https://gcc.gnu.org/g:1a13684dfc7286139064f7d7341462c9995cbd1c
commit r16-303-g1a13684dfc7286139064f7d7341462c9995cbd1c
Author: Richard Biener <rguent...@suse.de>
Date: Wed Apr 30 11:52:17 2025 +0200
tree-optimization/120003 - missed jump threading
The following allows the entry and exit block of a jump thread path
to be equal, which can easily happen when there isn't a forwarder
on the interesting edge for an FSM thread conditional. We just
don't want to enlarge the path from such a block.
PR tree-optimization/120003
* tree-ssa-threadbackward.cc (back_threader::find_paths_to_names):
Allow block re-use but do not enlarge the path beyond such a
re-use.
* gcc.dg/tree-ssa/ssa-thread-23.c: New testcase.
* gcc.dg/tree-ssa/ssa-dom-thread-7.c: Adjust.
Diff:
---
gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-7.c | 4 ++--
gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-23.c | 19 +++++++++++++++++++
gcc/tree-ssa-threadbackward.cc | 8 +++-----
3 files changed, 24 insertions(+), 7 deletions(-)
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-7.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-7.c
index d84aceebc5d0..8be9878e0cfb 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-7.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-7.c
@@ -11,8 +11,8 @@
to change decisions in switch expansion which in turn can expose new
jump threading opportunities. Skip the later tests on aarch64. */
/* { dg-final { scan-tree-dump-not "Jumps threaded" "dom3" { target { !
aarch64*-*-* } } } } */
-/* { dg-final { scan-tree-dump "Jumps threaded: 9" "thread2" { target { !
aarch64*-*-* } } } } */
-/* { dg-final { scan-tree-dump "Jumps threaded: 17" "thread2" { target {
aarch64*-*-* } } } } */
+/* { dg-final { scan-tree-dump "Jumps threaded: 10" "thread2" { target { !
aarch64*-*-* } } } } */
+/* { dg-final { scan-tree-dump "Jumps threaded: 14" "thread2" { target {
aarch64*-*-* } } } } */
enum STATE {
S0=0,
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-23.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-23.c
new file mode 100644
index 000000000000..930360a33b57
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-thread-23.c
@@ -0,0 +1,19 @@
+/* PR120003 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-cddce3-details" } */
+
+extern _Bool g(int);
+
+_Bool f()
+{
+ _Bool retval = 0;
+ for(int i=0; i<1000000; ++i)
+ retval = retval || g(i);
+ return retval;
+}
+
+/* Jump threading after loop optimization should get the counting loop
+ separated from the loop until retval is true and CD-DCE elide it.
+ It's difficult to check for the fact that a true retval terminates
+ the loop so check CD-DCE eliminates one loop instead. */
+/* { dg-final { scan-tree-dump "fix_loop_structure: removing loop" "cddce3" }
} */
diff --git a/gcc/tree-ssa-threadbackward.cc b/gcc/tree-ssa-threadbackward.cc
index d0b74b2531df..3adb83e97126 100644
--- a/gcc/tree-ssa-threadbackward.cc
+++ b/gcc/tree-ssa-threadbackward.cc
@@ -349,9 +349,6 @@ back_threader::find_paths_to_names (basic_block bb, bitmap
interesting,
unsigned overall_paths,
back_threader_profitability &profit)
{
- if (m_visited_bbs.add (bb))
- return;
-
m_path.safe_push (bb);
// Try to resolve the path without looking back. Avoid resolving paths
@@ -377,7 +374,8 @@ back_threader::find_paths_to_names (basic_block bb, bitmap
interesting,
// Continue looking for ways to extend the path but limit the
// search space along a branch
else if ((overall_paths = overall_paths * EDGE_COUNT (bb->preds))
- <= (unsigned)param_max_jump_thread_paths)
+ <= (unsigned)param_max_jump_thread_paths
+ && !m_visited_bbs.add (bb))
{
// For further greedy searching we want to remove interesting
// names defined in BB but add ones on the PHI edges for the
@@ -489,6 +487,7 @@ back_threader::find_paths_to_names (basic_block bb, bitmap
interesting,
backtracking we have to restore it. */
for (int j : new_imports)
bitmap_clear_bit (m_imports, j);
+ m_visited_bbs.remove (bb);
}
else if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, " FAIL: Search space limit %d reached.\n",
@@ -496,7 +495,6 @@ back_threader::find_paths_to_names (basic_block bb, bitmap
interesting,
// Reset things to their original state.
m_path.pop ();
- m_visited_bbs.remove (bb);
}
// Search backwards from BB looking for paths where the final
