rtl-ssa: Support for inserting new insns

The upcoming aarch64 load pair pass needs to form store pairs, and can
re-order stores over loads when alias analysis determines this is safe.
In the case that both mem defs have uses in the RTL-SSA IR, and both
stores require re-ordering over their uses, we represent that as
(tentative) deletion of the original store insns and creation of a new
insn, to prevent requiring repeated re-parenting of uses during the
pass.  We then update all mem uses that require re-parenting in one go
at the end of the pass.

To support this, RTL-SSA needs to handle inserting new insns (rather
than just changing existing ones), so this patch adds support for that.

New insns (and new accesses) are temporaries, allocated above a temporary
obstack_watermark, such that the user can easily back out of a change without
awkward bookkeeping.

gcc/ChangeLog:

	* rtl-ssa/accesses.cc (function_info::create_set): New.
	* rtl-ssa/accesses.h (access_info::is_temporary): New.
	* rtl-ssa/changes.cc (move_insn): Handle new (temporary) insns.
	(function_info::finalize_new_accesses): Handle new/temporary
	user-created accesses.
	(function_info::apply_changes_to_insn): Ensure m_is_temp flag
	on new insns gets cleared.
	(function_info::change_insns): Handle new/temporary insns.
	(function_info::create_insn): New.
	* rtl-ssa/changes.h (class insn_change): Make function_info a
	friend class.
	* rtl-ssa/functions.h (function_info): Declare new entry points:
	create_set, create_insn.  Declare new change_alloc helper.
	* rtl-ssa/insns.cc (insn_info::print_full): Identify temporary insns in
	dump.
	* rtl-ssa/insns.h (insn_info): Add new m_is_temp flag and accompanying
	is_temporary accessor.
	* rtl-ssa/internals.inl (insn_info::insn_info): Initialize m_is_temp to
	false.
	* rtl-ssa/member-fns.inl (function_info::change_alloc): New.
	* rtl-ssa/movement.h (restrict_movement_for_defs_ignoring): Add
	handling for temporary defs.

1 files changed, 14 insertions, 0 deletions

diff --git a/gcc/rtl-ssa/functions.h b/gcc/rtl-ssa/functions.h
index ecb40fd..4ffd3fa 100644
--- a/gcc/rtl-ssa/functions.h
+++ b/gcc/rtl-ssa/functions.h
@@ -68,6 +68,16 @@ public:
   // Return the SSA information for CFG_BB.
   bb_info *bb (basic_block cfg_bb) const { return m_bbs[cfg_bb->index]; }
 
+  // Create a temporary def.
+  set_info *create_set (obstack_watermark &watermark,
+			insn_info *insn,
+			resource_info resource);
+
+  // Create a temporary insn with code INSN_CODE and pattern PAT.
+  insn_info *create_insn (obstack_watermark &watermark,
+			  rtx_code insn_code,
+			  rtx pat);
+
   // Return a list of all the instructions in the function, in reverse
   // postorder.  The list includes both real and artificial instructions.
   //
@@ -195,6 +205,10 @@ public:
   // Print the contents of the function to PP.
   void print (pretty_printer *pp) const;
 
+  // Allocate an object of type T above the obstack watermark WM.
+  template<typename T, typename... Ts>
+  T *change_alloc (obstack_watermark &wm, Ts... args);
+
 private:
   class bb_phi_info;
   class build_info;