On 16/10/15 15:36, Jiong Wang wrote:
> The patch https://gcc.gnu.org/ml/gcc-patches/2014-09/msg02654.html
> from last year changed the definition of LR in CALL_USED_REGISTERS,
> but didn't update the comment above the #define to reflect the new usage.
>
> This patch bring the comment inline with the implementation.
>
> OK for trunk?
>
> Thanks.
>
> 2015-10-16 Jiong. Wang <[email protected]>
>
> gcc/
> * config/aarch64/aarch64.h: Update the comments on usage of X30.
>
>
> fix-comment.patch
>
>
> diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
> index 5a8db76..1eaaca0 100644
> --- a/gcc/config/aarch64/aarch64.h
> +++ b/gcc/config/aarch64/aarch64.h
> @@ -210,14 +210,17 @@ extern unsigned aarch64_architecture_version;
> significant bits. Unlike AArch32 S1 is not packed into D0,
> etc. */
>
> -/* Note that we don't mark X30 as a call-clobbered register. The idea is
> - that it's really the call instructions themselves which clobber X30.
> - We don't care what the called function does with it afterwards.
> -
> - This approach makes it easier to implement sibcalls. Unlike normal
> - calls, sibcalls don't clobber X30, so the register reaches the
> - called function intact. EPILOGUE_USES says that X30 is useful
> - to the called function. */
> +/* We don't mark X30 as a fixed register while we mark it as a caller-saved
> + register. The idea is we want X30 to be allocable as a caller-saved
> + register when possible.
> +
> + NOTE: although X30 is marked as caller-saved, it's callee-saved at the
> same
> + time. The caller-saved attribute makes sure if X30 is allocated as free
> + register to hold any temporary value then the value is saved properly
> across
> + function call. While on AArch64, the call instruction writes the return
> + address to LR. If the called function is a non-leaf function, it is the
> + responsibility of the callee to save and restore LR appropriately in it's
> + prologue / epilogue. */
>
Sorry, but I find that just confusing.
Wouldn't it be easier just to say:
X30 is clobbered by call instructions, so must be treated as a
caller-saved register.
I don't think there's anything more to add after that.
R.
> #define FIXED_REGISTERS \
> { \
>
