Re: [PATCH] x86: Add cmpmemsi for -mgeneral-regs-only

[Uros Bizjak <ubizjak@gmail.com>]

On Sun, May 17, 2020 at 7:06 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> Duplicate the cmpstrn pattern for cmpmem.  The only difference is that
> the length argument of cmpmem is guaranteed to be less than or equal to
> lengths of 2 memory areas.  Since "repz cmpsb" can be much slower than
> memcmp function implemented with vector instruction, see
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43052
>
> expand cmpmem to "repz cmpsb" only with -mgeneral-regs-only.

If there is no benefit compared to the library implementation, then
enable these patterns only when -minline-all-stringops is used.

Eventually these should be reimplemented with SSE4 string instructions.

Honza is the author of the block handling x86 system, I'll leave the
review to him.

Uros.

> Tested on Linux/x86 and Linux/x86-64.  OK for master?
>
> Thanks.
>
> H.J.
> ---
> gcc/
>
>         PR target/95151
>         * config/i386/i386-expand.c (ix86_expand_cmpstrn_or_cmpmem): New
>         function.  Duplicated from the cmpstrn pattern.  Expand memcmp
>         to "repz cmpsb" only with -mgeneral-regs-only.
>         * config/i386/i386-protos.h (ix86_expand_cmpstrn_or_cmpmem): New
>         prototype.
>         * config/i386/i386.md (cmpmemsi): New pattern.
>         (cmpstrnsi): Use ix86_expand_cmpstrn_or_cmpmem.
>
> gcc/testsuite/
>
>         PR target/95151
>         * gcc.target/i386/pr95151-1.c: New test.
>         * gcc.target/i386/pr95151-2.c: Likewise.
>         * gcc.target/i386/pr95151-3.c: Likewise.
>         * gcc.target/i386/pr95151-4.c: Likewise.
> ---
>  gcc/config/i386/i386-expand.c             | 80 +++++++++++++++++++++++
>  gcc/config/i386/i386-protos.h             |  1 +
>  gcc/config/i386/i386.md                   | 80 ++++++-----------------
>  gcc/testsuite/gcc.target/i386/pr95151-1.c | 18 +++++
>  gcc/testsuite/gcc.target/i386/pr95151-2.c | 11 ++++
>  gcc/testsuite/gcc.target/i386/pr95151-3.c | 18 +++++
>  gcc/testsuite/gcc.target/i386/pr95151-4.c | 11 ++++
>  7 files changed, 160 insertions(+), 59 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr95151-1.c
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr95151-2.c
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr95151-3.c
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr95151-4.c
>
> diff --git a/gcc/config/i386/i386-expand.c b/gcc/config/i386/i386-expand.c
> index 26531585c5f..05d3c33720c 100644
> --- a/gcc/config/i386/i386-expand.c
> +++ b/gcc/config/i386/i386-expand.c
> @@ -7651,6 +7651,86 @@ ix86_expand_set_or_cpymem (rtx dst, rtx src, rtx count_exp, rtx val_exp,
>    return true;
>  }
>
> +/* Expand cmpstrn or memcmp.  */
> +
> +bool
> +ix86_expand_cmpstrn_or_cmpmem (rtx result, rtx src1, rtx src2,
> +                              rtx length, rtx align, bool is_cmpstrn)
> +{
> +  if (optimize_insn_for_size_p () && !TARGET_INLINE_ALL_STRINGOPS)
> +    return false;
> +
> +  /* Can't use this if the user has appropriated ecx, esi or edi.  */
> +  if (fixed_regs[CX_REG] || fixed_regs[SI_REG] || fixed_regs[DI_REG])
> +    return false;
> +
> +  if (is_cmpstrn)
> +    {
> +      /* For strncmp, length is the maximum length, which can be larger
> +        than actual string lengths.  We can expand the cmpstrn pattern
> +        to "repz cmpsb" only if one of the strings is a constant so
> +        that expand_builtin_strncmp() can write the length argument to
> +        be the minimum of the const string length and the actual length
> +        argument.  Otherwise, "repz cmpsb" may pass the 0 byte.  */
> +      tree t1 = MEM_EXPR (src1);
> +      tree t2 = MEM_EXPR (src2);
> +      if (!((t1 && TREE_CODE (t1) == MEM_REF
> +            && TREE_CODE (TREE_OPERAND (t1, 0)) == ADDR_EXPR
> +            && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (t1, 0), 0))
> +                == STRING_CST))
> +           || (t2 && TREE_CODE (t2) == MEM_REF
> +               && TREE_CODE (TREE_OPERAND (t2, 0)) == ADDR_EXPR
> +               && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (t2, 0), 0))
> +                   == STRING_CST))))
> +       return false;
> +    }
> +  else
> +    {
> +      /* Expand memcmp to "repz cmpsb" only for -mgeneral-regs-only
> +        since "repz cmpsb" can be much slower than memcmp function
> +        implemented with vector instructions, see
> +
> +        https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43052
> +       */
> +      if (!TARGET_GENERAL_REGS_ONLY)
> +       return false;
> +    }
> +
> +  rtx addr1 = copy_addr_to_reg (XEXP (src1, 0));
> +  rtx addr2 = copy_addr_to_reg (XEXP (src2, 0));
> +  if (addr1 != XEXP (src1, 0))
> +    src1 = replace_equiv_address_nv (src1, addr1);
> +  if (addr2 != XEXP (src2, 0))
> +    src2 = replace_equiv_address_nv (src2, addr2);
> +
> +  rtx lengthreg = ix86_zero_extend_to_Pmode (length);
> +
> +  /* If we are testing strict equality, we can use known alignment to
> +     good advantage.  This may be possible with combine, particularly
> +     once cc0 is dead.  */
> +  if (CONST_INT_P (length))
> +    {
> +      if (length == const0_rtx)
> +       {
> +         emit_move_insn (result, const0_rtx);
> +         return true;
> +       }
> +      emit_insn (gen_cmpstrnqi_nz_1 (addr1, addr2, lengthreg, align,
> +                                    src1, src2));
> +    }
> +  else
> +    {
> +      emit_insn (gen_cmp_1 (Pmode, lengthreg, lengthreg));
> +      emit_insn (gen_cmpstrnqi_1 (addr1, addr2, lengthreg, align,
> +                                 src1, src2));
> +    }
> +
> +  rtx out = gen_lowpart (QImode, result);
> +  emit_insn (gen_cmpintqi (out));
> +  emit_move_insn (result, gen_rtx_SIGN_EXTEND (SImode, out));
> +
> +  return true;
> +}
>
>  /* Expand the appropriate insns for doing strlen if not just doing
>     repnz; scasb
> diff --git a/gcc/config/i386/i386-protos.h b/gcc/config/i386/i386-protos.h
> index 39fcaa0ad5f..238aa650b61 100644
> --- a/gcc/config/i386/i386-protos.h
> +++ b/gcc/config/i386/i386-protos.h
> @@ -71,6 +71,7 @@ extern int avx_vperm2f128_parallel (rtx par, machine_mode mode);
>  extern bool ix86_expand_strlen (rtx, rtx, rtx, rtx);
>  extern bool ix86_expand_set_or_cpymem (rtx, rtx, rtx, rtx, rtx, rtx,
>                                        rtx, rtx, rtx, rtx, bool);
> +extern bool ix86_expand_cmpstrn_or_cmpmem (rtx, rtx, rtx, rtx, rtx, bool);
>
>  extern bool constant_address_p (rtx);
>  extern bool legitimate_pic_operand_p (rtx);
> diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
> index 1bf0c1a7f01..7fb97db1e6e 100644
> --- a/gcc/config/i386/i386.md
> +++ b/gcc/config/i386/i386.md
> @@ -17761,6 +17761,22 @@ (define_insn "*rep_stosqi"
>           (const_string "*")))
>     (set_attr "mode" "QI")])
>
> +(define_expand "cmpmemsi"
> +  [(set (match_operand:SI 0 "register_operand" "")
> +        (compare:SI (match_operand:BLK 1 "memory_operand" "")
> +                    (match_operand:BLK 2 "memory_operand" "") ) )
> +   (use (match_operand 3 "general_operand"))
> +   (use (match_operand 4 "immediate_operand"))]
> +  ""
> +{
> +  if (ix86_expand_cmpstrn_or_cmpmem (operands[0], operands[1],
> +                                    operands[2], operands[3],
> +                                    operands[4], false))
> +    DONE;
> +  else
> +    FAIL;
> +})
> +
>  (define_expand "cmpstrnsi"
>    [(set (match_operand:SI 0 "register_operand")
>         (compare:SI (match_operand:BLK 1 "general_operand")
> @@ -17769,66 +17785,12 @@ (define_expand "cmpstrnsi"
>     (use (match_operand 4 "immediate_operand"))]
>    ""
>  {
> -  rtx addr1, addr2, countreg, align, out;
> -
> -  if (optimize_insn_for_size_p () && !TARGET_INLINE_ALL_STRINGOPS)
> -    FAIL;
> -
> -  /* Can't use this if the user has appropriated ecx, esi or edi.  */
> -  if (fixed_regs[CX_REG] || fixed_regs[SI_REG] || fixed_regs[DI_REG])
> -    FAIL;
> -
> -  /* One of the strings must be a constant.  If so, expand_builtin_strncmp()
> -     will have rewritten the length arg to be the minimum of the const string
> -     length and the actual length arg.  If both strings are the same and
> -     shorter than the length arg, repz cmpsb will not stop at the 0 byte and
> -     will incorrectly base the results on chars past the 0 byte.  */
> -  tree t1 = MEM_EXPR (operands[1]);
> -  tree t2 = MEM_EXPR (operands[2]);
> -  if (!((t1 && TREE_CODE (t1) == MEM_REF
> -         && TREE_CODE (TREE_OPERAND (t1, 0)) == ADDR_EXPR
> -         && TREE_CODE (TREE_OPERAND (TREE_OPERAND (t1, 0), 0)) == STRING_CST)
> -      || (t2 && TREE_CODE (t2) == MEM_REF
> -          && TREE_CODE (TREE_OPERAND (t2, 0)) == ADDR_EXPR
> -          && TREE_CODE (TREE_OPERAND (TREE_OPERAND (t2, 0), 0)) == STRING_CST)))
> -    FAIL;
> -
> -  addr1 = copy_addr_to_reg (XEXP (operands[1], 0));
> -  addr2 = copy_addr_to_reg (XEXP (operands[2], 0));
> -  if (addr1 != XEXP (operands[1], 0))
> -    operands[1] = replace_equiv_address_nv (operands[1], addr1);
> -  if (addr2 != XEXP (operands[2], 0))
> -    operands[2] = replace_equiv_address_nv (operands[2], addr2);
> -
> -  countreg = ix86_zero_extend_to_Pmode (operands[3]);
> -
> -  /* %%% Iff we are testing strict equality, we can use known alignment
> -     to good advantage.  This may be possible with combine, particularly
> -     once cc0 is dead.  */
> -  align = operands[4];
> -
> -  if (CONST_INT_P (operands[3]))
> -    {
> -      if (operands[3] == const0_rtx)
> -       {
> -         emit_move_insn (operands[0], const0_rtx);
> -         DONE;
> -       }
> -      emit_insn (gen_cmpstrnqi_nz_1 (addr1, addr2, countreg, align,
> -                                    operands[1], operands[2]));
> -    }
> +  if (ix86_expand_cmpstrn_or_cmpmem (operands[0], operands[1],
> +                                    operands[2], operands[3],
> +                                    operands[4], true))
> +    DONE;
>    else
> -    {
> -      emit_insn (gen_cmp_1 (Pmode, countreg, countreg));
> -      emit_insn (gen_cmpstrnqi_1 (addr1, addr2, countreg, align,
> -                                 operands[1], operands[2]));
> -    }
> -
> -  out = gen_lowpart (QImode, operands[0]);
> -  emit_insn (gen_cmpintqi (out));
> -  emit_move_insn (operands[0], gen_rtx_SIGN_EXTEND (SImode, out));
> -
> -  DONE;
> +    FAIL;
>  })
>
>  ;; Produce a tri-state integer (-1, 0, 1) from condition codes.
> diff --git a/gcc/testsuite/gcc.target/i386/pr95151-1.c b/gcc/testsuite/gcc.target/i386/pr95151-1.c
> new file mode 100644
> index 00000000000..f7ed88e508f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr95151-1.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mgeneral-regs-only -minline-all-stringops" } */
> +
> +struct foo
> +{
> +  char array[257];
> +};
> +
> +extern struct foo x;
> +
> +int
> +func (struct foo i)
> +{
> +  return __builtin_memcmp (&x, &i, sizeof (x)) ? 1 : 2;
> +}
> +
> +/* { dg-final { scan-assembler-not "call\[\\t \]*_?memcmp" } } */
> +/* { dg-final { scan-assembler "repz cmpsb" } } */
> diff --git a/gcc/testsuite/gcc.target/i386/pr95151-2.c b/gcc/testsuite/gcc.target/i386/pr95151-2.c
> new file mode 100644
> index 00000000000..afd811ae7fb
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr95151-2.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mgeneral-regs-only -minline-all-stringops" } */
> +
> +int
> +func (void *d, void *s, unsigned int l)
> +{
> +  return __builtin_memcmp (d, s, l) ? 1 : 2;
> +}
> +
> +/* { dg-final { scan-assembler-not "call\[\\t \]*_?memcmp" } } */
> +/* { dg-final { scan-assembler "repz cmpsb" } } */
> diff --git a/gcc/testsuite/gcc.target/i386/pr95151-3.c b/gcc/testsuite/gcc.target/i386/pr95151-3.c
> new file mode 100644
> index 00000000000..bd62db5e640
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr95151-3.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -msse2 -minline-all-stringops" } */
> +
> +struct foo
> +{
> +  char array[257];
> +};
> +
> +extern struct foo x;
> +
> +int
> +func (struct foo i)
> +{
> +  return __builtin_memcmp (&x, &i, sizeof (x)) ? 1 : 2;
> +}
> +
> +/* { dg-final { scan-assembler "call\[\\t \]*_?memcmp" } } */
> +/* { dg-final { scan-assembler-not "repz cmpsb" } } */
> diff --git a/gcc/testsuite/gcc.target/i386/pr95151-4.c b/gcc/testsuite/gcc.target/i386/pr95151-4.c
> new file mode 100644
> index 00000000000..b8258f2530a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr95151-4.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -msse2 -minline-all-stringops" } */
> +
> +int
> +func (void *d, void *s, unsigned int l)
> +{
> +  return __builtin_memcmp (d, s, l) ? 1 : 2;
> +}
> +
> +/* { dg-final { scan-assembler "call\[\\t \]*_?memcmp" } } */
> +/* { dg-final { scan-assembler-not "repz cmpsb" } } */
> --
> 2.26.2
>