[gcc r15-1575] fwprop: invoke change_is_worthwhile to judge if a replacement is worthwhile

[HaoChen Gui]

https://gcc.gnu.org/g:ea8061f46a301797e7ba33b52e3b4713fb8e6b48

commit r15-1575-gea8061f46a301797e7ba33b52e3b4713fb8e6b48
Author: Haochen Gui <guihaoc@gcc.gnu.org>
Date:   Mon Jun 24 13:12:51 2024 +0800

    fwprop: invoke change_is_worthwhile to judge if a replacement is worthwhile
    
    gcc/
            * fwprop.cc (try_fwprop_subst_pattern): Invoke change_is_worthwhile
            to judge if a replacement is worthwhile.  Remove single_set check
            and add is_debug_insn check.
            * recog.cc (swap_change): Invalidate recog_data when the cached INSN
            is swapped out.
            * rtl-ssa/changes.cc (rtl_ssa::changes_are_worthwhile): Check if the
            insn cost of new rtl is unknown and fail the replacement.

Diff:
---
 gcc/fwprop.cc          | 37 ++++++++++++++-----------------------
 gcc/recog.cc           |  6 +++++-
 gcc/rtl-ssa/changes.cc |  8 ++++++++
 3 files changed, 27 insertions(+), 24 deletions(-)

diff --git a/gcc/fwprop.cc b/gcc/fwprop.cc
index de543923b92..bfdc7a1b749 100644
--- a/gcc/fwprop.cc
+++ b/gcc/fwprop.cc
@@ -453,7 +453,7 @@ try_fwprop_subst_pattern (obstack_watermark &attempt, insn_change &use_change,
       && (prop.changed_mem_p ()
 	  || contains_mem_rtx_p (src)
 	  || use_insn->is_asm ()
-	  || !single_set (use_rtl)))
+	  || use_insn->is_debug_insn ()))
     {
       if (dump_file && (dump_flags & TDF_DETAILS))
 	fprintf (dump_file, "cannot propagate from insn %d into"
@@ -471,29 +471,20 @@ try_fwprop_subst_pattern (obstack_watermark &attempt, insn_change &use_change,
       redo_changes (0);
     }
 
-  /* ??? In theory, it should be better to use insn costs rather than
-     set_src_costs here.  That would involve replacing this code with
-     change_is_worthwhile.  */
   bool ok = recog (attempt, use_change);
-  if (ok && !prop.changed_mem_p () && !use_insn->is_asm ())
-    if (rtx use_set = single_set (use_rtl))
-      {
-	bool speed = optimize_bb_for_speed_p (BLOCK_FOR_INSN (use_rtl));
-	temporarily_undo_changes (0);
-	auto old_cost = set_src_cost (SET_SRC (use_set),
-				      GET_MODE (SET_DEST (use_set)), speed);
-	redo_changes (0);
-	auto new_cost = set_src_cost (SET_SRC (use_set),
-				      GET_MODE (SET_DEST (use_set)), speed);
-	if (new_cost > old_cost
-	    || (new_cost == old_cost && !prop.likely_profitable_p ()))
-	  {
-	    if (dump_file)
-	      fprintf (dump_file, "change not profitable"
-		       " (cost %d -> cost %d)\n", old_cost, new_cost);
-	    ok = false;
-	  }
-      }
+  if (ok
+      && !prop.changed_mem_p ()
+      && !use_insn->is_asm ()
+      && !use_insn->is_debug_insn ())
+    {
+      bool strict_p = !prop.likely_profitable_p ();
+      if (!change_is_worthwhile (use_change, strict_p))
+	{
+	  if (dump_file)
+	    fprintf (dump_file, "change not profitable");
+	  ok = false;
+	}
+    }
 
   if (!ok)
     {
diff --git a/gcc/recog.cc b/gcc/recog.cc
index a6799e3f5e6..56370e40e01 100644
--- a/gcc/recog.cc
+++ b/gcc/recog.cc
@@ -614,7 +614,11 @@ swap_change (int num)
   else
     std::swap (*changes[num].loc, changes[num].old);
   if (changes[num].object && !MEM_P (changes[num].object))
-    std::swap (INSN_CODE (changes[num].object), changes[num].old_code);
+    {
+      std::swap (INSN_CODE (changes[num].object), changes[num].old_code);
+      if (recog_data.insn == changes[num].object)
+	recog_data.insn = nullptr;
+    }
 }
 
 /* Temporarily undo all the changes numbered NUM and up, with a view
diff --git a/gcc/rtl-ssa/changes.cc b/gcc/rtl-ssa/changes.cc
index 3101f2dc4fc..bc80d7da829 100644
--- a/gcc/rtl-ssa/changes.cc
+++ b/gcc/rtl-ssa/changes.cc
@@ -190,6 +190,14 @@ rtl_ssa::changes_are_worthwhile (array_slice<insn_change *const> changes,
 	  && INSN_CODE (change->rtl ()) != NOOP_MOVE_INSN_CODE)
 	{
 	  change->new_cost = insn_cost (change->rtl (), for_speed);
+	  /* If the cost is unknown, replacement is not worthwhile.  */
+	  if (!change->new_cost)
+	    {
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		fprintf (dump_file,
+			 "Reject replacement due to unknown insn cost.\n");
+	      return false;
+	    }
 	  new_cost += change->new_cost;
 	  if (for_speed)
 	    weighted_new_cost += (cfg_bb->count.to_sreal_scale (entry_count)