Re: [PATCH] RISC-V: Fix bug that XTheadMemPair extension caused fcsr not to be saved and restored before and after interrupt.

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

On Fri, Nov 10, 2023 at 8:14 AM Jin Ma <jinma@linux.alibaba.com> wrote:
>
> The t0 register is used as a temporary register for interrupts, so it needs
> special treatment. It is necessary to avoid using "th.ldd" in the interrupt
> program to stop the subsequent operation of the t0 register, so they need to
> exchange positions in the function "riscv_for_each_saved_reg".

RISCV_PROLOGUE_TEMP_REGNUM needs indeed to be treated special
in case of ISRs and fcsr. This patch just moves the TARGET_XTHEADMEMPAIR
block after the ISR/fcsr block.

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

>
> gcc/ChangeLog:
>
>         * config/riscv/riscv.cc (riscv_for_each_saved_reg): Place the interrupt
>         operation before the XTheadMemPair.
> ---
>  gcc/config/riscv/riscv.cc                     | 56 +++++++++----------
>  .../riscv/xtheadmempair-interrupt-fcsr.c      | 18 ++++++
>  2 files changed, 46 insertions(+), 28 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/riscv/xtheadmempair-interrupt-fcsr.c
>
> diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> index e25692b86fc..fa2d4d4b779 100644
> --- a/gcc/config/riscv/riscv.cc
> +++ b/gcc/config/riscv/riscv.cc
> @@ -6346,6 +6346,34 @@ riscv_for_each_saved_reg (poly_int64 sp_offset, riscv_save_restore_fn fn,
>           && riscv_is_eh_return_data_register (regno))
>         continue;
>
> +      /* In an interrupt function, save and restore some necessary CSRs in the stack
> +        to avoid changes in CSRs.  */
> +      if (regno == RISCV_PROLOGUE_TEMP_REGNUM
> +         && cfun->machine->interrupt_handler_p
> +         && ((TARGET_HARD_FLOAT  && cfun->machine->frame.fmask)
> +             || (TARGET_ZFINX
> +                 && (cfun->machine->frame.mask & ~(1 << RISCV_PROLOGUE_TEMP_REGNUM)))))
> +       {
> +         unsigned int fcsr_size = GET_MODE_SIZE (SImode);
> +         if (!epilogue)
> +           {
> +             riscv_save_restore_reg (word_mode, regno, offset, fn);
> +             offset -= fcsr_size;
> +             emit_insn (gen_riscv_frcsr (RISCV_PROLOGUE_TEMP (SImode)));
> +             riscv_save_restore_reg (SImode, RISCV_PROLOGUE_TEMP_REGNUM,
> +                                     offset, riscv_save_reg);
> +           }
> +         else
> +           {
> +             riscv_save_restore_reg (SImode, RISCV_PROLOGUE_TEMP_REGNUM,
> +                                     offset - fcsr_size, riscv_restore_reg);
> +             emit_insn (gen_riscv_fscsr (RISCV_PROLOGUE_TEMP (SImode)));
> +             riscv_save_restore_reg (word_mode, regno, offset, fn);
> +             offset -= fcsr_size;
> +           }
> +         continue;
> +       }
> +
>        if (TARGET_XTHEADMEMPAIR)
>         {
>           /* Get the next reg/offset pair.  */
> @@ -6376,34 +6404,6 @@ riscv_for_each_saved_reg (poly_int64 sp_offset, riscv_save_restore_fn fn,
>             }
>         }
>
> -      /* In an interrupt function, save and restore some necessary CSRs in the stack
> -        to avoid changes in CSRs.  */
> -      if (regno == RISCV_PROLOGUE_TEMP_REGNUM
> -         && cfun->machine->interrupt_handler_p
> -         && ((TARGET_HARD_FLOAT  && cfun->machine->frame.fmask)
> -             || (TARGET_ZFINX
> -                 && (cfun->machine->frame.mask & ~(1 << RISCV_PROLOGUE_TEMP_REGNUM)))))
> -       {
> -         unsigned int fcsr_size = GET_MODE_SIZE (SImode);
> -         if (!epilogue)
> -           {
> -             riscv_save_restore_reg (word_mode, regno, offset, fn);
> -             offset -= fcsr_size;
> -             emit_insn (gen_riscv_frcsr (RISCV_PROLOGUE_TEMP (SImode)));
> -             riscv_save_restore_reg (SImode, RISCV_PROLOGUE_TEMP_REGNUM,
> -                                     offset, riscv_save_reg);
> -           }
> -         else
> -           {
> -             riscv_save_restore_reg (SImode, RISCV_PROLOGUE_TEMP_REGNUM,
> -                                     offset - fcsr_size, riscv_restore_reg);
> -             emit_insn (gen_riscv_fscsr (RISCV_PROLOGUE_TEMP (SImode)));
> -             riscv_save_restore_reg (word_mode, regno, offset, fn);
> -             offset -= fcsr_size;
> -           }
> -         continue;
> -       }
> -
>        riscv_save_restore_reg (word_mode, regno, offset, fn);
>      }
>
> diff --git a/gcc/testsuite/gcc.target/riscv/xtheadmempair-interrupt-fcsr.c b/gcc/testsuite/gcc.target/riscv/xtheadmempair-interrupt-fcsr.c
> new file mode 100644
> index 00000000000..d06f05f5c7c
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/xtheadmempair-interrupt-fcsr.c
> @@ -0,0 +1,18 @@
> +/* Verify that fcsr instructions emitted.  */
> +/* { dg-do compile } */
> +/* { dg-require-effective-target hard_float } */
> +/* { dg-skip-if "" { *-*-* } { "-O0" "-O1" "-g" "-Oz" "-Os" "-flto" } } */
> +/* { dg-options "-march=rv64gc_xtheadmempair -mtune=thead-c906 -funwind-tables" { target { rv64 } } } */
> +/* { dg-options "-march=rv32gc_xtheadmempair -mtune=thead-c906 -funwind-tables" { target { rv32 } } } */
> +
> +
> +extern int foo (void);
> +
> +void __attribute__ ((interrupt))
> +sub (void)
> +{
> +  foo ();
> +}
> +
> +/* { dg-final { scan-assembler-times "frcsr\t" 1 } } */
> +/* { dg-final { scan-assembler-times "fscsr\t" 1 } } */
>
> base-commit: e7f4040d9d6ec40c48ada940168885d7dde03af9
> --
> 2.17.1
>