Avoid some -Wunreachable-code-ctrl

This cleans up unreachable code diagnosed by -Wunreachable-code-ctrl.
It largely follows the previous series but discovers a few extra
cases, namely dead code after break or continue or loops without
exits.

2021-11-29  Richard Biener  <rguenther@suse.de>

gcc/c/
	* gimple-parser.c (c_parser_gimple_postfix_expression):
	avoid unreachable code after break.

gcc/
	* cfgrtl.c (skip_insns_after_block): Refactor code to
	be more easily readable.
	* expr.c (op_by_pieces_d::run): Remove unreachable
	assert.
	* sched-deps.c (sched_analyze): Remove unreachable
	gcc_unreachable.
	* sel-sched-ir.c (in_same_ebb_p): Likewise.
	* tree-ssa-alias.c (nonoverlapping_refs_since_match_p):
	Remove unreachable code.
	* tree-vect-slp.c (vectorize_slp_instance_root_stmt):
	Refactor to avoid unreachable loop iteration.
	* tree.c (walk_tree_1): Remove unreachable break.
	* vec-perm-indices.c (vec_perm_indices::series_p): Remove
	unreachable return.

gcc/cp/
	* parser.c (cp_parser_postfix_expression): Remove
	unreachable code.
	* pt.c (tsubst_expr): Remove unreachable breaks.

gcc/fortran/
	* frontend-passes.c (gfc_expr_walker): Remove unreachable
	break.
	* scanner.c (skip_fixed_comments): Remove unreachable
	gcc_unreachable.
	* trans-expr.c (gfc_expr_is_variable): Refactor to make
	control flow more obvious.

14 files changed, 14 insertions, 59 deletions

diff --git a/gcc/c/gimple-parser.c b/gcc/c/gimple-parser.c
index 32f22db..f594a8c 100644
--- a/gcc/c/gimple-parser.c
+++ b/gcc/c/gimple-parser.c
@@ -1698,13 +1698,7 @@ c_parser_gimple_postfix_expression (gimple_parser &parser)
 	    }
 	  break;
 	}
-      else
-	{
-	  c_parser_error (parser, "expected expression");
-	  expr.set_error ();
-	  break;
-	}
-      break;
+      /* Fallthru.  */
     default:
       c_parser_error (parser, "expected expression");
       expr.set_error ();
diff --git a/gcc/cfgrtl.c b/gcc/cfgrtl.c
index 3744adc..287a3db 100644
--- a/gcc/cfgrtl.c
+++ b/gcc/cfgrtl.c
@@ -3539,14 +3539,8 @@ skip_insns_after_block (basic_block bb)
 	  continue;
 
 	case NOTE:
-	  switch (NOTE_KIND (insn))
-	    {
-	    case NOTE_INSN_BLOCK_END:
-	      gcc_unreachable ();
-	    default:
-	      continue;
-	    }
-	  break;
+	  gcc_assert (NOTE_KIND (insn) != NOTE_INSN_BLOCK_END);
+	  continue;
 
 	case CODE_LABEL:
 	  if (NEXT_INSN (insn)
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 899797b..55e6a1a 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -7892,10 +7892,6 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p,
             return postfix_expression;
 	}
     }
-
-  /* We should never get here.  */
-  gcc_unreachable ();
-  return error_mark_node;
 }
 
 /* Helper function for cp_parser_parenthesized_expression_list and
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 7432370..6e25a38 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -18245,13 +18245,11 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
       stmt = finish_co_yield_expr (input_location,
 				   RECUR (TREE_OPERAND (t, 0)));
       RETURN (stmt);
-      break;
 
     case CO_AWAIT_EXPR:
       stmt = finish_co_await_expr (input_location,
 				   RECUR (TREE_OPERAND (t, 0)));
       RETURN (stmt);
-      break;
 
     case EXPR_STMT:
       tmp = RECUR (EXPR_STMT_EXPR (t));
diff --git a/gcc/expr.c b/gcc/expr.c
index 5673902..b281525 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -1342,9 +1342,6 @@ op_by_pieces_d::run ()
 	}
     }
   while (1);
-
-  /* The code above should have handled everything.  */
-  gcc_assert (!length);
 }
 
 /* Derived class from op_by_pieces_d, providing support for block move
diff --git a/gcc/fortran/frontend-passes.c b/gcc/fortran/frontend-passes.c
index f5ba7ce..16ee2af 100644
--- a/gcc/fortran/frontend-passes.c
+++ b/gcc/fortran/frontend-passes.c
@@ -5229,7 +5229,6 @@ gfc_expr_walker (gfc_expr **e, walk_expr_fn_t exprfn, void *data)
 	  case EXPR_OP:
 	    WALK_SUBEXPR ((*e)->value.op.op1);
 	    WALK_SUBEXPR_TAIL ((*e)->value.op.op2);
-	    break;
 	  case EXPR_FUNCTION:
 	    for (a = (*e)->value.function.actual; a; a = a->next)
 	      WALK_SUBEXPR (a->expr);
diff --git a/gcc/fortran/scanner.c b/gcc/fortran/scanner.c
index 69b81ab..4d72ff7 100644
--- a/gcc/fortran/scanner.c
+++ b/gcc/fortran/scanner.c
@@ -1159,7 +1159,6 @@ skip_fixed_comments (void)
 	  skip_comment_line ();
 	  continue;
 
-	  gcc_unreachable ();
 check_for_digits:
 	  {
 	    /* Required for OpenMP's conditional compilation sentinel. */
diff --git a/gcc/fortran/trans-expr.c b/gcc/fortran/trans-expr.c
index bc502c0..e413b2d 100644
--- a/gcc/fortran/trans-expr.c
+++ b/gcc/fortran/trans-expr.c
@@ -11079,14 +11079,9 @@ gfc_expr_is_variable (gfc_expr *expr)
 	  func_ifc = expr->value.function.esym;
 	  goto found_ifc;
 	}
-      else
-	{
-	  gcc_assert (expr->symtree);
-	  func_ifc = expr->symtree->n.sym;
-	  goto found_ifc;
-	}
-
-      gcc_unreachable ();
+      gcc_assert (expr->symtree);
+      func_ifc = expr->symtree->n.sym;
+      goto found_ifc;
     }
 
   comp = gfc_get_proc_ptr_comp (expr);
diff --git a/gcc/sched-deps.c b/gcc/sched-deps.c
index 5814204..62aa47a 100644
--- a/gcc/sched-deps.c
+++ b/gcc/sched-deps.c
@@ -3816,7 +3816,6 @@ sched_analyze (class deps_desc *deps, rtx_insn *head, rtx_insn *tail)
 
   for (insn = head;; insn = NEXT_INSN (insn))
     {
-
       if (INSN_P (insn))
 	{
 	  /* And initialize deps_lists.  */
@@ -3836,7 +3835,6 @@ sched_analyze (class deps_desc *deps, rtx_insn *head, rtx_insn *tail)
 	  return;
 	}
     }
-  gcc_unreachable ();
 }
 
 /* Helper for sched_free_deps ().
diff --git a/gcc/sel-sched-ir.c b/gcc/sel-sched-ir.c
index 48965bf..b76a48e 100644
--- a/gcc/sel-sched-ir.c
+++ b/gcc/sel-sched-ir.c
@@ -4918,9 +4918,6 @@ in_same_ebb_p (insn_t insn, insn_t succ)
 
       ptr = bb_next_bb (ptr);
     }
-
-  gcc_unreachable ();
-  return false;
 }
 
 /* Recomputes the reverse topological order for the function and
diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
index 3c253e2..88fd782 100644
--- a/gcc/tree-ssa-alias.c
+++ b/gcc/tree-ssa-alias.c
@@ -1800,9 +1800,6 @@ nonoverlapping_refs_since_match_p (tree match1, tree ref1,
 	  return 1;
 	}
     }
-
-  ++alias_stats.nonoverlapping_refs_since_match_p_must_overlap;
-  return 0;
 }
 
 /* Return TYPE_UID which can be used to match record types we consider
diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 94c7549..cfea0c8 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -7311,20 +7311,14 @@ vectorize_slp_instance_root_stmt (slp_tree node, slp_instance instance)
     {
       if (SLP_TREE_NUMBER_OF_VEC_STMTS (node) == 1)
 	{
-	  gimple *child_stmt;
-	  int j;
-
-	  FOR_EACH_VEC_ELT (SLP_TREE_VEC_STMTS (node), j, child_stmt)
-	    {
-	      tree vect_lhs = gimple_get_lhs (child_stmt);
-	      tree root_lhs = gimple_get_lhs (instance->root_stmts[0]->stmt);
-	      if (!useless_type_conversion_p (TREE_TYPE (root_lhs),
-					      TREE_TYPE (vect_lhs)))
-		vect_lhs = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (root_lhs),
-				   vect_lhs);
-	      rstmt = gimple_build_assign (root_lhs, vect_lhs);
-	      break;
-	    }
+	  gimple *child_stmt = SLP_TREE_VEC_STMTS (node)[0];
+	  tree vect_lhs = gimple_get_lhs (child_stmt);
+	  tree root_lhs = gimple_get_lhs (instance->root_stmts[0]->stmt);
+	  if (!useless_type_conversion_p (TREE_TYPE (root_lhs),
+					  TREE_TYPE (vect_lhs)))
+	    vect_lhs = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (root_lhs),
+			       vect_lhs);
+	  rstmt = gimple_build_assign (root_lhs, vect_lhs);
 	}
       else if (SLP_TREE_NUMBER_OF_VEC_STMTS (node) > 1)
 	{
diff --git a/gcc/tree.c b/gcc/tree.c
index 910fb06..4d91fde 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -11127,7 +11127,6 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
     case TREE_LIST:
       WALK_SUBTREE (TREE_VALUE (*tp));
       WALK_SUBTREE_TAIL (TREE_CHAIN (*tp));
-      break;
 
     case TREE_VEC:
       {
@@ -11206,7 +11205,6 @@ walk_tree_1 (tree *tp, walk_tree_fn func, void *data,
 	  WALK_SUBTREE (OMP_CLAUSE_OPERAND (*tp, i));
 	WALK_SUBTREE_TAIL (OMP_CLAUSE_CHAIN (*tp));
       }
-      break;
 
     case TARGET_EXPR:
       {
diff --git a/gcc/vec-perm-indices.c b/gcc/vec-perm-indices.c
index 31b32ea..9e6b5af 100644
--- a/gcc/vec-perm-indices.c
+++ b/gcc/vec-perm-indices.c
@@ -228,7 +228,6 @@ vec_perm_indices::series_p (unsigned int out_base, unsigned int out_step,
 
       out_base += out_step;
     }
-  return true;
 }
 
 /* Return true if all elements of the permutation vector are in the range