[gcc r17-2598] xtensa: Define LOCAL_REGNO() macro

https://gcc.gnu.org/g:c8c3988ef66c112defe86dcd23e6679d39814587

commit r17-2598-gc8c3988ef66c112defe86dcd23e6679d39814587
Author: Takayuki 'January June' Suwa <[email protected]>
Date:   Sat Jul 18 05:37:13 2026 +0900

    xtensa: Define LOCAL_REGNO() macro
    
    When the Windowed Register Option (TARGET_WINDOWED_ABI) is enabled, and this
    macro is not defined, "phantom" DF livenesses occurs in the function epilogue,
    which can hinder certain optimizations.  Indeed, in the following example,
    the low-overhead loop optimization is rejected because the epilogue BB, which
    succeeds the target loop BB, is incorrectly identified as using the loop
    iterator.
    
         /* example */
         void test(char *q, const char *p, unsigned int n) {
           do
             *q = *p, ++q, ++p;
           while (n-- != 1);
         }
    
         ;; before (-mabi=windowed ; TARGET_LOOPS)
         test:
            entry   sp, 32
            movi.n  a8, 0
         .L2:
            add.n   a9, a3, a8
            l8ui    a10, a9, 0
            add.n   a9, a2, a8
            s8i     a10, a9, 0
            addi.n  a8, a8, 1
            addi.n  a4, a4, -1
            bnez.n  a4, .L2         ;; incorrectly identified as using A4
                                    ;; in the epilogue.
            retw.n
    
    This patch fixes the above issue by properly defining the relevant macro.
    
         ;; after (-mabi=windowed ; TARGET_LOOPS)
         test:
            entry   sp, 32
            movi.n  a8, 0
            loop    a4, .L2_LEND
         .L2:
            add.n   a9, a3, a8
            l8ui    a10, a9, 0
            add.n   a9, a2, a8
            s8i     a10, a9, 0
            addi.n  a8, a8, 1
            .L2_LEND:
            retw.n
    
    gcc/ChangeLog:
    
            * config/xtensa/xtensa.h (LOCAL_REGNO):
            New macro definition.

Diff:
---
 gcc/config/xtensa/xtensa.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/gcc/config/xtensa/xtensa.h b/gcc/config/xtensa/xtensa.h
index 3b33d69bf210..00bb9e06e2e9 100644
--- a/gcc/config/xtensa/xtensa.h
+++ b/gcc/config/xtensa/xtensa.h
@@ -344,6 +344,9 @@ along with GCC; see the file COPYING3.  If not see
      ((unsigned) ((IN) - GP_REG_FIRST) < WINDOW_SIZE)) ?		\
     (IN) + WINDOW_SIZE : (IN)) : (IN))
 
+#define LOCAL_REGNO(REGNO)						\
+  (TARGET_WINDOWED_ABI && GP_REG_P (REGNO)				\
+   && ((unsigned) ((REGNO) - GP_REG_FIRST) < WINDOW_SIZE))
 
 /* Define the classes of registers for register constraints in the
    machine description.  */