From: Pan Li <pan2...@intel.com>

There are sorts of forms for the unsigned SAT_ADD.  Some of them are
complicated while others are cheap.  This patch would like to simplify
the complicated form into the cheap ones.  For example as below:

>From the form 6 (branch):
  SUM = ADD_OVERFLOW (X, Y)
  SAT_U_ADD = IMAGPART_EXPR (SUM) != 0 ? -1 : REALPART_EXPR (SUM)

To (branchless):
  SAT_U_ADD = (X + Y) | - ((X + Y) < X).

  #define T uint8_t

  T sat_add_u_1 (T x, T y)
  {
    T ret;
    return __builtin_add_overflow (x, y, &ret) != 0 ? -1 : ret;
  }

Before this patch in phiopt2:
   4   │ uint8_t sat_u_add_uint8_t_13 (uint8_t x, uint8_t y)
   5   │ {
   6   │   unsigned char _1;
   7   │   unsigned char _2;
   8   │   uint8_t _3;
   9   │   __complex__ unsigned char _6;
  10   │
  11   │   <bb 2> [local count: 1073741824]:
  12   │   _6 = .ADD_OVERFLOW (x_4(D), y_5(D));
  13   │   _1 = REALPART_EXPR <_6>;
  14   │   _2 = IMAGPART_EXPR <_6>;
  15   │   if (_2 != 0)
  16   │     goto <bb 4>; [35.00%]
  17   │   else
  18   │     goto <bb 3>; [65.00%]
  19   │
  20   │   <bb 3> [local count: 697932184]:
  21   │
  22   │   <bb 4> [local count: 1073741824]:
  23   │   # _3 = PHI <_1(3), 255(2)>
  24   │   return _3;
  25   │
  26   │ }

After this patch:
  14   │ uint8_t sat_u_add_uint8_t_13 (uint8_t x, uint8_t y)
  15   │ {
  16   │   unsigned char _1;
  17   │   __complex__ unsigned char _6;
  18   │   unsigned char _8;
  19   │   _Bool _9;
  20   │   unsigned char _10;
  21   │   unsigned char _11;
  22   │   unsigned char _12;
  23   │
  24   │   <bb 2> [local count: 1073741824]:
  25   │   _6 = .ADD_OVERFLOW (x_4(D), y_5(D)); // Dead code
  26   │   _1 = REALPART_EXPR <_6>;             // Ditto
  27   │   _8 = x_4(D) + y_5(D);
  28   │   _9 = x_4(D) > _8;
  29   │   _10 = (unsigned char) _9;
  30   │   _11 = -_10;
  31   │   _12 = _8 | _11;
  32   │   return _12;
  33   │
  34   │ }

The below test suites are passed for this patch.
* The rv64gcv fully regression test.
* The x86 bootstrap test.
* The x86 fully regression test.

gcc/ChangeLog:

        * match.pd: Remove unsigned branch form 6 for SAT_ADD, and
        add simplify to branchless instead.

Signed-off-by: Pan Li <pan2...@intel.com>
---
 gcc/match.pd | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/gcc/match.pd b/gcc/match.pd
index 8ed08b95bc0..c360e212340 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3165,16 +3165,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
         SAT_U_ADD = IMAGPART_EXPR (SUM) == 0 ? REALPART_EXPR (SUM) : -1  */
  (simplify (cond (eq (imagpart (IFN_ADD_OVERFLOW:c@2 @0 @1)) integer_zerop)
                 (realpart @2) integer_minus_onep)
+  (if (types_match (type, @0, @1))
+   (bit_ior (plus@3 @0 @1) (negate (convert (lt @3 @0))))))
+ /* From SUM = ADD_OVERFLOW (X, Y)
+        SAT_U_ADD = IMAGPART_EXPR (SUM) != 0 ? -1 : REALPART_EXPR (SUM)  */
+ (simplify (cond (ne (imagpart (IFN_ADD_OVERFLOW:c@2 @0 @1)) integer_zerop)
+                integer_minus_onep (realpart @2))
   (if (types_match (type, @0, @1))
    (bit_ior (plus@3 @0 @1) (negate (convert (lt @3 @0)))))))
 
-/* Unsigned saturation add, case 6 (branch with ne .ADD_OVERFLOW):
-   SUM = ADD_OVERFLOW (X, Y)
-   SAT_U_ADD = IMAGPART_EXPR (SUM) != 0 ? -1 : REALPART_EXPR (SUM).  */
-(match (unsigned_integer_sat_add @0 @1)
- (cond^ (ne (imagpart (IFN_ADD_OVERFLOW:c @0 @1)) integer_zerop)
-  integer_minus_onep (usadd_left_part_2 @0 @1)))
-
 /* Unsigned saturation add, case 9 (one op is imm):
    SAT_U_ADD = (X + 3) >= x ? (X + 3) : -1.  */
 (match (unsigned_integer_sat_add @0 @1)
-- 
2.43.0

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