Xi Ruoyao <xry...@mengyan1223.wang> writes:
> Bootstrapped and regtested on mips64el-linux-gnuabi64.
>
> I'm not sure if it's "correct" to clobber other registers during the
> zeroing of scratch registers. But I can't really come up with a better
> idea: on MIPS there is no simple way to clear one bit in FCSR (i. e.
> FCC[x]). We can't just use "c.f.s $fccx,$f0,$f0" because it will raise
> an exception if $f0 contains a sNaN.
Yeah, it's a bit of a grey area, but I think it should be fine, provided
that the extra clobbers are never used as return registers (which is
obviously true for the FCC registers).
But on that basis…
> +static HARD_REG_SET
> +mips_zero_call_used_regs (HARD_REG_SET need_zeroed_hardregs)
> +{
> + HARD_REG_SET zeroed_hardregs;
> + CLEAR_HARD_REG_SET (zeroed_hardregs);
> +
> + if (TEST_HARD_REG_BIT (need_zeroed_hardregs, HI_REGNUM))
> + {
> + /* Clear HI and LO altogether. MIPS target treats HILO as a
> + double-word register. */
> + machine_mode dword_mode = TARGET_64BIT ? TImode : DImode;
> + rtx hilo = gen_rtx_REG (dword_mode, MD_REG_FIRST);
> + rtx zero = CONST0_RTX (dword_mode);
> + emit_move_insn (hilo, zero);
> +
> + SET_HARD_REG_BIT (zeroed_hardregs, HI_REGNUM);
> + if (TEST_HARD_REG_BIT (need_zeroed_hardregs, LO_REGNUM))
> + SET_HARD_REG_BIT (zeroed_hardregs, LO_REGNUM);
> + else
> + emit_clobber (gen_rtx_REG (word_mode, LO_REGNUM));
…I don't think this conditional LO_REGNUM code is worth it.
We might as well just add both registers to zeroed_hardregs.
> + }
> +
> + bool zero_fcc = false;
> + for (int i = ST_REG_FIRST; i <= ST_REG_LAST; i++)
> + if (TEST_HARD_REG_BIT (need_zeroed_hardregs, i))
> + zero_fcc = true;
> +
> + /* MIPS does not have a simple way to clear one bit in FCC. We just
> + clear FCC with ctc1 and clobber all FCC bits. */
> + if (zero_fcc)
> + {
> + emit_insn (gen_mips_zero_fcc ());
> + for (int i = ST_REG_FIRST; i <= ST_REG_LAST; i++)
> + if (TEST_HARD_REG_BIT (need_zeroed_hardregs, i))
> + SET_HARD_REG_BIT (zeroed_hardregs, i);
> + else
> + emit_clobber (gen_rtx_REG (CCmode, i));
> + }
Here too I think we should just do:
zeroed_hardregs |= reg_class_contents[ST_REGS] & accessible_reg_set;
to include all available FCC registers.
> +
> + need_zeroed_hardregs &= ~zeroed_hardregs;
> + return zeroed_hardregs |
> + default_zero_call_used_regs (need_zeroed_hardregs);
Nit, but: should be formatted as:
return (zeroed_hardregs
| default_zero_call_used_regs (need_zeroed_hardregs));
> +}
> +
>
> /* Initialize the GCC target structure. */
> #undef TARGET_ASM_ALIGNED_HI_OP
> @@ -22919,6 +22964,8 @@ mips_asm_file_end (void)
> #undef TARGET_ASM_FILE_END
> #define TARGET_ASM_FILE_END mips_asm_file_end
>
> +#undef TARGET_ZERO_CALL_USED_REGS
> +#define TARGET_ZERO_CALL_USED_REGS mips_zero_call_used_regs
>
> struct gcc_target targetm = TARGET_INITIALIZER;
>
> diff --git a/gcc/config/mips/mips.md b/gcc/config/mips/mips.md
> index e0f0a582732..edf58710cdd 100644
> --- a/gcc/config/mips/mips.md
> +++ b/gcc/config/mips/mips.md
> @@ -96,6 +96,7 @@ (define_c_enum "unspec" [
> ;; Floating-point environment.
> UNSPEC_GET_FCSR
> UNSPEC_SET_FCSR
> + UNSPEC_ZERO_FCC
>
> ;; HI/LO moves.
> UNSPEC_MFHI
> @@ -7670,6 +7671,11 @@ (define_insn "*mips_set_fcsr"
> "TARGET_HARD_FLOAT"
> "ctc1\t%0,$31")
>
> +(define_insn "mips_zero_fcc"
> + [(unspec_volatile [(const_int 0)] UNSPEC_ZERO_FCC)]
> + "TARGET_HARD_FLOAT"
> + "ctc1\t$0,$25")
I've forgotten a lot of MIPS stuff, so: does this clear only the
FCC registers, or does it clear other things (such as exception bits)
as well? Does it work even for !ISA_HAS_8CC?
I think this pattern should explicit clear all eight registers, e.g. using:
(set (reg:CC FCC0_REGNUM) (const_int 0))
(set (reg:CC FCC1_REGNUM) (const_int 0))
…
which unfortunately means defining 8 new register constants in mips.md.
I guess for extra safety there should be a separate !ISA_HAS_8CC version
that only sets FCC0_REGNUM.
An alternative would be to avoid clearing the FCC registers altogether.
I suppose that's less secure, but residual information could leak through
the exception bits as well, and it isn't clear whether those should be
zeroed at the end of each function. I guess it depends on people's
appetite for risk.
Both ways are OK with me, just mentioning it in case.
Thanks,
Richard
> +
> ;; See tls_get_tp_mips16_<mode> for why this form is used.
> (define_insn "mips_set_fcsr_mips16_<mode>"
> [(unspec_volatile:SI [(match_operand:P 0 "call_insn_operand" "dS")
> diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-10.c
> b/gcc/testsuite/c-c++-common/zero-scratch-regs-10.c
> index 96e0b79b328..c23b2ceb391 100644
> --- a/gcc/testsuite/c-c++-common/zero-scratch-regs-10.c
> +++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-10.c
> @@ -1,5 +1,5 @@
> /* { dg-do run } */
> -/* { dg-skip-if "not implemented" { ! { i?86*-*-* x86_64*-*-* sparc*-*-*
> aarch64*-*-* nvptx*-*-* s390*-*-* } } } */
> +/* { dg-skip-if "not implemented" { ! { i?86*-*-* x86_64*-*-* sparc*-*-*
> aarch64*-*-* nvptx*-*-* s390*-*-* mips*-*-* } } } */
> /* { dg-options "-O2" } */
>
> #include <assert.h>
> diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-11.c
> b/gcc/testsuite/c-c++-common/zero-scratch-regs-11.c
> index 0714f95a04f..f51f5a2161c 100644
> --- a/gcc/testsuite/c-c++-common/zero-scratch-regs-11.c
> +++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-11.c
> @@ -1,5 +1,5 @@
> /* { dg-do run } */
> -/* { dg-skip-if "not implemented" { ! { i?86*-*-* x86_64*-*-* sparc*-*-*
> aarch64*-*-* arm*-*-* nvptx*-*-* s390*-*-* } } } */
> +/* { dg-skip-if "not implemented" { ! { i?86*-*-* x86_64*-*-* sparc*-*-*
> aarch64*-*-* arm*-*-* nvptx*-*-* s390*-*-* mips*-*-* } } } */
> /* { dg-options "-O2 -fzero-call-used-regs=all" } */
>
> #include "zero-scratch-regs-10.c"
> diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-8.c
> b/gcc/testsuite/c-c++-common/zero-scratch-regs-8.c
> index aceda7e5cb8..3e5e59b3c79 100644
> --- a/gcc/testsuite/c-c++-common/zero-scratch-regs-8.c
> +++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-8.c
> @@ -1,5 +1,5 @@
> /* { dg-do run } */
> -/* { dg-skip-if "not implemented" { ! { i?86*-*-* x86_64*-*-* sparc*-*-*
> aarch64*-*-* arm*-*-* nvptx*-*-* s390*-*-* } } } */
> +/* { dg-skip-if "not implemented" { ! { i?86*-*-* x86_64*-*-* sparc*-*-*
> aarch64*-*-* arm*-*-* nvptx*-*-* s390*-*-* mips*-*-* } } } */
> /* { dg-options "-O2 -fzero-call-used-regs=all-arg" } */
>
> #include "zero-scratch-regs-1.c"
> diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-9.c
> b/gcc/testsuite/c-c++-common/zero-scratch-regs-9.c
> index f3152a7a732..d88d61accb2 100644
> --- a/gcc/testsuite/c-c++-common/zero-scratch-regs-9.c
> +++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-9.c
> @@ -1,5 +1,5 @@
> /* { dg-do run } */
> -/* { dg-skip-if "not implemented" { ! { i?86*-*-* x86_64*-*-* sparc*-*-*
> aarch64*-*-* arm*-*-* nvptx*-*-* s390*-*-* } } } */
> +/* { dg-skip-if "not implemented" { ! { i?86*-*-* x86_64*-*-* sparc*-*-*
> aarch64*-*-* arm*-*-* nvptx*-*-* s390*-*-* mips*-*-* } } } */
> /* { dg-options "-O2 -fzero-call-used-regs=all" } */
>
> #include "zero-scratch-regs-1.c"
