As discussed in PR126103, the first step to removing DOM is untangling
its threader from the rest of DOM. I've started auditing what we're
missing in PRE + backwards threader, and need a way to disable DOM's
threading for the barrage of PRs I'm about to file.
We already have a way to disable all jump threads, but no way to
disable just DOM's. This patch does jhust this with
--param=dom-jump-threading=[01]. It's in line with what we
temporarily did for ranger-threading and ranger VRP.
The --param disables jump threading in DOM, but everything else DOM
does is unaffected.
OK for trunk?
Tested on ppc64le Linux.
PR tree-optimization/126103
gcc/ChangeLog:
* doc/params.texi (dom-jump-threading): Document.
* params.opt (-param=dom-jump-threading=): New.
* tree-ssa-dom.cc (dom_opt_dom_walker::after_dom_children): Honor
param_dom_jump_threading.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/dom-jump-threading-1.c: New test.
* gcc.dg/tree-ssa/dom-jump-threading-2.c: New test.
---
gcc/doc/params.texi | 6 +++++
gcc/params.opt | 4 ++++
.../gcc.dg/tree-ssa/dom-jump-threading-1.c | 24 +++++++++++++++++++
.../gcc.dg/tree-ssa/dom-jump-threading-2.c | 22 +++++++++++++++++
gcc/tree-ssa-dom.cc | 3 ++-
5 files changed, 58 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/dom-jump-threading-1.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/dom-jump-threading-2.c
diff --git a/gcc/doc/params.texi b/gcc/doc/params.texi
index 26b34a59aa9..e69be2d2923 100644
--- a/gcc/doc/params.texi
+++ b/gcc/doc/params.texi
@@ -894,6 +894,12 @@ optimizing.
Maximum number of dominators BBs to walk when simplifying loop bounds
and conditions.
+@paindex dom-jump-threading
+@item dom-jump-threading
+Enable jump threading in the dominator optimizer pass. Disabling it
+is useful to isolate the jump threads found by the backward threader,
+which runs regardless.
+
@paindex max-jump-thread-duplication-stmts
@item max-jump-thread-duplication-stmts
Maximum number of statements allowed in a block that needs to be
diff --git a/gcc/params.opt b/gcc/params.opt
index 044c4a10bc4..0c6a3e51457 100644
--- a/gcc/params.opt
+++ b/gcc/params.opt
@@ -138,6 +138,10 @@ Probability that COMDAT function is shared with a
different compilation unit.
Common Joined UInteger Var(param_cxx_max_namespaces_for_diagnostic_help)
Init(1000) Param
Maximum number of namespaces to search for alternatives when name lookup fails.
+-param=dom-jump-threading=
+Common Joined UInteger Var(param_dom_jump_threading) Init(1) IntegerRange(0,
1) Param Optimization
+Enable jump threading in the dominator optimizer pass.
+
-param=dse-max-alias-queries-per-store=
Common Joined UInteger Var(param_dse_max_alias_queries_per_store) Init(256)
Param Optimization
Maximum number of queries into the alias oracle per store.
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/dom-jump-threading-1.c
b/gcc/testsuite/gcc.dg/tree-ssa/dom-jump-threading-1.c
new file mode 100644
index 00000000000..a0d0809b176
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/dom-jump-threading-1.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 --param=dom-jump-threading=0 -fdump-tree-dom2-details
-fdump-tree-optimized" } */
+
+/* Verify that --param=dom-jump-threading=0 keeps DOM from threading
+ jumps. Only DOM can thread a PHI of compares (the backward
+ threader cannot resolve the exit conditional to a single edge), so
+ with the param off the join block and its PHI must survive. */
+
+void g (void);
+
+void
+f (int x, int a, int b, int c, int d)
+{
+ _Bool t;
+ if (x)
+ t = a < b;
+ else
+ t = c < d;
+ if (t)
+ g ();
+}
+
+/* { dg-final { scan-tree-dump-not "Registering jump thread" "dom2" } } */
+/* { dg-final { scan-tree-dump "PHI <" "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/dom-jump-threading-2.c
b/gcc/testsuite/gcc.dg/tree-ssa/dom-jump-threading-2.c
new file mode 100644
index 00000000000..fb6b8a12732
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/dom-jump-threading-2.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-dom2-details" } */
+
+/* Same test as dom-jump-threading-1.c but with DOM jump threading at
+ its default (enabled): DOM must thread the PHI of compares, which
+ keeps the sibling test honest. */
+
+void g (void);
+
+void
+f (int x, int a, int b, int c, int d)
+{
+ _Bool t;
+ if (x)
+ t = a < b;
+ else
+ t = c < d;
+ if (t)
+ g ();
+}
+
+/* { dg-final { scan-tree-dump "Registering jump thread" "dom2" } } */
diff --git a/gcc/tree-ssa-dom.cc b/gcc/tree-ssa-dom.cc
index 02ffcbfc677..7fded792a3c 100644
--- a/gcc/tree-ssa-dom.cc
+++ b/gcc/tree-ssa-dom.cc
@@ -1801,7 +1801,8 @@ dom_opt_dom_walker::before_dom_children (basic_block bb)
void
dom_opt_dom_walker::after_dom_children (basic_block bb)
{
- m_threader->thread_outgoing_edges (bb);
+ if (param_dom_jump_threading)
+ m_threader->thread_outgoing_edges (bb);
bitmap_clear_bit (m_state->get_blocks_on_stack (), bb->index);
m_avail_exprs_stack->pop_to_marker ();
m_const_and_copies->pop_to_marker ();
--
2.47.3
