[PATCH 1/2] xtensa: Define HONOR_REG_ALLOC_ORDER as 1

[Takayuki 'January June' Suwa]

Since the commit of the preceding patch for IRA, "ira: Scale save/restore
costs of callee save registers with block frequency" 
(3b9b8d6cfdf59337f4b7ce10ce92a98044b2657b),
the Xtensa ISA has shown a tendency to allocate slightly more function stack
frames, especially when using the CALL0 ABI.
    /* example */
    extern void foo(void);
    int test(int a) {
      int array[252];
      foo();
      asm volatile (""::"m"(array));
      return a;
    }

    ;; before (-O2 -mabi=call0)
    test:
        addi    sp, sp, -16
        s32i.n  a0, sp, 12
        addmi   sp, sp, -0x400
        s32i    a2, sp, 1008
        call0   foo
        l32i    a2, sp, 1008
        addmi   sp, sp, 0x400
        l32i.n  a0, sp, 12
        addi    sp, sp, 16
        ret.n

This patch disables the incorrect register save cost estimation in function
prologues/epilogues by defining the HONOR_REG_ALLOC_ORDER macro as 1.

    ;; after (-O2 -mabi=call0)
    test:
        addmi   sp, sp, -0x400
        s32i    a0, sp, 1020
        s32i    a2, sp, 1016
        call0   foo
        l32i    a2, sp, 1016
        l32i    a0, sp, 1020
        addmi   sp, sp, 0x400
        ret.n

gcc/ChangeLog:

        * config/xtensa/xtensa.h (HONOR_REG_ALLOC_ORDER):
        New macro definition.

gcc/testsuite/ChangeLog:

        * gcc.target/xtensa/elim_callee_saved.c:
        Revise the test item for the number of mov instructions in the
        assembler output.
---
 gcc/config/xtensa/xtensa.h                          | 4 ++++
 gcc/testsuite/gcc.target/xtensa/elim_callee_saved.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/gcc/config/xtensa/xtensa.h b/gcc/config/xtensa/xtensa.h
index 2bf43f7af42..3b33d69bf21 100644
--- a/gcc/config/xtensa/xtensa.h
+++ b/gcc/config/xtensa/xtensa.h
@@ -254,6 +254,10 @@ along with GCC; see the file COPYING3.  If not see
 }
 #define ADJUST_REG_ALLOC_ORDER xtensa_adjust_reg_alloc_order ()
 
+/* Tell IRA to use the order we define rather than messing it up with its
+   own cost calculations.  */
+#define HONOR_REG_ALLOC_ORDER 1
+
 /* Internal macros to classify a register number.  */
 
 /* 16 address registers + fake registers */
diff --git a/gcc/testsuite/gcc.target/xtensa/elim_callee_saved.c 
b/gcc/testsuite/gcc.target/xtensa/elim_callee_saved.c
index cd3d6b9f249..69e5be35dfd 100644
--- a/gcc/testsuite/gcc.target/xtensa/elim_callee_saved.c
+++ b/gcc/testsuite/gcc.target/xtensa/elim_callee_saved.c
@@ -34,5 +34,5 @@ int __attribute__((optimize(0))) test3(int a) {
   return bar() + a;
 }
 
-/* { dg-final { scan-assembler-times "mov\t|mov.n\t" 21 } } */
+/* { dg-final { scan-assembler-times "mov\t|mov.n\t" 20 } } */
 /* { dg-final { scan-assembler-times "a15, 8" 2 } } */
--
2.39.5