"H.J. Lu" <hjl.to...@gmail.com> writes:
> On Wed, May 25, 2022 at 12:30 AM Richard Sandiford
> <richard.sandif...@arm.com> wrote:
>>
>> "H.J. Lu via Gcc-patches" <gcc-patches@gcc.gnu.org> writes:
>> > On Mon, May 23, 2022 at 12:38:06PM +0200, Richard Biener wrote:
>> >> On Sat, May 21, 2022 at 5:02 AM H.J. Lu via Gcc-patches
>> >> <gcc-patches@gcc.gnu.org> wrote:
>> >> >
>> >> > When recording store for RTL dead store elimination, check if the source
>> >> > register is set only once to a constant. If yes, record the constant
>> >> > as the store source. It eliminates unrolled zero stores after memset 0
>> >> > in a loop where a vector register is used as the zero store source.
>> >> >
>> >> > gcc/
>> >> >
>> >> > PR rtl-optimization/105638
>> >> > * dse.cc (record_store): Use the constant source if the source
>> >> > register is set only once.
>> >> >
>> >> > gcc/testsuite/
>> >> >
>> >> > PR rtl-optimization/105638
>> >> > * g++.target/i386/pr105638.C: New test.
>> >> > ---
>> >> > gcc/dse.cc | 19 ++++++++++
>> >> > gcc/testsuite/g++.target/i386/pr105638.C | 44 ++++++++++++++++++++++++
>> >> > 2 files changed, 63 insertions(+)
>> >> > create mode 100644 gcc/testsuite/g++.target/i386/pr105638.C
>> >> >
>> >> > diff --git a/gcc/dse.cc b/gcc/dse.cc
>> >> > index 30c11cee034..0433dd3d846 100644
>> >> > --- a/gcc/dse.cc
>> >> > +++ b/gcc/dse.cc
>> >> > @@ -1508,6 +1508,25 @@ record_store (rtx body, bb_info_t bb_info)
>> >> >
>> >> > if (tem && CONSTANT_P (tem))
>> >> > const_rhs = tem;
>> >> > + else
>> >> > + {
>> >> > + /* If RHS is set only once to a constant, set CONST_RHS
>> >> > + to the constant. */
>> >> > + df_ref def = DF_REG_DEF_CHAIN (REGNO (rhs));
>> >> > + if (def != nullptr
>> >> > + && !DF_REF_IS_ARTIFICIAL (def)
>> >> > + && !DF_REF_NEXT_REG (def))
>> >> > + {
>> >> > + rtx_insn *def_insn = DF_REF_INSN (def);
>> >> > + rtx def_body = PATTERN (def_insn);
>> >> > + if (GET_CODE (def_body) == SET)
>> >> > + {
>> >> > + rtx def_src = SET_SRC (def_body);
>> >> > + if (CONSTANT_P (def_src))
>> >> > + const_rhs = def_src;
>> >>
>> >> doesn't DSE have its own tracking of stored values? Shouldn't we
>> >
>> > It tracks stored values only within the basic block. When RTL loop
>> > invariant motion hoists a constant initialization out of the loop into
>> > a separate basic block, the constant store value becomes unknown
>> > within the original basic block.
>> >
>> >> improve _that_ if it is not enough? I also wonder if you need to
>> >
>> > My patch extends DSE stored value tracking to include the constant which
>> > is set only once in another basic block.
>> >
>> >> verify the SET isn't partial?
>> >>
>> >
>> > Here is the v2 patch to check that the constant is set by a non-partial
>> > unconditional load.
>> >
>> > OK for master?
>> >
>> > Thanks.
>> >
>> > H.J.
>> > ---
>> > RTL DSE tracks redundant constant stores within a basic block. When RTL
>> > loop invariant motion hoists a constant initialization out of the loop
>> > into a separate basic block, the constant store value becomes unknown
>> > within the original basic block. When recording store for RTL DSE, check
>> > if the source register is set only once to a constant by a non-partial
>> > unconditional load. If yes, record the constant as the constant store
>> > source. It eliminates unrolled zero stores after memset 0 in a loop
>> > where a vector register is used as the zero store source.
>> >
>> > gcc/
>> >
>> > PR rtl-optimization/105638
>> > * dse.cc (record_store): Use the constant source if the source
>> > register is set only once.
>> >
>> > gcc/testsuite/
>> >
>> > PR rtl-optimization/105638
>> > * g++.target/i386/pr105638.C: New test.
>> > ---
>> > gcc/dse.cc | 22 ++++++++++++
>> > gcc/testsuite/g++.target/i386/pr105638.C | 44 ++++++++++++++++++++++++
>> > 2 files changed, 66 insertions(+)
>> > create mode 100644 gcc/testsuite/g++.target/i386/pr105638.C
>> >
>> > diff --git a/gcc/dse.cc b/gcc/dse.cc
>> > index 30c11cee034..af8e88dac32 100644
>> > --- a/gcc/dse.cc
>> > +++ b/gcc/dse.cc
>> > @@ -1508,6 +1508,28 @@ record_store (rtx body, bb_info_t bb_info)
>> >
>> > if (tem && CONSTANT_P (tem))
>> > const_rhs = tem;
>> > + else
>> > + {
>> > + /* If RHS is set only once to a constant, set CONST_RHS
>> > + to the constant. */
>> > + df_ref def = DF_REG_DEF_CHAIN (REGNO (rhs));
>> > + if (def != nullptr
>> > + && !DF_REF_IS_ARTIFICIAL (def)
>> > + && !(DF_REF_FLAGS (def)
>> > + & (DF_REF_PARTIAL | DF_REF_CONDITIONAL))
>> > + && !DF_REF_NEXT_REG (def))
>>
>> Can we introduce a helper for this? There are already similar tests
>> in ira and loop-iv, and it seems a bit too complex to have to open-code
>> each time.
>
> I can use find_single_def_src in loop-iv.cc:
>
> /* If REGNO has a single definition, return its known value, otherwise return
> null. */
>
> rtx
> find_single_def_src (unsigned int regno)
Yeah, reusing that sounds good. Perhaps we should move it into df-core.cc,
alongside the df_reg_used group of functions.
I think the mode check in your original patch should be kept though,
so how about we change the parameter to an rtx reg and use rtx_equal in:
rtx set = single_set (DF_REF_INSN (adef));
if (set == NULL || !REG_P (SET_DEST (set))
|| REGNO (SET_DEST (set)) != regno)
return NULL_RTX;
rather than the existing !REG_P and REGNO checks. We should also add:
>
> and do
>
> /* If RHS is set only once to a constant, set CONST_RHS
> to the constant. */
> rtx def_src = find_single_def_src (REGNO (rhs));
> if (def_src != nullptr && CONSTANT_P (def_src))
> {
> df_ref def = DF_REG_DEF_CHAIN (REGNO (rhs));
> if (!(DF_REF_FLAGS (def)
> & (DF_REF_PARTIAL | DF_REF_CONDITIONAL)))
…this check to the function, since it's needed for correctness even
in the loop-iv.cc use.
Thanks,
Richard
> {
> rtx_insn *def_insn = DF_REF_INSN (def);
> rtx def_body = single_set (def_insn);
> if (rhs == SET_DEST (def_body))
> const_rhs = def_src;
> }
> }
> }
>
> Will it work?
>
> Thanks.
>
>> Thanks,
>> Richard
>>
>> > + {
>> > + rtx_insn *def_insn = DF_REF_INSN (def);
>> > + rtx def_body = PATTERN (def_insn);
>> > + if (GET_CODE (def_body) == SET)
>> > + {
>> > + rtx def_src = SET_SRC (def_body);
>> > + if (CONSTANT_P (def_src)
>> > + && GET_MODE (def_src) == GET_MODE (rhs))
>> > + const_rhs = def_src;
>> > + }
>> > + }
>> > + }
>> > }
>> > }
>> >
>> > diff --git a/gcc/testsuite/g++.target/i386/pr105638.C
>> > b/gcc/testsuite/g++.target/i386/pr105638.C
>> > new file mode 100644
>> > index 00000000000..ff40a459de1
>> > --- /dev/null
>> > +++ b/gcc/testsuite/g++.target/i386/pr105638.C
>> > @@ -0,0 +1,44 @@
>> > +/* { dg-do compile { target { ! ia32 } } } */
>> > +/* { dg-options "-std=gnu++20 -O2 -march=skylake" } */
>> > +/* { dg-final { scan-assembler-not "vpxor" } } */
>> > +
>> > +#include <stdint.h>
>> > +#include <vector>
>> > +#include <tr1/array>
>> > +
>> > +class FastBoard {
>> > +public:
>> > + typedef std::pair<int, int> movescore_t;
>> > + typedef std::tr1::array<movescore_t, 24> scoredlist_t;
>> > +
>> > +protected:
>> > + std::vector<int> m_critical;
>> > +
>> > + int m_boardsize;
>> > +};
>> > +
>> > +class FastState {
>> > +public:
>> > + FastBoard board;
>> > +
>> > + int movenum;
>> > +protected:
>> > + FastBoard::scoredlist_t scoredmoves;
>> > +};
>> > +
>> > +class KoState : public FastState {
>> > +private:
>> > + std::vector<uint64_t> ko_hash_history;
>> > + std::vector<uint64_t> hash_history;
>> > +};
>> > +
>> > +class GameState : public KoState {
>> > +public:
>> > + void foo ();
>> > +private:
>> > + std::vector<KoState> game_history;
>> > +};
>> > +
>> > +void GameState::foo() {
>> > + game_history.resize(movenum);
>> > +}
