Re: [PATCH] RISC-V: Save/restore ra register correctly [PR112478]

["Christoph Müllner" <christoph.muellner@vrull.eu>]

On Tue, Nov 14, 2023 at 3:15 PM Kito Cheng <kito.cheng@sifive.com> wrote:
>
> We set ra to fixed register now, but we still need to save/restore that at
> prologue/epilogue if that has used.

So before 71f906498ada9 $ra was neither a fixed nor a used register.
Therefore, riscv_save_reg_p returned true in the first test (not global reg,
not used_or_fixed, and ever_live_p).
After this commit, this does not happen anymore, because the test for
not used_or_fixed fails and we don't test for ever_live_p in the following.
And this patch restores this behavior.

Reviewed-by: Christoph Müllner <christoph.muellner@vrull.eu>
Tested-by: Christoph Müllner <christoph.muellner@vrull.eu>

>
> gcc/ChangeLog:
>
>         PR target/112478
>         * config/riscv/riscv.cc (riscv_save_return_addr_reg_p): Check ra
>         is ever lived.
>
> gcc/testsuite/gcc/ChangeLog:
>
>         PR target/112478
>         * riscv/pr112478.c: New.
> ---
>  gcc/config/riscv/riscv.cc                 | 4 ++++
>  gcc/testsuite/gcc.target/riscv/pr112478.c | 8 ++++++++
>  2 files changed, 12 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.target/riscv/pr112478.c
>
> diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> index ecee7eb4727..f09c4066903 100644
> --- a/gcc/config/riscv/riscv.cc
> +++ b/gcc/config/riscv/riscv.cc
> @@ -5802,6 +5802,10 @@ riscv_save_return_addr_reg_p (void)
>    if (riscv_far_jump_used_p ())
>      return true;
>
> +  /* We need to save it if anyone has used that.  */
> +  if (df_regs_ever_live_p (RETURN_ADDR_REGNUM))
> +    return true;
> +
>    /* Need not to use ra for leaf when frame pointer is turned off by
>       option whatever the omit-leaf-frame's value.  */
>    if (frame_pointer_needed && crtl->is_leaf
> diff --git a/gcc/testsuite/gcc.target/riscv/pr112478.c b/gcc/testsuite/gcc.target/riscv/pr112478.c
> new file mode 100644
> index 00000000000..0bbde20b71b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/pr112478.c
> @@ -0,0 +1,8 @@
> +/* { dg-do compile } */
> +/* { dg-options "-ffat-lto-objects" } */
> +
> +void foo() {
> +    asm volatile("# " : ::"ra");
> +}
> +
> +/* { dg-final { scan-assembler "s(w|d)\[ \t\]*ra" } } */
> --
> 2.40.1
>