package/gcc: add microblaze fix for GCC bug 121432

This is a temporary fix under discussion [1], but it resolves the
problem, by implementing the same behavior as GCC 14.x for register
allocation on Microblaze.

Tested with qemu_microblazeel_mmu_defconfig and used to generate
Microblaze toolchains for the Bootlin toolchains 2025.08-1 [2].

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121432#c10
[2] https://github.com/bootlin/buildroot-toolchains/commit/83947c7bb6158072bc2f52b58e90891cd3dc04a2

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gcc/15.1.0/0003-gcc-config-microblaze-fix-ira-for-GCC15.patch

@@ -0,0 +1,56 @@
+From b6163bbd898e2462455998d5d38fe1463e70ca66 Mon Sep 17 00:00:00 2001
+From: Romain Naour <romain.naour@gmail.com>
+Date: Wed, 6 Aug 2025 22:32:30 +0200
+Subject: [PATCH] gcc/config/microblaze: fix ira for GCC15
+
+Add new hooks for callee-save on microblaze defined by [1] and
+return 1 to restore the old behavior prior to the commit [3].
+
+Tested with qemu_microblazeel_mmu_defconfig and used to generate
+Microblaze toolchains for the Bootlin toolchains 2025.08-1 [4][5].
+
+Upstream: suggested in the bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121432#c10
+
+[1] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b191e8bdecf881d11c1544c441e38f4c18392a15
+[2] https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/i386/i386.cc;h=3128973ba79cccfc6761f451dcb716b9558cc4da;hb=d3ff498c478acefce35de04402f99171b4f64a1a#l20606
+[3] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=3b9b8d6cfdf59337f4b7ce10ce92a98044b2657b
+[4] https://lore.kernel.org/buildroot/87sehzndtp.fsf@dell.be.48ers.dk/T/#mce7decd0b3f6a41008d5de577538a8525c91b374
+[5] https://toolchains.bootlin.com/
+
+Signed-off-by: Romain Naour <romain.naour@gmail.com>
+---
+ gcc/config/microblaze/microblaze.cc | 11 +++++++++++
+ 1 file changed, 11 insertions(+)
+
+diff --git a/gcc/config/microblaze/microblaze.cc b/gcc/config/microblaze/microblaze.cc
+index 4b7f0a1a5e0..3710755ae8d 100644
+--- a/gcc/config/microblaze/microblaze.cc
++++ b/gcc/config/microblaze/microblaze.cc
+@@ -3200,6 +3200,14 @@ microblaze_secondary_reload (bool in_p ATTRIBUTE_UNUSED, rtx x ATTRIBUTE_UNUSED,
+   return NO_REGS;
+ }
+ 
++/* Implement TARGET_CALLEE_SAVE_COST.  */
++static int
++microblaze_callee_save_cost (spill_cost_type, unsigned int hard_regno, machine_mode,
++		       unsigned int, int mem_cost, const HARD_REG_SET &, bool)
++{
++  return 1;
++}
++
+ static void
+ microblaze_globalize_label (FILE * stream, const char *name)
+ {
+@@ -4038,6 +4046,9 @@ microblaze_starting_frame_offset (void)
+ #undef TARGET_SECONDARY_RELOAD
+ #define TARGET_SECONDARY_RELOAD		microblaze_secondary_reload
+ 
++#undef TARGET_CALLEE_SAVE_COST
++#define TARGET_CALLEE_SAVE_COST microblaze_callee_save_cost
++
+ #undef  TARGET_ASM_OUTPUT_MI_THUNK
+ #define TARGET_ASM_OUTPUT_MI_THUNK      microblaze_asm_output_mi_thunk
+ 
+-- 
+2.50.1
+