rtl-ssa: Add replace_nondebug_insn [PR115785]

change_insns is used to change multiple instructions at once, so that
the IR on return is valid & self-consistent.  These changes can involve
moving instructions, and the new position for one instruction might
be expressed in terms of the old position of another instruction
that is changing at the same time.

change_insns therefore adds placeholder instructions to mark each
new instruction position, then replaces each placeholder with the
corresponding real instruction.  This replacement was done in two
steps: removing the old placeholder instruction and inserting the new
real instruction.  But it's more convenient for the upcoming fix for
PR115785 if we do the operation as a single step.  That should also
be slightly more efficient, since e.g. no splay tree operations are
needed.

This operation happens purely on the rtl-ssa instruction chain.
The placeholders are never represented in rtl.

gcc/
	PR rtl-optimization/115785
	* rtl-ssa/functions.h (function_info::replace_nondebug_insn): Declare.
	* rtl-ssa/insns.h (insn_info::order_node::set_uid): New function.
	(insn_info::remove_note): Declare.
	* rtl-ssa/insns.cc (insn_info::remove_note): New function.
	(function_info::replace_nondebug_insn): Likewise.
	* rtl-ssa/changes.cc (function_info::change_insns): Use
	replace_nondebug_insn instead of remove_insn + add_insn.

4 files changed, 48 insertions, 4 deletions

diff --git a/gcc/rtl-ssa/changes.cc b/gcc/rtl-ssa/changes.cc
index bc80d7d..6b6f7cd 100644
--- a/gcc/rtl-ssa/changes.cc
+++ b/gcc/rtl-ssa/changes.cc
@@ -874,14 +874,11 @@ function_info::change_insns (array_slice<insn_change *> changes)
 	    }
 	  else
 	    {
-	      // Remove the placeholder first so that we have a wider range of
-	      // program points when inserting INSN.
 	      insn_info *after = placeholder->prev_any_insn ();
 	      if (!insn->is_temporary ())
 		remove_insn (insn);
-	      remove_insn (placeholder);
+	      replace_nondebug_insn (placeholder, insn);
 	      insn->set_bb (after->bb ());
-	      add_insn_after (insn, after);
 	    }
 	}
     }
diff --git a/gcc/rtl-ssa/functions.h b/gcc/rtl-ssa/functions.h
index e213462..8be04f1 100644
--- a/gcc/rtl-ssa/functions.h
+++ b/gcc/rtl-ssa/functions.h
@@ -274,6 +274,7 @@ private:
   insn_info::order_node *need_order_node (insn_info *);
 
   void add_insn_after (insn_info *, insn_info *);
+  void replace_nondebug_insn (insn_info *, insn_info *);
   void append_insn (insn_info *);
   void remove_insn (insn_info *);
 
diff --git a/gcc/rtl-ssa/insns.cc b/gcc/rtl-ssa/insns.cc
index 68365e3..7e26bfd 100644
--- a/gcc/rtl-ssa/insns.cc
+++ b/gcc/rtl-ssa/insns.cc
@@ -70,6 +70,16 @@ insn_info::add_note (insn_note *note)
   *ptr = note;
 }
 
+// Remove NOTE from the instruction's notes.
+void
+insn_info::remove_note (insn_note *note)
+{
+  insn_note **ptr = &m_first_note;
+  while (*ptr != note)
+    ptr = &(*ptr)->m_next_note;
+  *ptr = note->m_next_note;
+}
+
 // Implement compare_with for the case in which this insn and OTHER
 // have the same program point.
 int
@@ -346,6 +356,38 @@ function_info::add_insn_after (insn_info *insn, insn_info *after)
     }
 }
 
+// Replace non-debug instruction OLD_INSN with non-debug instruction NEW_INSN.
+// NEW_INSN is not currently linked.
+void
+function_info::replace_nondebug_insn (insn_info *old_insn, insn_info *new_insn)
+{
+  gcc_assert (!old_insn->is_debug_insn ()
+	      && !new_insn->is_debug_insn ()
+	      && !new_insn->has_insn_links ());
+
+  insn_info *prev = old_insn->prev_any_insn ();
+  insn_info *next_nondebug = old_insn->next_nondebug_insn ();
+
+  // We should never remove the entry or exit block's instructions.
+  gcc_checking_assert (prev && next_nondebug);
+
+  new_insn->copy_prev_from (old_insn);
+  new_insn->copy_next_from (old_insn);
+
+  prev->set_next_any_insn (new_insn);
+  next_nondebug->set_prev_sametype_insn (new_insn);
+
+  new_insn->set_point (old_insn->point ());
+  if (insn_info::order_node *order = old_insn->get_order_node ())
+    {
+      order->set_uid (new_insn->uid ());
+      old_insn->remove_note (order);
+      new_insn->add_note (order);
+    }
+
+  old_insn->clear_insn_links ();
+}
+
 // Remove INSN from the function's list of instructions.
 void
 function_info::remove_insn (insn_info *insn)
diff --git a/gcc/rtl-ssa/insns.h b/gcc/rtl-ssa/insns.h
index 1ba56ab..80eae5e 100644
--- a/gcc/rtl-ssa/insns.h
+++ b/gcc/rtl-ssa/insns.h
@@ -330,6 +330,9 @@ private:
     // Return the uid of the instruction that this node describes.
     int uid () const { return m_data32; }
 
+    // Change the uid of the instruction that this node describes.
+    void set_uid (int uid) { m_data32 = uid; }
+
     // The splay tree pointers.
     order_node *m_children[2];
     order_node *m_parent;
@@ -374,6 +377,7 @@ private:
   void set_bb (bb_info *bb) { m_bb = bb; }
 
   void add_note (insn_note *note);
+  void remove_note (insn_note *note);
 
   order_node *get_order_node () const;
   order_node *get_known_order_node () const;