"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.
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);
> +}
