[PATCH v1 1/2] Match: Support branch form for unsigned SAT_ADD

[pan2.li@intel.com]

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

This patch would like to support the branch form for unsigned
SAT_ADD.  For example as below:

uint64_t
sat_add (uint64_t x, uint64_t y)
{
  return (uint64_t) (x + y) >= x ? (x + y) : -1;
}

Different to the branchless version,  we leverage the simplify to
convert the branch version of SAT_ADD into branchless if and only
if the backend has supported the IFN_SAT_ADD.  Thus,  the backend has
the ability to choose branch or branchless implementation of .SAT_ADD.
For example,  some target can take care of branches code more optimally.

When the target implement the IFN_SAT_ADD for unsigned and before this
patch:
uint64_t sat_add_u_1_uint64_t (uint64_t x, uint64_t y)
{
  long unsigned int _1;
  uint64_t _2;
  __complex__ long unsigned int _6;
  long unsigned int _7;

;;   basic block 2, loop depth 0
;;    pred:       ENTRY
  _6 = .ADD_OVERFLOW (x_3(D), y_4(D));
  _1 = REALPART_EXPR <_6>;
  _7 = IMAGPART_EXPR <_6>;
  if (_7 == 0)
    goto <bb 4>; [65.00%]
  else
    goto <bb 3>; [35.00%]
;;    succ:       4
;;                3

;;   basic block 3, loop depth 0
;;    pred:       2
;;    succ:       4

;;   basic block 4, loop depth 0
;;    pred:       3
;;                2
  # _2 = PHI <18446744073709551615(3), _1(2)>
  return _2;
;;    succ:       EXIT

}

After this patch:
uint64_t sat_add (uint64_t x, uint64_t y)
{
  long unsigned int _9;

;;   basic block 2, loop depth 0
;;    pred:       ENTRY
  _9 = .SAT_ADD (x_3(D), y_4(D)); [tail call]
  return _9;
;;    succ:       EXIT
}

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

gcc/ChangeLog:

	* match.pd: Add new simplify to convert branch SAT_ADD into
	branchless,  if and only if backend implement the IFN.

Signed-off-by: Pan Li <pan2.li@intel.com>
---
 gcc/match.pd | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/gcc/match.pd b/gcc/match.pd
index 0f9c34fa897..0547b57b3a3 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3094,6 +3094,24 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 (match (unsigned_integer_sat_add @0 @1)
  (bit_ior:c (usadd_left_part_2 @0 @1) (usadd_right_part_2 @0 @1)))
 
+#if GIMPLE
+
+/* Simplify the branch version of SAT_ADD into branchless if and only if
+   the backend has supported the IFN_SAT_ADD.  Thus, the backend has the
+   ability to choose branch or branchless implementation of .SAT_ADD.  */
+
+(simplify
+ (cond (ge (plus:c@2 @0 @1) @0) @2 integer_minus_onep)
+  (if (direct_internal_fn_supported_p (IFN_SAT_ADD, type, OPTIMIZE_FOR_BOTH))
+   (bit_ior @2 (negate (convert (lt @2 @0))))))
+
+(simplify
+ (cond (le @0 (plus:c@2 @0 @1)) @2 integer_minus_onep)
+  (if (direct_internal_fn_supported_p (IFN_SAT_ADD, type, OPTIMIZE_FOR_BOTH))
+   (bit_ior @2 (negate (convert (lt @2 @0))))))
+
+#endif
+
 /* x >  y  &&  x != XXX_MIN  -->  x > y
    x >  y  &&  x == XXX_MIN  -->  false . */
 (for eqne (eq ne)
-- 
2.34.1