[gcc r15-4534] Match: Support IMM=max-1 for unsigned scalar .SAT_SUB IMM form 1

[Li Xu via Gcc-cvs]

https://gcc.gnu.org/g:1dccec47ab679926521fd4c9963b63b319b56eb9

commit r15-4534-g1dccec47ab679926521fd4c9963b63b319b56eb9
Author: xuli <xu...@eswincomputing.com>
Date:   Tue Oct 22 01:08:56 2024 +0000

    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 <xu...@eswincomputing.com>
    
    gcc/ChangeLog:
    
            * match.pd: Support IMM=max-1.

Diff:
---
 gcc/match.pd | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/gcc/match.pd b/gcc/match.pd
index ec2038d48dc4..362bcac291fd 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.  */