Internal-fn: Support new IFN SAT_TRUNC for unsigned scalar int

This patch would like to add the middle-end presentation for the
saturation truncation.  Aka set the result of truncated value to
the max value when overflow.  It will take the pattern similar
as below.

Form 1:
  #define DEF_SAT_U_TRUC_FMT_1(WT, NT) \
  NT __attribute__((noinline))         \
  sat_u_truc_##T##_fmt_1 (WT x)        \
  {                                    \
    bool overflow = x > (WT)(NT)(-1);  \
    return ((NT)x) | (NT)-overflow;    \
  }

For example, truncated uint16_t to uint8_t, we have

* SAT_TRUNC (254)   => 254
* SAT_TRUNC (255)   => 255
* SAT_TRUNC (256)   => 255
* SAT_TRUNC (65536) => 255

Given below SAT_TRUNC from uint64_t to uint32_t.

DEF_SAT_U_TRUC_FMT_1 (uint64_t, uint32_t)

Before this patch:
__attribute__((noinline))
uint32_t sat_u_truc_T_fmt_1 (uint64_t x)
{
  _Bool overflow;
  unsigned int _1;
  unsigned int _2;
  unsigned int _3;
  uint32_t _6;

;;   basic block 2, loop depth 0
;;    pred:       ENTRY
  overflow_5 = x_4(D) > 4294967295;
  _1 = (unsigned int) x_4(D);
  _2 = (unsigned int) overflow_5;
  _3 = -_2;
  _6 = _1 | _3;
  return _6;
;;    succ:       EXIT

}

After this patch:
__attribute__((noinline))
uint32_t sat_u_truc_T_fmt_1 (uint64_t x)
{
  uint32_t _6;

;;   basic block 2, loop depth 0
;;    pred:       ENTRY
  _6 = .SAT_TRUNC (x_4(D)); [tail call]
  return _6;
;;    succ:       EXIT

}

The below tests are passed for this patch:
*. The rv64gcv fully regression tests.
*. The rv64gcv build with glibc.
*. The x86 bootstrap tests.
*. The x86 fully regression tests.

gcc/ChangeLog:

	* internal-fn.def (SAT_TRUNC): Add new signed IFN sat_trunc as
	unary_convert.
	* match.pd: Add new matching pattern for unsigned int sat_trunc.
	* optabs.def (OPTAB_CL): Add unsigned and signed optab.
	* tree-ssa-math-opts.cc (gimple_unsigend_integer_sat_trunc): Add
	new decl for the matching pattern generated func.
	(match_unsigned_saturation_trunc): Add new func impl to match
	the .SAT_TRUNC.
	(math_opts_dom_walker::after_dom_children): Add .SAT_TRUNC match
	function under BIT_IOR_EXPR case.

Signed-off-by: Pan Li <pan2.li@intel.com>

4 files changed, 53 insertions, 0 deletions

diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
index a8c8343..915d329 100644
--- a/gcc/internal-fn.def
+++ b/gcc/internal-fn.def
@@ -278,6 +278,8 @@ DEF_INTERNAL_SIGNED_OPTAB_FN (MULHRS, ECF_CONST | ECF_NOTHROW, first,
 DEF_INTERNAL_SIGNED_OPTAB_FN (SAT_ADD, ECF_CONST, first, ssadd, usadd, binary)
 DEF_INTERNAL_SIGNED_OPTAB_FN (SAT_SUB, ECF_CONST, first, sssub, ussub, binary)
 
+DEF_INTERNAL_SIGNED_OPTAB_FN (SAT_TRUNC, ECF_CONST, first, sstrunc, ustrunc, unary_convert)
+
 DEF_INTERNAL_COND_FN (ADD, ECF_CONST, add, binary)
 DEF_INTERNAL_COND_FN (SUB, ECF_CONST, sub, binary)
 DEF_INTERNAL_COND_FN (MUL, ECF_CONST, smul, binary)
diff --git a/gcc/match.pd b/gcc/match.pd
index 820591a..3fa3f2e 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3210,6 +3210,22 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
       && types_match (type, @0, @1))))
 
+/* Unsigned saturation truncate, case 1 (), sizeof (WT) > sizeof (NT).
+   SAT_U_TRUNC = (NT)x | (NT)(-(X > (WT)(NT)(-1))).  */
+(match (unsigned_integer_sat_trunc @0)
+ (bit_ior:c (negate (convert (gt @0 INTEGER_CST@1)))
+   (convert @0))
+ (with {
+   unsigned itype_precision = TYPE_PRECISION (TREE_TYPE (@0));
+   unsigned otype_precision = TYPE_PRECISION (type);
+   wide_int trunc_max = wi::mask (itype_precision / 2, false, itype_precision);
+   wide_int int_cst = wi::to_wide (@1, itype_precision);
+  }
+  (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
+       && TYPE_UNSIGNED (TREE_TYPE (@0))
+       && otype_precision < itype_precision
+       && wi::eq_p (trunc_max, int_cst)))))
+
 /* x >  y  &&  x != XXX_MIN  -->  x > y
    x >  y  &&  x == XXX_MIN  -->  false . */
 (for eqne (eq ne)
diff --git a/gcc/optabs.def b/gcc/optabs.def
index 2f36ed4..a69af51 100644
--- a/gcc/optabs.def
+++ b/gcc/optabs.def
@@ -63,6 +63,9 @@ OPTAB_CX(fractuns_optab, "fractuns$Q$b$I$a2")
 OPTAB_CL(satfract_optab, "satfract$b$Q$a2", SAT_FRACT, "satfract", gen_satfract_conv_libfunc)
 OPTAB_CL(satfractuns_optab, "satfractuns$I$b$Q$a2", UNSIGNED_SAT_FRACT, "satfractuns", gen_satfractuns_conv_libfunc)
 
+OPTAB_CL(ustrunc_optab, "ustrunc$b$a2", US_TRUNCATE, "ustrunc", NULL)
+OPTAB_CL(sstrunc_optab, "sstrunc$b$a2", SS_TRUNCATE, "sstrunc", NULL)
+
 OPTAB_CD(sfixtrunc_optab, "fix_trunc$F$b$I$a2")
 OPTAB_CD(ufixtrunc_optab, "fixuns_trunc$F$b$I$a2")
 
diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index 5708548..3783a87 100644
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -4088,6 +4088,7 @@ arith_overflow_check_p (gimple *stmt, gimple *cast_stmt, gimple *&use_stmt,
 
 extern bool gimple_unsigned_integer_sat_add (tree, tree*, tree (*)(tree));
 extern bool gimple_unsigned_integer_sat_sub (tree, tree*, tree (*)(tree));
+extern bool gimple_unsigned_integer_sat_trunc (tree, tree*, tree (*)(tree));
 
 static void
 build_saturation_binary_arith_call (gimple_stmt_iterator *gsi, internal_fn fn,
@@ -4216,6 +4217,36 @@ match_unsigned_saturation_sub (gimple_stmt_iterator *gsi, gphi *phi)
 					ops[0], ops[1]);
 }
 
+/*
+ * Try to match saturation unsigned sub.
+ * uint16_t x_4(D);
+ * uint8_t _6;
+ * overflow_5 = x_4(D) > 255;
+ * _1 = (unsigned char) x_4(D);
+ * _2 = (unsigned char) overflow_5;
+ * _3 = -_2;
+ * _6 = _1 | _3;
+ * =>
+ * _6 = .SAT_TRUNC (x_4(D));
+ * */
+static void
+match_unsigned_saturation_trunc (gimple_stmt_iterator *gsi, gassign *stmt)
+{
+  tree ops[1];
+  tree lhs = gimple_assign_lhs (stmt);
+  tree type = TREE_TYPE (lhs);
+
+  if (gimple_unsigned_integer_sat_trunc (lhs, ops, NULL)
+    && direct_internal_fn_supported_p (IFN_SAT_TRUNC,
+				       tree_pair (type, TREE_TYPE (ops[0])),
+				       OPTIMIZE_FOR_BOTH))
+    {
+      gcall *call = gimple_build_call_internal (IFN_SAT_TRUNC, 1, ops[0]);
+      gimple_call_set_lhs (call, lhs);
+      gsi_replace (gsi, call, /* update_eh_info */ true);
+    }
+}
+
 /* Recognize for unsigned x
    x = y - z;
    if (x > y)
@@ -6188,6 +6219,7 @@ math_opts_dom_walker::after_dom_children (basic_block bb)
 
 	    case BIT_IOR_EXPR:
 	      match_unsigned_saturation_add (&gsi, as_a<gassign *> (stmt));
+	      match_unsigned_saturation_trunc (&gsi, as_a<gassign *> (stmt));
 	      /* fall-through  */
 	    case BIT_XOR_EXPR:
 	      match_uaddc_usubc (&gsi, stmt, code);