Re: [PATCH v2] combine: Narrow comparison of memory and constant

[Stefan Schulze Frielinghaus <stefansf@linux.ibm.com>]

ping

On Mon, Jun 19, 2023 at 04:23:57PM +0200, Stefan Schulze Frielinghaus wrote:
> Comparisons between memory and constants might be done in a smaller mode
> resulting in smaller constants which might finally end up as immediates
> instead of in the literal pool.
> 
> For example, on s390x a non-symmetric comparison like
>   x <= 0x3fffffffffffffff
> results in the constant being spilled to the literal pool and an 8 byte
> memory comparison is emitted.  Ideally, an equivalent comparison
>   x0 <= 0x3f
> where x0 is the most significant byte of x, is emitted where the
> constant is smaller and more likely to materialize as an immediate.
> 
> Similarly, comparisons of the form
>   x >= 0x4000000000000000
> can be shortened into x0 >= 0x40.
> 
> Bootstrapped and regtested on s390x, x64, aarch64, and powerpc64le.
> Note, the new tests show that for the mentioned little-endian targets
> the optimization does not materialize since either the costs of the new
> instructions are higher or they do not match.  Still ok for mainline?
> 
> gcc/ChangeLog:
> 
> 	* combine.cc (simplify_compare_const): Narrow comparison of
> 	memory and constant.
> 	(try_combine): Adapt new function signature.
> 	(simplify_comparison): Adapt new function signature.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.dg/cmp-mem-const-1.c: New test.
> 	* gcc.dg/cmp-mem-const-2.c: New test.
> 	* gcc.dg/cmp-mem-const-3.c: New test.
> 	* gcc.dg/cmp-mem-const-4.c: New test.
> 	* gcc.dg/cmp-mem-const-5.c: New test.
> 	* gcc.dg/cmp-mem-const-6.c: New test.
> 	* gcc.target/s390/cmp-mem-const-1.c: New test.
> ---
>  gcc/combine.cc                                | 79 +++++++++++++++++--
>  gcc/testsuite/gcc.dg/cmp-mem-const-1.c        | 17 ++++
>  gcc/testsuite/gcc.dg/cmp-mem-const-2.c        | 17 ++++
>  gcc/testsuite/gcc.dg/cmp-mem-const-3.c        | 17 ++++
>  gcc/testsuite/gcc.dg/cmp-mem-const-4.c        | 17 ++++
>  gcc/testsuite/gcc.dg/cmp-mem-const-5.c        | 17 ++++
>  gcc/testsuite/gcc.dg/cmp-mem-const-6.c        | 17 ++++
>  .../gcc.target/s390/cmp-mem-const-1.c         | 24 ++++++
>  8 files changed, 200 insertions(+), 5 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/cmp-mem-const-1.c
>  create mode 100644 gcc/testsuite/gcc.dg/cmp-mem-const-2.c
>  create mode 100644 gcc/testsuite/gcc.dg/cmp-mem-const-3.c
>  create mode 100644 gcc/testsuite/gcc.dg/cmp-mem-const-4.c
>  create mode 100644 gcc/testsuite/gcc.dg/cmp-mem-const-5.c
>  create mode 100644 gcc/testsuite/gcc.dg/cmp-mem-const-6.c
>  create mode 100644 gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
> 
> diff --git a/gcc/combine.cc b/gcc/combine.cc
> index 5aa0ec5c45a..56e15a93409 100644
> --- a/gcc/combine.cc
> +++ b/gcc/combine.cc
> @@ -460,7 +460,7 @@ static rtx simplify_shift_const (rtx, enum rtx_code, machine_mode, rtx,
>  static int recog_for_combine (rtx *, rtx_insn *, rtx *);
>  static rtx gen_lowpart_for_combine (machine_mode, rtx);
>  static enum rtx_code simplify_compare_const (enum rtx_code, machine_mode,
> -					     rtx, rtx *);
> +					     rtx *, rtx *);
>  static enum rtx_code simplify_comparison (enum rtx_code, rtx *, rtx *);
>  static void update_table_tick (rtx);
>  static void record_value_for_reg (rtx, rtx_insn *, rtx);
> @@ -3185,7 +3185,7 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
>  	  compare_code = orig_compare_code = GET_CODE (*cc_use_loc);
>  	  if (is_a <scalar_int_mode> (GET_MODE (i2dest), &mode))
>  	    compare_code = simplify_compare_const (compare_code, mode,
> -						   op0, &op1);
> +						   &op0, &op1);
>  	  target_canonicalize_comparison (&compare_code, &op0, &op1, 1);
>  	}
>  
> @@ -11796,13 +11796,14 @@ gen_lowpart_for_combine (machine_mode omode, rtx x)
>     (CODE OP0 const0_rtx) form.
>  
>     The result is a possibly different comparison code to use.
> -   *POP1 may be updated.  */
> +   *POP0 and *POP1 may be updated.  */
>  
>  static enum rtx_code
>  simplify_compare_const (enum rtx_code code, machine_mode mode,
> -			rtx op0, rtx *pop1)
> +			rtx *pop0, rtx *pop1)
>  {
>    scalar_int_mode int_mode;
> +  rtx op0 = *pop0;
>    HOST_WIDE_INT const_op = INTVAL (*pop1);
>  
>    /* Get the constant we are comparing against and turn off all bits
> @@ -11987,6 +11988,74 @@ simplify_compare_const (enum rtx_code code, machine_mode mode,
>        break;
>      }
>  
> +  /* Narrow non-symmetric comparison of memory and constant as e.g.
> +     x0...x7 <= 0x3fffffffffffffff into x0 <= 0x3f where x0 is the most
> +     significant byte.  Likewise, transform x0...x7 >= 0x4000000000000000 into
> +     x0 >= 0x40.  */
> +  if ((code == LEU || code == LTU || code == GEU || code == GTU)
> +      && is_a <scalar_int_mode> (GET_MODE (op0), &int_mode)
> +      && MEM_P (op0)
> +      && !MEM_VOLATILE_P (op0)
> +      /* The optimization makes only sense for constants which are big enough
> +	 so that we have a chance to chop off something at all.  */
> +      && (unsigned HOST_WIDE_INT) const_op > 0xff
> +      /* Ensure that we do not overflow during normalization.  */
> +      && (code != GTU || (unsigned HOST_WIDE_INT) const_op < HOST_WIDE_INT_M1U))
> +    {
> +      unsigned HOST_WIDE_INT n = (unsigned HOST_WIDE_INT) const_op;
> +      enum rtx_code adjusted_code;
> +
> +      /* Normalize code to either LEU or GEU.  */
> +      if (code == LTU)
> +	{
> +	  --n;
> +	  adjusted_code = LEU;
> +	}
> +      else if (code == GTU)
> +	{
> +	  ++n;
> +	  adjusted_code = GEU;
> +	}
> +      else
> +	adjusted_code = code;
> +
> +      scalar_int_mode narrow_mode_iter;
> +      FOR_EACH_MODE_UNTIL (narrow_mode_iter, int_mode)
> +	{
> +	  unsigned nbits = GET_MODE_PRECISION (int_mode)
> +			   - GET_MODE_PRECISION (narrow_mode_iter);
> +	  unsigned HOST_WIDE_INT mask = (HOST_WIDE_INT_1U << nbits) - 1;
> +	  unsigned HOST_WIDE_INT lower_bits = n & mask;
> +	  if ((adjusted_code == LEU && lower_bits == mask)
> +	      || (adjusted_code == GEU && lower_bits == 0))
> +	    {
> +	      n >>= nbits;
> +	      break;
> +	    }
> +	}
> +
> +      if (narrow_mode_iter < int_mode)
> +	{
> +	  if (dump_file && (dump_flags & TDF_DETAILS))
> +	    {
> +	      fprintf (
> +		dump_file, "narrow comparison from mode %s to %s: (MEM %s "
> +		HOST_WIDE_INT_PRINT_HEX ") to (MEM %s "
> +		HOST_WIDE_INT_PRINT_HEX ").\n", GET_MODE_NAME (int_mode),
> +		GET_MODE_NAME (narrow_mode_iter), GET_RTX_NAME (code),
> +		(unsigned HOST_WIDE_INT)const_op, GET_RTX_NAME (adjusted_code),
> +		n);
> +	    }
> +	  poly_int64 offset = (BYTES_BIG_ENDIAN
> +			       ? 0
> +			       : (GET_MODE_SIZE (int_mode)
> +				  - GET_MODE_SIZE (narrow_mode_iter)));
> +	  *pop0 = adjust_address_nv (op0, narrow_mode_iter, offset);
> +	  *pop1 = GEN_INT (n);
> +	  return adjusted_code;
> +	}
> +    }
> +
>    *pop1 = GEN_INT (const_op);
>    return code;
>  }
> @@ -12179,7 +12248,7 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
>  
>        /* Try to simplify the compare to constant, possibly changing the
>  	 comparison op, and/or changing op1 to zero.  */
> -      code = simplify_compare_const (code, raw_mode, op0, &op1);
> +      code = simplify_compare_const (code, raw_mode, &op0, &op1);
>        const_op = INTVAL (op1);
>  
>        /* Compute some predicates to simplify code below.  */
> diff --git a/gcc/testsuite/gcc.dg/cmp-mem-const-1.c b/gcc/testsuite/gcc.dg/cmp-mem-const-1.c
> new file mode 100644
> index 00000000000..263ad98af79
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/cmp-mem-const-1.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile { target { lp64 } } } */
> +/* { dg-options "-O1 -fdump-rtl-combine-details" } */
> +/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to QI" "combine" } } */
> +
> +typedef __UINT64_TYPE__ uint64_t;
> +
> +int
> +le_1byte_a (uint64_t *x)
> +{
> +  return *x <= 0x3fffffffffffffff;
> +}
> +
> +int
> +le_1byte_b (uint64_t *x)
> +{
> +  return *x < 0x4000000000000000;
> +}
> diff --git a/gcc/testsuite/gcc.dg/cmp-mem-const-2.c b/gcc/testsuite/gcc.dg/cmp-mem-const-2.c
> new file mode 100644
> index 00000000000..a7cc5348295
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/cmp-mem-const-2.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile { target { lp64 } } } */
> +/* { dg-options "-O1 -fdump-rtl-combine-details" } */
> +/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to QI" "combine" } } */
> +
> +typedef __UINT64_TYPE__ uint64_t;
> +
> +int
> +ge_1byte_a (uint64_t *x)
> +{
> +  return *x > 0x3fffffffffffffff;
> +}
> +
> +int
> +ge_1byte_b (uint64_t *x)
> +{
> +  return *x >= 0x4000000000000000;
> +}
> diff --git a/gcc/testsuite/gcc.dg/cmp-mem-const-3.c b/gcc/testsuite/gcc.dg/cmp-mem-const-3.c
> new file mode 100644
> index 00000000000..06f80bf72d8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/cmp-mem-const-3.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile { target { lp64 } } } */
> +/* { dg-options "-O1 -fdump-rtl-combine-details" } */
> +/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to HI" "combine" } } */
> +
> +typedef __UINT64_TYPE__ uint64_t;
> +
> +int
> +le_2bytes_a (uint64_t *x)
> +{
> +  return *x <= 0x3ffdffffffffffff;
> +}
> +
> +int
> +le_2bytes_b (uint64_t *x)
> +{
> +  return *x < 0x3ffe000000000000;
> +}
> diff --git a/gcc/testsuite/gcc.dg/cmp-mem-const-4.c b/gcc/testsuite/gcc.dg/cmp-mem-const-4.c
> new file mode 100644
> index 00000000000..407999abf7e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/cmp-mem-const-4.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile { target { lp64 } } } */
> +/* { dg-options "-O1 -fdump-rtl-combine-details" } */
> +/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to HI" "combine" } } */
> +
> +typedef __UINT64_TYPE__ uint64_t;
> +
> +int
> +ge_2bytes_a (uint64_t *x)
> +{
> +  return *x > 0x400cffffffffffff;
> +}
> +
> +int
> +ge_2bytes_b (uint64_t *x)
> +{
> +  return *x >= 0x400d000000000000;
> +}
> diff --git a/gcc/testsuite/gcc.dg/cmp-mem-const-5.c b/gcc/testsuite/gcc.dg/cmp-mem-const-5.c
> new file mode 100644
> index 00000000000..e16773f5bcf
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/cmp-mem-const-5.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile { target { lp64 } } } */
> +/* { dg-options "-O1 -fdump-rtl-combine-details" } */
> +/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to SI" "combine" } } */
> +
> +typedef __UINT64_TYPE__ uint64_t;
> +
> +int
> +le_4bytes_a (uint64_t *x)
> +{
> +  return *x <= 0x3ffffdffffffffff;
> +}
> +
> +int
> +le_4bytes_b (uint64_t *x)
> +{
> +  return *x < 0x3ffffe0000000000;
> +}
> diff --git a/gcc/testsuite/gcc.dg/cmp-mem-const-6.c b/gcc/testsuite/gcc.dg/cmp-mem-const-6.c
> new file mode 100644
> index 00000000000..8f53b5678bd
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/cmp-mem-const-6.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile { target { lp64 } } } */
> +/* { dg-options "-O1 -fdump-rtl-combine-details" } */
> +/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to SI" "combine" } } */
> +
> +typedef __UINT64_TYPE__ uint64_t;
> +
> +int
> +ge_4bytes_a (uint64_t *x)
> +{
> +  return *x > 0x4000cfffffffffff;
> +}
> +
> +int
> +ge_4bytes_b (uint64_t *x)
> +{
> +  return *x >= 0x4000d00000000000;
> +}
> diff --git a/gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c b/gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
> new file mode 100644
> index 00000000000..309aafbec01
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/s390/cmp-mem-const-1.c
> @@ -0,0 +1,24 @@
> +/* { dg-do compile { target { lp64 } } } */
> +/* { dg-options "-O1 -march=z13 -mzarch -fdump-rtl-combine-details" } */
> +/* { dg-final { scan-assembler-not {\tclc\t} } } */
> +/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to QI" "combine" } } */
> +
> +struct s
> +{
> +  long a;
> +  unsigned b : 1;
> +  unsigned c : 1;
> +};
> +
> +int foo (struct s *x)
> +{
> +  /* Expression
> +       x->b || x->c
> +     is transformed into
> +       _1 = BIT_FIELD_REF <*x_4(D), 64, 64>;
> +       _2 = _1 > 0x3FFFFFFFFFFFFFFF;
> +     where the constant may materialize in the literal pool and an 8 byte CLC
> +     may be emitted.  Ensure this is not the case.
> +  */
> +  return x->b || x->c;
> +}
> -- 
> 2.39.2
>