[gcc(refs/users/aoliva/heads/testme)] [lra] take scratch as implicit unused output reloads [PR55212]

[Alexandre Oliva]

https://gcc.gnu.org/g:04bd6f2a933dbffcf769f39dcacb973436b1ebb3

commit 04bd6f2a933dbffcf769f39dcacb973436b1ebb3
Author: Alexandre Oliva <oliva@gnu.org>
Date:   Wed Dec 17 02:44:32 2025 -0300

    [lra] take scratch as implicit unused output reloads [PR55212]
    
    When trying to convert the SH port to use LRA, the first issue I hit
    was the need for dealing with former scratch registers at places we
    didn't need to on other ports, treating them like unused output
    reloads instead of rejecting them.
    
    
    for  gcc/ChangeLog
    
            PR target/55212
            * lra-constraints.cc (match_reload): Treat former scratch
            regs as implicit unused output reloads.
            (process_alt_operands): Likewise.
            (curr_insn_transform): Likewise.

Diff:
---
 gcc/lra-constraints.cc | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index 66a300bf268b..910f3fba8f47 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -1243,7 +1243,9 @@ match_reload (signed char out, signed char *ins, signed char *outs,
     return;
   /* See a comment for the input operand above.  */
   narrow_reload_pseudo_class (out_rtx, goal_class);
-  if (find_reg_note (curr_insn, REG_UNUSED, out_rtx) == NULL_RTX)
+  if (find_reg_note (curr_insn, REG_UNUSED, out_rtx) == NULL_RTX
+      && !ira_former_scratch_p (REGNO (SUBREG_P (out_rtx)
+				       ? SUBREG_REG (out_rtx) : out_rtx)))
     {
       reg = SUBREG_P (out_rtx) ? SUBREG_REG (out_rtx) : out_rtx;
       start_sequence ();
@@ -3002,7 +3004,8 @@ process_alt_operands (int only_alternative)
 		 objects with a REG_UNUSED note.  */
 	      if ((curr_static_id->operand[nop].type != OP_IN
 		   && no_output_reloads_p
-		   && ! find_reg_note (curr_insn, REG_UNUSED, op))
+		   && ! find_reg_note (curr_insn, REG_UNUSED, op)
+		   && ! scratch_p)
 		  || (curr_static_id->operand[nop].type != OP_OUT
 		      && no_input_reloads_p && ! const_to_mem)
 		  || (this_alternative_matches >= 0
@@ -3012,7 +3015,8 @@ process_alt_operands (int only_alternative)
 				  [this_alternative_matches].type != OP_IN)
 			      && ! find_reg_note (curr_insn, REG_UNUSED,
 						  no_subreg_reg_operand
-						  [this_alternative_matches])))))
+						  [this_alternative_matches])
+			      && ! scratch_p))))
 		{
 		  if (lra_dump_file != NULL)
 		    fprintf
@@ -4856,7 +4860,8 @@ curr_insn_transform (bool check_only_p)
 	  if (type != OP_IN
 	      && find_reg_note (curr_insn, REG_UNUSED, old) == NULL_RTX
 	      /* OLD can be an equivalent constant here.  */
-	      && !CONSTANT_P (old))
+	      && !CONSTANT_P (old)
+	      && !ira_former_scratch_p (REGNO (old)))
 	    {
 	      start_sequence ();
 	      lra_emit_move (type == OP_INOUT ? copy_rtx (old) : old, new_reg);