[gcc r15-1453] xtensa: Eliminate double MEMW insertions for volatile memory

[Max Filippov]

https://gcc.gnu.org/g:0982552bc4eeffb5520deba10dedecfb2390a8de

commit r15-1453-g0982552bc4eeffb5520deba10dedecfb2390a8de
Author: Takayuki 'January June' Suwa <jjsuwa_sys3175@yahoo.co.jp>
Date:   Wed Jun 19 13:59:54 2024 +0900

    xtensa: Eliminate double MEMW insertions for volatile memory
    
    This patch makes avoid inserting a MEMW instruction before a load/store
    nstruction with volatile memory reference if there is already a MEMW
    immediately before it.
    
    gcc/ChangeLog:
    
            * config/xtensa/xtensa.cc (print_operand):
            When outputting MEMW before the instruction, check if the previous
            instruction is already that.

Diff:
---
 gcc/config/xtensa/xtensa.cc | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/gcc/config/xtensa/xtensa.cc b/gcc/config/xtensa/xtensa.cc
index bc127997ac6c..e2549de5df05 100644
--- a/gcc/config/xtensa/xtensa.cc
+++ b/gcc/config/xtensa/xtensa.cc
@@ -3078,7 +3078,17 @@ print_operand (FILE *file, rtx x, int letter)
 	  /* For a volatile memory reference, emit a MEMW before the
 	     load or store.  */
 	  if (MEM_VOLATILE_P (x) && TARGET_SERIALIZE_VOLATILE)
-	    fprintf (file, "memw\n\t");
+	    {
+	      rtx_insn *prev_insn
+			= prev_nonnote_nondebug_insn (current_output_insn);
+	      rtx pat, src;
+
+	      if (! (prev_insn && NONJUMP_INSN_P (prev_insn)
+		     && GET_CODE (pat = PATTERN (prev_insn)) == SET
+		     && GET_CODE (src = SET_SRC (pat)) == UNSPEC
+		     && XINT (src, 1) == UNSPEC_MEMW))
+		fprintf (file, "memw\n\t");
+	    }
 	}
       else
 	output_operand_lossage ("invalid %%v value");