Match: Simplify (x != 0 ? x + ~0 : 0) to (x - x != 0).

When the imm operand op1=1 in the unsigned scalar sat_sub form2 below,
we can simplify (x != 0 ? x + ~0 : 0) to (x - x != 0), thereby eliminating
a branch instruction.This simplification also applies to signed integer.

Form2:
T __attribute__((noinline))             \
sat_u_sub_imm##IMM##_##T##_fmt_2 (T x)  \
{                                       \
  return x >= (T)IMM ? x - (T)IMM : 0;  \
}

Take below form 2 as example:
DEF_SAT_U_SUB_IMM_FMT_2(uint8_t, 1)

Before this patch:
__attribute__((noinline))
uint8_t sat_u_sub_imm1_uint8_t_fmt_2 (uint8_t x)
{
  uint8_t _1;
  uint8_t _3;

  <bb 2> [local count: 1073741824]:
  if (x_2(D) != 0)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> [local count: 536870912]:
  _3 = x_2(D) + 255;

  <bb 4> [local count: 1073741824]:
  # _1 = PHI <x_2(D)(2), _3(3)>
  return _1;

}

Assembly code:
sat_u_sub_imm1_uint8_t_fmt_2:
	beq	a0,zero,.L2
	addiw	a0,a0,-1
	andi	a0,a0,0xff
.L2:
	ret

After this patch:
__attribute__((noinline))
uint8_t sat_u_sub_imm1_uint8_t_fmt_2 (uint8_t x)
{
  _Bool _1;
  unsigned char _2;
  uint8_t _4;

  <bb 2> [local count: 1073741824]:
  _1 = x_3(D) != 0;
  _2 = (unsigned char) _1;
  _4 = x_3(D) - _2;
  return _4;

}

Assembly code:
sat_u_sub_imm1_uint8_t_fmt_2:
	snez	a5,a0
	subw	a0,a0,a5
	andi	a0,a0,0xff
	ret

The below test suites are passed for this patch:
1. The rv64gcv fully regression tests.
2. The x86 bootstrap tests.
3. The x86 fully regression tests.

Signed-off-by: Li Xu <xuli1@eswincomputing.com>

gcc/ChangeLog:

	* match.pd: Simplify (x != 0 ? x + ~0 : 0) to (x - x != 0).

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/phi-opt-44.c: New test.
	* gcc.dg/tree-ssa/phi-opt-45.c: New test.

0 files changed, 0 insertions, 0 deletions