Match: Support IMM=max-1 for unsigned scalar .SAT_SUB IMM form 1

This patch would like to support .SAT_SUB when one of the op
is IMM = max - 1 of form1.

Form 1:
 #define DEF_SAT_U_SUB_IMM_FMT_1(T, IMM) \
 T __attribute__((noinline))             \
 sat_u_sub_imm##IMM##_##T##_fmt_1 (T y)  \
 {                                       \
   return IMM >= y ? IMM - y : 0;        \
 }

Take below form 1 as example:
DEF_SAT_U_SUB_IMM_FMT_1(uint8_t, 254)

Before this patch:
__attribute__((noinline))
uint8_t sat_u_sub_imm254_uint8_t_fmt_1 (uint8_t y)
{
  uint8_t _1;
  uint8_t _3;

  <bb 2> [local count: 1073741824]:
  if (y_2(D) != 255)
    goto <bb 3>; [66.00%]
  else
    goto <bb 4>; [34.00%]

  <bb 3> [local count: 708669600]:
  _3 = 254 - y_2(D);

  <bb 4> [local count: 1073741824]:
  # _1 = PHI <0(2), _3(3)>
  return _1;

}

After this patch:
__attribute__((noinline))
uint8_t sat_u_sub_imm254_uint8_t_fmt_1 (uint8_t y)
{
  uint8_t _1;

  <bb 2> [local count: 1073741824]:
  _1 = .SAT_SUB (254, y_2(D)); [tail call]
  return _1;

}

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: Support IMM=max-1.

1 files changed, 17 insertions, 1 deletions

diff --git a/gcc/match.pd b/gcc/match.pd
index ec2038d..362bcac 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3325,7 +3325,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
       && types_match (type, @0, @1))))
 
-/* Unsigned saturation sub with op_0 imm, case 9 (branch with gt):
+/* Unsigned saturation sub with op_0 imm, case 9 (branch with le):
    SAT_U_SUB = IMM > Y  ? (IMM - Y) : 0.
              = IMM >= Y ? (IMM - Y) : 0.  */
 (match (unsigned_integer_sat_sub @0 @1)
@@ -3344,6 +3344,22 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   }
   (if (equal_p || less_than_1_p)))))
 
+/* The boundary condition for case 9: IMM = max -1  (branch with ne):
+   SAT_U_SUB = IMM >= Y ? (IMM - Y) : 0.  */
+(match (unsigned_integer_sat_sub @0 @1)
+ (cond^ (ne @1 INTEGER_CST@2) (minus INTEGER_CST@0 @1) integer_zerop)
+ (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
+     && types_match (type, @1))
+(with
+  {
+   unsigned precision = TYPE_PRECISION (type);
+   wide_int max = wi::mask (precision, false, precision);
+   wide_int c0 = wi::to_wide (@0);
+   wide_int c2 = wi::to_wide (@2);
+   wide_int c0_add_1 = wi::add (c0, wi::uhwi (1, precision));
+  }
+  (if (wi::eq_p (c2, max) && wi::eq_p (c0_add_1, max))))))
+
 /* Unsigned saturation sub with op_1 imm, case 10:
    SAT_U_SUB = X > IMM  ? (X - IMM) : 0.
              = X >= IMM ? (X - IMM) : 0.  */