocks is that they need not be duplicated
when threading. Thus they cannot have visible side effects such
as PHI nodes. */
@@ -830,7 +834,8 @@ jump_threader::thread_around_empty_blocks
(vec<jump_thread_edge *> *path,
m_registry->push_edge (path, taken_edge, EDGE_NO_COPY_SRC_BLOCK);
m_state->append_path (taken_edge->dest);
bitmap_set_bit (visited, taken_edge->dest->index);
- return thread_around_empty_blocks (path, taken_edge, visited);
+ return thread_around_empty_blocks (path, taken_edge, visited,
+ limit);
}
}
@@ -872,7 +877,7 @@ jump_threader::thread_around_empty_blocks
(vec<jump_thread_edge *> *path,
m_registry->push_edge (path, taken_edge, EDGE_NO_COPY_SRC_BLOCK);
m_state->append_path (taken_edge->dest);
- thread_around_empty_blocks (path, taken_edge, visited);
+ thread_around_empty_blocks (path, taken_edge, visited, limit);
return true;
}
@@ -899,8 +904,13 @@ jump_threader::thread_around_empty_blocks
(vec<jump_thread_edge *> *path,
int
jump_threader::thread_through_normal_block (vec<jump_thread_edge *> *path,
- edge e, bitmap visited)
+ edge e, bitmap visited,
+ unsigned &limit)
{
+ if (limit == 0)
+ return 0;
+ limit--;
+
m_state->register_equivs_edge (e);
/* PHIs create temporary equivalences.
@@ -989,7 +999,7 @@ jump_threader::thread_through_normal_block
(vec<jump_thread_edge *> *path,
visited. This may be overly conservative. */
bitmap_set_bit (visited, dest->index);
bitmap_set_bit (visited, e->dest->index);
- thread_around_empty_blocks (path, taken_edge, visited);
+ thread_around_empty_blocks (path, taken_edge, visited, limit);
return 1;
}
}
@@ -1075,9 +1085,12 @@ jump_threader::thread_across_edge (edge e)
bitmap_set_bit (visited, e->src->index);
bitmap_set_bit (visited, e->dest->index);
+ /* Limit search space. */
+ unsigned limit = param_max_jump_thread_paths;
+
int threaded = 0;
if ((e->flags & EDGE_DFS_BACK) == 0)
- threaded = thread_through_normal_block (path, e, visited);
+ threaded = thread_through_normal_block (path, e, visited, limit);
if (threaded > 0)
{
@@ -1148,11 +1161,12 @@ jump_threader::thread_across_edge (edge e)
m_registry->push_edge (path, e, EDGE_START_JUMP_THREAD);
m_registry->push_edge (path, taken_edge, EDGE_COPY_SRC_JOINER_BLOCK);
- found = thread_around_empty_blocks (path, taken_edge, visited);
+ found = thread_around_empty_blocks (path, taken_edge, visited, limit);
if (!found)
found = thread_through_normal_block (path,
- path->last ()->e, visited) > 0;
+ path->last ()->e, visited,
+ limit) > 0;
/* If we were able to thread through a successor of E->dest, then
record the jump threading opportunity. */
diff --git a/gcc/tree-ssa-threadedge.h b/gcc/tree-ssa-threadedge.h
index 9f6cbfe93307..245b3506a550 100644
--- a/gcc/tree-ssa-threadedge.h
+++ b/gcc/tree-ssa-threadedge.h
@@ -101,9 +101,9 @@ private:
unsigned limit);
bool thread_around_empty_blocks (vec<class jump_thread_edge *> *path,
- edge, bitmap visited);
+ edge, bitmap visited, unsigned &limit);
int thread_through_normal_block (vec<jump_thread_edge *> *path,
- edge, bitmap visited);
+ edge, bitmap visited, unsigned &limit);
void thread_across_edge (edge);
bool record_temporary_equivalences_from_phis (edge);
gimple *record_temporary_equivalences_from_stmts_at_dest (edge);
