On 30/11/16 17:32, Wilco Dijkstra wrote:
> Thumb uses a special register allocation order to increase the use of low
> registers. Oddly enough, LR appears before R12, which means that LR must
> be saved and restored even if R12 is available. Swapping R12 and LR means
> this simple example now uses R12 as a temporary (just like ARM):
>
> int f(long long a, long long b)
> {
> if (a < b) return 1;
> return a + b;
> }
>
> cmp r0, r2
> sbcs ip, r1, r3
> ite ge
> addge r0, r0, r2
> movlt r0, #1
> bx lr
>
> Bootstrap OK. CSibe benchmarks unchanged.
>
> ChangeLog:
> 2016-11-30 Wilco Dijkstra <wdijk...@arm.com>
>
> * gcc/config/arm/arm.c (thumb_core_reg_alloc_order): Swap R12 and R14.
>
OK.
R.
> --
> diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
> index
> 43c78f6148a5306fb0079ee2eba12f3763652bcc..29dcefd23762ba861b458b8860eb4b4856a9cb02
> 100644
> --- a/gcc/config/arm/arm.c
> +++ b/gcc/config/arm/arm.c
> @@ -26455,7 +26455,7 @@ arm_mangle_type (const_tree type)
> static const int thumb_core_reg_alloc_order[] =
> {
> 3, 2, 1, 0, 4, 5, 6, 7,
> - 14, 12, 8, 9, 10, 11
> + 12, 14, 8, 9, 10, 11
> };
>
> /* Adjust register allocation order when compiling for Thumb. */
>
