Match: Support more form for scalar unsigned SAT_ADD

After we support one gassign form of the unsigned .SAT_ADD,  we
would like to support more forms including both the branch and
branchless.  There are 5 other forms of .SAT_ADD,  list as below:

Form 1:
  #define SAT_ADD_U_1(T) \
  T sat_add_u_1_##T(T x, T y) \
  { \
    return (T)(x + y) >= x ? (x + y) : -1; \
  }

Form 2:
  #define SAT_ADD_U_2(T) \
  T sat_add_u_2_##T(T x, T y) \
  { \
    T ret; \
    T overflow = __builtin_add_overflow (x, y, &ret); \
    return (T)(-overflow) | ret; \
  }

Form 3:
  #define SAT_ADD_U_3(T) \
  T sat_add_u_3_##T (T x, T y) \
  { \
    T ret; \
    return __builtin_add_overflow (x, y, &ret) ? -1 : ret; \
  }

Form 4:
  #define SAT_ADD_U_4(T) \
  T sat_add_u_4_##T (T x, T y) \
  { \
    T ret; \
    return __builtin_add_overflow (x, y, &ret) == 0 ? ret : -1; \
  }

Form 5:
  #define SAT_ADD_U_5(T) \
  T sat_add_u_5_##T(T x, T y) \
  { \
    return (T)(x + y) < x ? -1 : (x + y); \
  }

Take the forms 3 of above as example:

uint64_t
sat_add (uint64_t x, uint64_t y)
{
  uint64_t ret;
  return __builtin_add_overflow (x, y, &ret) ? -1 : ret;
}

Before this patch:
uint64_t sat_add (uint64_t x, uint64_t y)
{
  long unsigned int _1;
  long unsigned int _2;
  uint64_t _3;
  __complex__ long unsigned int _6;

;;   basic block 2, loop depth 0
;;    pred:       ENTRY
  _6 = .ADD_OVERFLOW (x_4(D), y_5(D));
  _2 = IMAGPART_EXPR <_6>;
  if (_2 != 0)
    goto <bb 4>; [35.00%]
  else
    goto <bb 3>; [65.00%]
;;    succ:       4
;;                3

;;   basic block 3, loop depth 0
;;    pred:       2
  _1 = REALPART_EXPR <_6>;
;;    succ:       4

;;   basic block 4, loop depth 0
;;    pred:       3
;;                2
  # _3 = PHI <_1(3), 18446744073709551615(2)>
  return _3;
;;    succ:       EXIT
}

After this patch:
uint64_t sat_add (uint64_t x, uint64_t y)
{
  long unsigned int _12;

;;   basic block 2, loop depth 0
;;    pred:       ENTRY
  _12 = .SAT_ADD (x_4(D), y_5(D)); [tail call]
  return _12;
;;    succ:       EXIT
}

The flag '^' acts on cond_expr will generate matching code similar as below:

else if (gphi *_a1 = dyn_cast <gphi *> (_d1))
  {
    basic_block _b1 = gimple_bb (_a1);
    if (gimple_phi_num_args (_a1) == 2)
      {
        basic_block _pb_0_1 = EDGE_PRED (_b1, 0)->src;
        basic_block _pb_1_1 = EDGE_PRED (_b1, 1)->src;
        basic_block _db_1 = safe_dyn_cast <gcond *> (*gsi_last_bb (_pb_0_1))
                            ? _pb_0_1 : _pb_1_1;
        basic_block _other_db_1 = safe_dyn_cast <gcond *> (*gsi_last_bb (_pb_0_1))
                                  ? _pb_1_1 : _pb_0_1;
        gcond *_ct_1 = safe_dyn_cast <gcond *> (*gsi_last_bb (_db_1));
        if (_ct_1 && EDGE_COUNT (_other_db_1->preds) == 1
          && EDGE_COUNT (_other_db_1->succs) == 1
          && EDGE_PRED (_other_db_1, 0)->src == _db_1)
          {
            tree _cond_lhs_1 = gimple_cond_lhs (_ct_1);
            tree _cond_rhs_1 = gimple_cond_rhs (_ct_1);
            tree _p0 = build2 (gimple_cond_code (_ct_1), boolean_type_node,
                               _cond_lhs_1, _cond_rhs_1);
            bool _arg_0_is_true_1 = gimple_phi_arg_edge (_a1, 0)->flags & EDGE_TRUE_VALUE;
            tree _p1 = gimple_phi_arg_def (_a1, _arg_0_is_true_1 ? 0 : 1);
            tree _p2 = gimple_phi_arg_def (_a1, _arg_0_is_true_1 ? 1 : 0);
            ....

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:

	* doc/match-and-simplify.texi: Add doc for the matching flag '^'.
	* genmatch.cc (cmp_operand): Add match_phi comparation.
	(dt_node::gen_kids_1): Add cond_expr bool flag for phi match.
	(dt_operand::gen_phi_on_cond): Add new func to gen phi matching
	on cond_expr.
	(parser::parse_expr): Add handling for the expr flag '^'.
	* match.pd: Add more form for unsigned .SAT_ADD.
	* tree-ssa-math-opts.cc (build_saturation_binary_arith_call): Add
	new func impl to build call for phi gimple.
	(match_unsigned_saturation_add): Add new func impl to match the
	.SAT_ADD for phi gimple.
	(math_opts_dom_walker::after_dom_children): Add phi matching
	try for all gimple phi stmt.

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

4 files changed, 236 insertions, 5 deletions

diff --git a/gcc/doc/match-and-simplify.texi b/gcc/doc/match-and-simplify.texi
index 01f19e2..63d5af1 100644
--- a/gcc/doc/match-and-simplify.texi
+++ b/gcc/doc/match-and-simplify.texi
@@ -361,6 +361,22 @@ Usually the types of the generated result expressions are
 determined from the context, but sometimes like in the above case
 it is required that you specify them explicitly.
 
+Another modifier for generated expressions is @code{^} which
+tells the machinery to try more matches for some special cases.
+For example, normally the @code{cond} only allows the gimple
+assign when matching.  It will also try to match the gimple @code{PHI}
+besides gimple assign if appending the @code{^} to the @code{cond}.
+Aka @code{cond^}.  Consider below example
+
+@smallexample
+(match (unsigned_sat_add @@0 @@1)
+ (cond^ (ge (plus:c@@2 @@0 @@1) @@0) @@2 integer_minus_onep))
+@end smallexample
+
+The above matching will generate the predicate function named
+@code{gimple_unsigned_sat_add} that accepts both the gimple
+assign and gimple @code{PHI}.
+
 Another modifier for generated expressions is @code{!} which
 tells the machinery to only consider the simplification in case
 the marked expression simplified to a simple operand.  Consider
diff --git a/gcc/genmatch.cc b/gcc/genmatch.cc
index f1e0e7a..a56bd90 100644
--- a/gcc/genmatch.cc
+++ b/gcc/genmatch.cc
@@ -848,12 +848,13 @@ public:
     : operand (OP_EXPR, loc), operation (operation_),
       ops (vNULL), expr_type (NULL), is_commutative (is_commutative_),
       is_generic (false), force_single_use (false), force_leaf (false),
-      opt_grp (0) {}
+      match_phi (false), opt_grp (0) {}
   expr (expr *e)
     : operand (OP_EXPR, e->location), operation (e->operation),
       ops (vNULL), expr_type (e->expr_type), is_commutative (e->is_commutative),
       is_generic (e->is_generic), force_single_use (e->force_single_use),
-      force_leaf (e->force_leaf), opt_grp (e->opt_grp) {}
+      force_leaf (e->force_leaf), match_phi (e->match_phi),
+      opt_grp (e->opt_grp) {}
   void append_op (operand *op) { ops.safe_push (op); }
   /* The operator and its operands.  */
   id_base *operation;
@@ -871,6 +872,8 @@ public:
   /* Whether in the result expression this should be a leaf node
      with any children simplified down to simple operands.  */
   bool force_leaf;
+  /* Whether the COND_EXPR is matching PHI gimple,  default false.  */
+  bool match_phi;
   /* If non-zero, the group for optional handling.  */
   unsigned char opt_grp;
   void gen_transform (FILE *f, int, const char *, bool, int,
@@ -1819,6 +1822,7 @@ public:
 
   char *get_name (char *);
   void gen_opname (char *, unsigned);
+  void gen_phi_on_cond (FILE *, int, int);
 };
 
 /* Leaf node of the decision tree, used for DT_SIMPLIFY.  */
@@ -1898,7 +1902,8 @@ cmp_operand (operand *o1, operand *o2)
       expr *e1 = static_cast<expr *>(o1);
       expr *e2 = static_cast<expr *>(o2);
       if (e1->operation != e2->operation
-	  || e1->is_generic != e2->is_generic)
+	  || e1->is_generic != e2->is_generic
+	  || e1->match_phi != e2->match_phi)
 	return false;
       if (e1->operation->kind == id_base::FN
 	  /* For function calls also compare number of arguments.  */
@@ -3251,6 +3256,7 @@ dt_node::gen_kids_1 (FILE *f, int indent, bool gimple, int depth,
 			  depth);
 	  indent += 4;
 	  fprintf_indent (f, indent, "{\n");
+	  bool cond_expr_p = false;
 	  for (unsigned i = 0; i < exprs_len; ++i)
 	    {
 	      expr *e = as_a <expr *> (gimple_exprs[i]->op);
@@ -3262,6 +3268,7 @@ dt_node::gen_kids_1 (FILE *f, int indent, bool gimple, int depth,
 	      else
 		{
 		  id_base *op = e->operation;
+		  cond_expr_p |= (*op == COND_EXPR && e->match_phi);
 		  if (*op == CONVERT_EXPR || *op == NOP_EXPR)
 		    fprintf_indent (f, indent, "CASE_CONVERT:\n");
 		  else
@@ -3275,6 +3282,27 @@ dt_node::gen_kids_1 (FILE *f, int indent, bool gimple, int depth,
 	  fprintf_indent (f, indent, "default:;\n");
 	  fprintf_indent (f, indent, "}\n");
 	  indent -= 4;
+
+	  if (cond_expr_p)
+	    {
+	      fprintf_indent (f, indent,
+		"else if (gphi *_a%d = dyn_cast <gphi *> (_d%d))\n",
+		depth, depth);
+	      indent += 2;
+	      fprintf_indent (f, indent, "{\n");
+	      indent += 2;
+
+	      for (unsigned i = 0; i < exprs_len; i++)
+		{
+		  expr *e = as_a <expr *> (gimple_exprs[i]->op);
+		  if (*e->operation == COND_EXPR && e->match_phi)
+		    gimple_exprs[i]->gen_phi_on_cond (f, indent, depth);
+		}
+
+	      indent -= 2;
+	      fprintf_indent (f, indent, "}\n");
+	      indent -= 2;
+	    }
 	}
 
       if (fns_len)
@@ -3483,6 +3511,86 @@ dt_operand::gen (FILE *f, int indent, bool gimple, int depth)
     }
 }
 
+/* Generate matching code for the phi when meet COND_EXPR.  */
+
+void
+dt_operand::gen_phi_on_cond (FILE *f, int indent, int depth)
+{
+  fprintf_indent (f, indent,
+    "basic_block _b%d = gimple_bb (_a%d);\n", depth, depth);
+
+  fprintf_indent (f, indent, "if (gimple_phi_num_args (_a%d) == 2)\n", depth);
+
+  indent += 2;
+  fprintf_indent (f, indent, "{\n");
+  indent += 2;
+
+  fprintf_indent (f, indent,
+    "basic_block _pb_0_%d = EDGE_PRED (_b%d, 0)->src;\n", depth, depth);
+  fprintf_indent (f, indent,
+    "basic_block _pb_1_%d = EDGE_PRED (_b%d, 1)->src;\n", depth, depth);
+  fprintf_indent (f, indent,
+    "basic_block _db_%d = safe_dyn_cast <gcond *> (*gsi_last_bb (_pb_0_%d)) ? "
+    "_pb_0_%d : _pb_1_%d;\n", depth, depth, depth, depth);
+  fprintf_indent (f, indent,
+    "basic_block _other_db_%d = safe_dyn_cast <gcond *> "
+    "(*gsi_last_bb (_pb_0_%d)) ? _pb_1_%d : _pb_0_%d;\n",
+    depth, depth, depth, depth);
+
+  fprintf_indent (f, indent,
+    "gcond *_ct_%d = safe_dyn_cast <gcond *> (*gsi_last_bb (_db_%d));\n",
+    depth, depth);
+  fprintf_indent (f, indent, "if (_ct_%d"
+    " && EDGE_COUNT (_other_db_%d->preds) == 1\n", depth, depth);
+  fprintf_indent (f, indent,
+    "  && EDGE_COUNT (_other_db_%d->succs) == 1\n", depth);
+  fprintf_indent (f, indent,
+    "  && EDGE_PRED (_other_db_%d, 0)->src == _db_%d)\n", depth, depth);
+
+  indent += 2;
+  fprintf_indent (f, indent, "{\n");
+  indent += 2;
+
+  fprintf_indent (f, indent,
+    "tree _cond_lhs_%d = gimple_cond_lhs (_ct_%d);\n", depth, depth);
+  fprintf_indent (f, indent,
+    "tree _cond_rhs_%d = gimple_cond_rhs (_ct_%d);\n", depth, depth);
+
+  char opname_0[20];
+  char opname_1[20];
+  char opname_2[20];
+  gen_opname (opname_0, 0);
+
+  fprintf_indent (f, indent,
+    "tree %s = build2 (gimple_cond_code (_ct_%d), "
+    "boolean_type_node, _cond_lhs_%d, _cond_rhs_%d);\n",
+    opname_0, depth, depth, depth);
+
+  fprintf_indent (f, indent,
+    "bool _arg_0_is_true_%d = gimple_phi_arg_edge (_a%d, 0)->flags"
+    " & EDGE_TRUE_VALUE;\n", depth, depth);
+
+  gen_opname (opname_1, 1);
+  fprintf_indent (f, indent,
+    "tree %s = gimple_phi_arg_def (_a%d, _arg_0_is_true_%d ? 0 : 1);\n",
+    opname_1, depth, depth);
+
+  gen_opname (opname_2, 2);
+  fprintf_indent (f, indent,
+    "tree %s = gimple_phi_arg_def (_a%d, _arg_0_is_true_%d ? 1 : 0);\n",
+    opname_2, depth, depth);
+
+  gen_kids (f, indent, true, depth);
+
+  indent -= 2;
+  fprintf_indent (f, indent, "}\n");
+  indent -= 2;
+
+  indent -= 2;
+  fprintf_indent (f, indent, "}\n");
+  indent -= 2;
+}
+
 /* Emit a logging call to the debug file to the file F, with the INDENT from
    either the RESULT location or the S's match location if RESULT is null. */
 static void
@@ -4600,6 +4708,18 @@ parser::parse_expr ()
       e->force_leaf = true;
     }
 
+  if (token->type == CPP_XOR && !(token->flags & PREV_WHITE))
+    {
+      if (!parsing_match_operand)
+	fatal_at (token, "modifier '^' is only valid in a match expression");
+
+      if (!(*e->operation == COND_EXPR))
+	fatal_at (token, "modifier '^' can only act on operation COND_EXPR");
+
+      eat_token (CPP_XOR);
+      e->match_phi = true;
+    }
+
   if (token->type == CPP_COLON
       && !(token->flags & PREV_WHITE))
     {
diff --git a/gcc/match.pd b/gcc/match.pd
index ebc60eb..5cfe81e 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3056,31 +3056,48 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
       && wi::eq_p (wi::to_wide (int_cst), wi::max_value (itype))))))
 
 /* Unsigned Saturation Add */
+/* SAT_ADD = usadd_left_part_1 | usadd_right_part_1, aka:
+   SAT_ADD = (X + Y) | -((X + Y) < X)  */
 (match (usadd_left_part_1 @0 @1)
  (plus:c @0 @1)
  (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
       && types_match (type, @0, @1))))
 
+/* SAT_ADD = usadd_left_part_2 | usadd_right_part_2, aka:
+   SAT_ADD = REALPART_EXPR <.ADD_OVERFLOW> | (IMAGPART_EXPR <.ADD_OVERFLOW> != 0) */
 (match (usadd_left_part_2 @0 @1)
  (realpart (IFN_ADD_OVERFLOW:c @0 @1))
  (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
       && types_match (type, @0, @1))))
 
+/* SAT_ADD = usadd_left_part_1 | usadd_right_part_1, aka:
+   SAT_ADD = (X + Y) | -((type)(X + Y) < X)  */
 (match (usadd_right_part_1 @0 @1)
  (negate (convert (lt (plus:c @0 @1) @0)))
  (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
       && types_match (type, @0, @1))))
 
+/* SAT_ADD = usadd_left_part_1 | usadd_right_part_1, aka:
+   SAT_ADD = (X + Y) | -(X > (X + Y))  */
 (match (usadd_right_part_1 @0 @1)
  (negate (convert (gt @0 (plus:c @0 @1))))
  (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
       && types_match (type, @0, @1))))
 
+/* SAT_ADD = usadd_left_part_2 | usadd_right_part_2, aka:
+   SAT_ADD = REALPART_EXPR <.ADD_OVERFLOW> | (IMAGPART_EXPR <.ADD_OVERFLOW> != 0) */
 (match (usadd_right_part_2 @0 @1)
  (negate (convert (ne (imagpart (IFN_ADD_OVERFLOW:c @0 @1)) integer_zerop)))
  (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
       && types_match (type, @0, @1))))
 
+/* SAT_ADD = usadd_left_part_2 | usadd_right_part_2, aka:
+   SAT_ADD = REALPART_EXPR <.ADD_OVERFLOW> | -IMAGPART_EXPR <.ADD_OVERFLOW> */
+(match (usadd_right_part_2 @0 @1)
+ (negate (imagpart (IFN_ADD_OVERFLOW:c @0 @1)))
+ (if (INTEGRAL_TYPE_P (type) && TYPE_UNSIGNED (type)
+      && types_match (type, @0, @1))))
+
 /* We cannot merge or overload usadd_left_part_1 and usadd_left_part_2
    because the sub part of left_part_2 cannot work with right_part_1.
    For example, left_part_2 pattern focus one .ADD_OVERFLOW but the
@@ -3092,10 +3109,34 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 (match (unsigned_integer_sat_add @0 @1)
  (bit_ior:c (usadd_left_part_1 @0 @1) (usadd_right_part_1 @0 @1)))
 
-/* Unsigned saturation add, case 2 (branchless with .ADD_OVERFLOW).  */
+/* Unsigned saturation add, case 2 (branchless with .ADD_OVERFLOW):
+   SAT_ADD = REALPART_EXPR <.ADD_OVERFLOW> | -IMAGPART_EXPR <.ADD_OVERFLOW> or
+   SAT_ADD = REALPART_EXPR <.ADD_OVERFLOW> | (IMAGPART_EXPR <.ADD_OVERFLOW> != 0) */
 (match (unsigned_integer_sat_add @0 @1)
  (bit_ior:c (usadd_left_part_2 @0 @1) (usadd_right_part_2 @0 @1)))
 
+/* Unsigned saturation add, case 3 (branch with ge):
+   SAT_U_ADD = (X + Y) >= x ? (X + Y) : -1.  */
+(match (unsigned_integer_sat_add @0 @1)
+ (cond^ (ge (usadd_left_part_1@2 @0 @1) @0) @2 integer_minus_onep))
+
+/* Unsigned saturation add, case 4 (branch with lt):
+   SAT_U_ADD = (X + Y) < x ? -1 : (X + Y).  */
+(match (unsigned_integer_sat_add @0 @1)
+ (cond^ (lt (usadd_left_part_1@2 @0 @1) @0) integer_minus_onep @2))
+
+/* Unsigned saturation add, case 5 (branch with eq .ADD_OVERFLOW):
+   SAT_U_ADD = REALPART_EXPR <.ADD_OVERFLOW> == 0 ? .ADD_OVERFLOW : -1.  */
+(match (unsigned_integer_sat_add @0 @1)
+ (cond^ (eq (imagpart (IFN_ADD_OVERFLOW:c @0 @1)) integer_zerop)
+  (usadd_left_part_2 @0 @1) integer_minus_onep))
+
+/* Unsigned saturation add, case 6 (branch with ne .ADD_OVERFLOW):
+   SAT_U_ADD = REALPART_EXPR <.ADD_OVERFLOW> != 0 ? -1 : .ADD_OVERFLOW.  */
+(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 sub, case 1 (branch with gt):
    SAT_U_SUB = X > Y ? X - Y : 0  */
 (match (unsigned_integer_sat_sub @0 @1)
diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index 469e34d..173b036 100644
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -4101,8 +4101,24 @@ build_saturation_binary_arith_call (gimple_stmt_iterator *gsi, internal_fn fn,
     }
 }
 
+static void
+build_saturation_binary_arith_call (gimple_stmt_iterator *gsi, gphi *phi,
+				    internal_fn fn, tree lhs, tree op_0,
+				    tree op_1)
+{
+  if (direct_internal_fn_supported_p (fn, TREE_TYPE (lhs), OPTIMIZE_FOR_BOTH))
+    {
+      gcall *call = gimple_build_call_internal (fn, 2, op_0, op_1);
+      gimple_call_set_lhs (call, lhs);
+      gsi_insert_before (gsi, call, GSI_SAME_STMT);
+
+      gimple_stmt_iterator psi = gsi_for_stmt (phi);
+      remove_phi_node (&psi, /* release_lhs_p */ false);
+    }
+}
+
 /*
- * Try to match saturation unsigned add.
+ * Try to match saturation unsigned add with assign.
  *   _7 = _4 + _6;
  *   _8 = _4 > _7;
  *   _9 = (long unsigned int) _8;
@@ -4122,6 +4138,37 @@ match_unsigned_saturation_add (gimple_stmt_iterator *gsi, gassign *stmt)
 }
 
 /*
+ * Try to match saturation unsigned add with PHI.
+ *   <bb 2> :
+ *   _1 = x_3(D) + y_4(D);
+ *   if (_1 >= x_3(D))
+ *     goto <bb 3>; [INV]
+ *   else
+ *     goto <bb 4>; [INV]
+ *
+ *   <bb 3> :
+ *
+ *   <bb 4> :
+ *   # _2 = PHI <255(2), _1(3)>
+ *   =>
+ *   <bb 4> [local count: 1073741824]:
+ *   _2 = .SAT_ADD (x_4(D), y_5(D));  */
+
+static void
+match_unsigned_saturation_add (gimple_stmt_iterator *gsi, gphi *phi)
+{
+  if (gimple_phi_num_args (phi) != 2)
+    return;
+
+  tree ops[2];
+  tree phi_result = gimple_phi_result (phi);
+
+  if (gimple_unsigned_integer_sat_add (phi_result, ops, NULL))
+    build_saturation_binary_arith_call (gsi, phi, IFN_SAT_ADD, phi_result,
+					ops[0], ops[1]);
+}
+
+/*
  * Try to match saturation unsigned sub.
  *   _1 = _4 >= _5;
  *   _3 = _4 - _5;
@@ -6052,6 +6099,13 @@ math_opts_dom_walker::after_dom_children (basic_block bb)
 
   fma_deferring_state fma_state (param_avoid_fma_max_bits > 0);
 
+  for (gphi_iterator psi = gsi_start_phis (bb); !gsi_end_p (psi);
+    gsi_next (&psi))
+    {
+      gimple_stmt_iterator gsi = gsi_last_bb (bb);
+      match_unsigned_saturation_add (&gsi, psi.phi ());
+    }
+
   for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi);)
     {
       gimple *stmt = gsi_stmt (gsi);