[PATCH] Control all jump threading passes with -fjump-threads.

[Aldy Hernandez via Gcc-patches]

Last year I mentioned that -fthread-jumps was being ignored by the
majority of our jump threading passes, and Jeff said he'd be in favor
of fixing this.

This patch remedies the situation, but it does change existing behavior.
Currently -fthread-jumps is only enabled for -O2, -O3, and -Os.  This
means that even if we restricted all jump threading passes with
-fthread-jumps, DOM jump threading would still seep through since it
runs at -O1.

I propose this patch, but it does mean that DOM jump threading would
have to be explicitly enabled with -O1 -fthread-jumps.  An
alternative would be to also offer a specific -fno-dom-threading, but
that seems icky.

OK pending tests?

gcc/ChangeLog:

        * tree-ssa-threadbackward.c (pass_thread_jumps::gate): Check
        flag_thread_jumps.
        (pass_early_thread_jumps::gate): Same.
        * tree-ssa-threadedge.c (jump_threader::thread_outgoing_edges):
        Return if !flag_thread_jumps.
        * tree-ssa-threadupdate.c
        (jt_path_registry::register_jump_thread): Assert that
        flag_thread_jumps is true.
---
 gcc/testsuite/gcc.dg/tree-ssa/pr18133-2.c | 2 +-
 gcc/testsuite/gcc.dg/tree-ssa/pr18134.c   | 2 +-
 gcc/tree-ssa-threadbackward.c             | 4 ++--
 gcc/tree-ssa-threadedge.c                 | 3 +++
 gcc/tree-ssa-threadupdate.c               | 2 ++
 5 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr18133-2.c 
b/gcc/testsuite/gcc.dg/tree-ssa/pr18133-2.c
index 8717640e327..1b409852189 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr18133-2.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr18133-2.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O1 -fdump-tree-optimized-blocks" } */
+/* { dg-options "-O1 -fthread-jumps -fdump-tree-optimized-blocks" } */
 
 int c, d;
 
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr18134.c 
b/gcc/testsuite/gcc.dg/tree-ssa/pr18134.c
index cd40ab2c162..d7f5d241eb9 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr18134.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr18134.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O1 -fdump-tree-optimized" } */
+/* { dg-options "-O1 -fthread-jumps -fdump-tree-optimized" } */
 
 int  foo (int a)
 {
diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c
index 95542079faf..8940728cbf2 100644
--- a/gcc/tree-ssa-threadbackward.c
+++ b/gcc/tree-ssa-threadbackward.c
@@ -943,7 +943,7 @@ public:
 bool
 pass_thread_jumps::gate (function *fun ATTRIBUTE_UNUSED)
 {
-  return flag_expensive_optimizations;
+  return flag_thread_jumps && flag_expensive_optimizations;
 }
 
 // Try to thread blocks in FUN.  Return TRUE if any jump thread paths were
@@ -1013,7 +1013,7 @@ public:
 bool
 pass_early_thread_jumps::gate (function *fun ATTRIBUTE_UNUSED)
 {
-  return true;
+  return flag_thread_jumps;
 }
 
 unsigned int
diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c
index ae77e5eb396..e6f0ff0b54b 100644
--- a/gcc/tree-ssa-threadedge.c
+++ b/gcc/tree-ssa-threadedge.c
@@ -1195,6 +1195,9 @@ jump_threader::thread_outgoing_edges (basic_block bb)
   int flags = (EDGE_IGNORE | EDGE_COMPLEX | EDGE_ABNORMAL);
   gimple *last;
 
+  if (!flag_thread_jumps)
+    return;
+
   /* If we have an outgoing edge to a block with multiple incoming and
      outgoing edges, then we may be able to thread the edge, i.e., we
      may be able to statically determine which of the outgoing edges
diff --git a/gcc/tree-ssa-threadupdate.c b/gcc/tree-ssa-threadupdate.c
index 2b9b8f81274..cf96c903668 100644
--- a/gcc/tree-ssa-threadupdate.c
+++ b/gcc/tree-ssa-threadupdate.c
@@ -2822,6 +2822,8 @@ jt_path_registry::cancel_invalid_paths 
(vec<jump_thread_edge *> &path)
 bool
 jt_path_registry::register_jump_thread (vec<jump_thread_edge *> *path)
 {
+  gcc_checking_assert (flag_thread_jumps);
+
   if (!dbg_cnt (registered_jump_thread))
     {
       path->release ();
-- 
2.31.1