From: Kito Cheng <kito.cheng@gmail.com>
To: Philipp Tomsich <philipp.tomsich@vrull.eu>
Cc: Vineet Gupta <vineetg@rivosinc.com>,
GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH v2] RISC-V: bitmanip: improve constant-loading for (1ULL << 31) in DImode
Date: Tue, 7 Jun 2022 18:27:47 +0800 [thread overview]
Message-ID: <CA+yXCZBL_jjyW2O6=S-02R470NKqMtHm1eSmOJe2BQCAcUKLaQ@mail.gmail.com> (raw)
In-Reply-To: <CAAeLtUD6SS4czSLh3ig4LAtCbf=CTuZmU5Cq0cssAri-qHoovQ@mail.gmail.com>
> OK for backport?
OK, it seems no issue after a week :)
>
> On Thu, 2 Jun 2022 at 21:23, Philipp Tomsich <philipp.tomsich@vrull.eu> wrote:
> >
> > Thanks, applied to trunk!
> >
> > On Thu, 2 Jun 2022 at 15:17, Kito Cheng <kito.cheng@gmail.com> wrote:
> > >
> > > LGTM
> > >
> > > On Mon, May 30, 2022 at 5:52 AM Philipp Tomsich
> > > <philipp.tomsich@vrull.eu> wrote:
> > > >
> > > > The SINGLE_BIT_MASK_OPERAND() is overly restrictive, triggering for
> > > > bits above 31 only (to side-step any issues with the negative SImode
> > > > value 0x80000000/(-1ull << 31)/(1 << 31)). This moves the special
> > > > handling of this SImode value (i.e. the check for (-1ull << 31) to
> > > > riscv.cc and relaxes the SINGLE_BIT_MASK_OPERAND() test.
> > > >
> > > > With this, the code-generation for loading (1ULL << 31) from:
> > > > li a0,1
> > > > slli a0,a0,31
> > > > to:
> > > > bseti a0,zero,31
> > > >
> > > > gcc/ChangeLog:
> > > >
> > > > * config/riscv/riscv.cc (riscv_build_integer_1): Rewrite value as
> > > > (-1 << 31) for the single-bit case, when operating on (1 << 31)
> > > > in SImode.
> > > > * gcc/config/riscv/riscv.h (SINGLE_BIT_MASK_OPERAND): Allow for
> > > > any single-bit value, moving the special case for (1 << 31) to
> > > > riscv_build_integer_1 (in riscv.c).
> > > >
> > > > Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
> > > >
> > > > ---
> > > >
> > > > Changes in v2:
> > > > - Use HOST_WIDE_INT_1U/HOST_WIDE_INT_M1U instead of constants.
> > > > - Fix some typos in the comment above the rewrite of the value.
> > > > - Update the comment to clarify that we expect a LUI to be emitted for
> > > > the SImode case (i.e. sign-extended for RV64) of (1 << 31).
> > > >
> > > > gcc/config/riscv/riscv.cc | 9 +++++++++
> > > > gcc/config/riscv/riscv.h | 11 ++++-------
> > > > 2 files changed, 13 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> > > > index f83dc796d88..2e83ca07394 100644
> > > > --- a/gcc/config/riscv/riscv.cc
> > > > +++ b/gcc/config/riscv/riscv.cc
> > > > @@ -420,6 +420,15 @@ riscv_build_integer_1 (struct riscv_integer_op codes[RISCV_MAX_INTEGER_OPS],
> > > > /* Simply BSETI. */
> > > > codes[0].code = UNKNOWN;
> > > > codes[0].value = value;
> > > > +
> > > > + /* RISC-V sign-extends all 32bit values that live in a 32bit
> > > > + register. To avoid paradoxes, we thus need to use the
> > > > + sign-extended (negative) representation (-1 << 31) for the
> > > > + value, if we want to build (1 << 31) in SImode. This will
> > > > + then expand to an LUI instruction. */
> > > > + if (mode == SImode && value == (HOST_WIDE_INT_1U << 31))
> > > > + codes[0].value = (HOST_WIDE_INT_M1U << 31);
> > > > +
> > > > return 1;
> > > > }
> > > >
> > > > diff --git a/gcc/config/riscv/riscv.h b/gcc/config/riscv/riscv.h
> > > > index 5083a1c24b0..6f7f4d3fbdc 100644
> > > > --- a/gcc/config/riscv/riscv.h
> > > > +++ b/gcc/config/riscv/riscv.h
> > > > @@ -528,13 +528,10 @@ enum reg_class
> > > > (((VALUE) | ((1UL<<31) - IMM_REACH)) == ((1UL<<31) - IMM_REACH) \
> > > > || ((VALUE) | ((1UL<<31) - IMM_REACH)) + IMM_REACH == 0)
> > > >
> > > > -/* If this is a single bit mask, then we can load it with bseti. But this
> > > > - is not useful for any of the low 31 bits because we can use addi or lui
> > > > - to load them. It is wrong for loading SImode 0x80000000 on rv64 because it
> > > > - needs to be sign-extended. So we restrict this to the upper 32-bits
> > > > - only. */
> > > > -#define SINGLE_BIT_MASK_OPERAND(VALUE) \
> > > > - (pow2p_hwi (VALUE) && (ctz_hwi (VALUE) >= 32))
> > > > +/* If this is a single bit mask, then we can load it with bseti. Special
> > > > + handling of SImode 0x80000000 on RV64 is done in riscv_build_integer_1. */
> > > > +#define SINGLE_BIT_MASK_OPERAND(VALUE) \
> > > > + (pow2p_hwi (VALUE))
> > > >
> > > > /* Stack layout; function entry, exit and calling. */
> > > >
> > > > --
> > > > 2.34.1
> > > >
next prev parent reply other threads:[~2022-06-07 10:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-29 21:51 Philipp Tomsich
2022-06-02 13:17 ` Kito Cheng
2022-06-02 19:23 ` Philipp Tomsich
2022-06-02 19:24 ` Philipp Tomsich
2022-06-07 10:27 ` Kito Cheng [this message]
2022-06-14 11:18 ` Philipp Tomsich
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