re PR c++/77467 (Segmentation fault with switch statement in constexpr function)

	PR c++/77467
	* constexpr.c (enum constexpr_switch_state): New.
	(struct constexpr_ctx): Add css_state field.
	(label_matches): Add CTX and STMT arguments, remove I and
	DEFAULT_LABEL.  For CASE_LABEL_EXPR assert ctx->css_state != NULL,
	handle default labels according to css_state.
	(cxx_eval_statement_list): Remove statement skipping, label_matches
	and default_label handling code.
	(cxx_eval_loop_expr): Exit after first iteration even if
	switches (jump_target).
	(cxx_eval_switch_expr): Set up css_state field in ctx, if default
	label has been seen in the body, but no cases matched, evaluate
	the body second time.
	(cxx_eval_constant_expression): Handle stmt skipping and label_matches
	here.  Handle PREDICT_EXPR.  For MODIFY_EXPR or INIT_EXPR, assert
	statement is not skipped.  For COND_EXPR during skipping, don't
	evaluate condition, just the then block and if still skipping at the
	end also the else block.
	(cxx_eval_outermost_constant_expr): Adjust constexpr_ctx initializer.
	(is_sub_constant_expr): Likewise.

	* g++.dg/cpp1y/constexpr-77467.C: New test.

From-SVN: r240591

gcc/cp/ChangeLog

+2016-09-28  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/77467
+	* constexpr.c (enum constexpr_switch_state): New.
+	(struct constexpr_ctx): Add css_state field.
+	(label_matches): Add CTX and STMT arguments, remove I and
+	DEFAULT_LABEL.  For CASE_LABEL_EXPR assert ctx->css_state != NULL,
+	handle default labels according to css_state.
+	(cxx_eval_statement_list): Remove statement skipping, label_matches
+	and default_label handling code.
+	(cxx_eval_loop_expr): Exit after first iteration even if
+	switches (jump_target).
+	(cxx_eval_switch_expr): Set up css_state field in ctx, if default
+	label has been seen in the body, but no cases matched, evaluate
+	the body second time.
+	(cxx_eval_constant_expression): Handle stmt skipping and label_matches
+	here.  Handle PREDICT_EXPR.  For MODIFY_EXPR or INIT_EXPR, assert
+	statement is not skipped.  For COND_EXPR during skipping, don't
+	evaluate condition, just the then block and if still skipping at the
+	end also the else block.
+	(cxx_eval_outermost_constant_expr): Adjust constexpr_ctx initializer.
+	(is_sub_constant_expr): Likewise.
+
 2016-09-27  Jakub Jelinek  <jakub@redhat.com>
 
 	Implement P0018R3, C++17 lambda capture of *this by value as [=,*this]

gcc/cp/constexpr.c

@@ -900,6 +900,18 @@ struct constexpr_call_hasher : ggc_ptr_hash<constexpr_call>
   static bool equal (constexpr_call *, constexpr_call *);
 };
 
+enum constexpr_switch_state {
+  /* Used when processing a switch for the first time by cxx_eval_switch_expr
+     and default: label for that switch has not been seen yet.  */
+  css_default_not_seen,
+  /* Used when processing a switch for the first time by cxx_eval_switch_expr
+     and default: label for that switch has been seen already.  */
+  css_default_seen,
+  /* Used when processing a switch for the second time by
+     cxx_eval_switch_expr, where default: label should match.  */
+  css_default_processing
+};
+
 /* The constexpr expansion context.  CALL is the current function
    expansion, CTOR is the current aggregate initializer, OBJECT is the
    object being initialized by CTOR, either a VAR_DECL or a _REF.  VALUES
@@ -919,6 +931,8 @@ struct constexpr_ctx {
   tree ctor;
   /* The object we're building the CONSTRUCTOR for.  */
   tree object;
+  /* If inside SWITCH_EXPR.  */
+  constexpr_switch_state *css_state;
   /* Whether we should error on a non-constant expression or fail quietly.  */
   bool quiet;
   /* Whether we are strictly conforming to constant expression rules or
@@ -3484,14 +3498,12 @@ switches (tree *jump_target)
 }
 
 /* Subroutine of cxx_eval_statement_list.  Determine whether the statement
-   at I matches *jump_target.  If we're looking for a case label and we see
-   the default label, copy I into DEFAULT_LABEL.  */
+   STMT matches *jump_target.  If we're looking for a case label and we see
+   the default label, note it in ctx->css_state.  */
 
 static bool
-label_matches (tree *jump_target, tree_stmt_iterator i,
-	       tree_stmt_iterator& default_label)
+label_matches (const constexpr_ctx *ctx, tree *jump_target, tree stmt)
 {
-  tree stmt = tsi_stmt (i);
   switch (TREE_CODE (*jump_target))
     {
     case LABEL_DECL:
@@ -3503,8 +3515,18 @@ label_matches (tree *jump_target, tree_stmt_iterator i,
     case INTEGER_CST:
       if (TREE_CODE (stmt) == CASE_LABEL_EXPR)
 	{
+	  gcc_assert (ctx->css_state != NULL);
 	  if (!CASE_LOW (stmt))
-	    default_label = i;
+	    {
+	      /* default: should appear just once in a SWITCH_EXPR
+		 body (excluding nested SWITCH_EXPR).  */
+	      gcc_assert (*ctx->css_state != css_default_seen);
+	      /* When evaluating SWITCH_EXPR body for the second time,
+		 return true for the default: label.  */
+	      if (*ctx->css_state == css_default_processing)
+		return true;
+	      *ctx->css_state = css_default_seen;
+	    }
 	  else if (CASE_HIGH (stmt))
 	    {
 	      if (tree_int_cst_le (CASE_LOW (stmt), *jump_target)
@@ -3531,7 +3553,6 @@ cxx_eval_statement_list (const constexpr_ctx *ctx, tree t,
 			 tree *jump_target)
 {
   tree_stmt_iterator i;
-  tree_stmt_iterator default_label = tree_stmt_iterator();
   tree local_target;
   /* In a statement-expression we want to return the last value.  */
   tree r = NULL_TREE;
@@ -3542,18 +3563,7 @@ cxx_eval_statement_list (const constexpr_ctx *ctx, tree t,
     }
   for (i = tsi_start (t); !tsi_end_p (i); tsi_next (&i))
     {
-    reenter:
       tree stmt = tsi_stmt (i);
-      if (*jump_target)
-	{
-	  if (TREE_CODE (stmt) == STATEMENT_LIST)
-	    /* The label we want might be inside.  */;
-	  else if (label_matches (jump_target, i, default_label))
-	    /* Found it.  */
-	    *jump_target = NULL_TREE;
-	  else
-	    continue;
-	}
       r = cxx_eval_constant_expression (ctx, stmt, false,
 					non_constant_p, overflow_p,
 					jump_target);
@@ -3562,12 +3572,6 @@ cxx_eval_statement_list (const constexpr_ctx *ctx, tree t,
       if (returns (jump_target) || breaks (jump_target))
 	break;
     }
-  if (switches (jump_target) && !tsi_end_p (default_label))
-    {
-      i = default_label;
-      *jump_target = NULL_TREE;
-      goto reenter;
-    }
   return r;
 }
 
@@ -3606,7 +3610,10 @@ cxx_eval_loop_expr (const constexpr_ctx *ctx, tree t,
 	  break;
 	}
     }
-  while (!returns (jump_target) && !breaks (jump_target) && !*non_constant_p);
+  while (!returns (jump_target)
+	 && !breaks (jump_target)
+	 && !switches (jump_target)
+	 && !*non_constant_p);
 
   if (breaks (jump_target))
     *jump_target = NULL_TREE;
@@ -3629,8 +3636,20 @@ cxx_eval_switch_expr (const constexpr_ctx *ctx, tree t,
   *jump_target = cond;
 
   tree body = TREE_OPERAND (t, 1);
-  cxx_eval_statement_list (ctx, body,
-			   non_constant_p, overflow_p, jump_target);
+  constexpr_ctx new_ctx = *ctx;
+  constexpr_switch_state css = css_default_not_seen;
+  new_ctx.css_state = &css;
+  cxx_eval_constant_expression (&new_ctx, body, false,
+				non_constant_p, overflow_p, jump_target);
+  if (switches (jump_target) && css == css_default_seen)
+    {
+      /* If the SWITCH_EXPR body has default: label, process it once again,
+	 this time instructing label_matches to return true for default:
+	 label on switches (jump_target).  */
+      css = css_default_processing;
+      cxx_eval_constant_expression (&new_ctx, body, false,
+				    non_constant_p, overflow_p, jump_target);
+    }
   if (breaks (jump_target) || switches (jump_target))
     *jump_target = NULL_TREE;
   return NULL_TREE;
@@ -3650,6 +3669,27 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
   constexpr_ctx new_ctx;
   tree r = t;
 
+  if (jump_target && *jump_target)
+    {
+      /* If we are jumping, ignore all statements/expressions except those
+	 that could have LABEL_EXPR or CASE_LABEL_EXPR in their bodies.  */
+      switch (TREE_CODE (t))
+	{
+	case BIND_EXPR:
+	case STATEMENT_LIST:
+	case LOOP_EXPR:
+	case COND_EXPR:
+	  break;
+	case LABEL_EXPR:
+	case CASE_LABEL_EXPR:
+	  if (label_matches (ctx, jump_target, t))
+	    /* Found it.  */
+	    *jump_target = NULL_TREE;
+	  return NULL_TREE;
+	default:
+	  return NULL_TREE;
+	}
+    }
   if (t == error_mark_node)
     {
       *non_constant_p = true;
@@ -3730,6 +3770,7 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
     case LABEL_DECL:
     case LABEL_EXPR:
     case CASE_LABEL_EXPR:
+    case PREDICT_EXPR:
       return t;
 
     case PARM_DECL:
@@ -3835,6 +3876,7 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
 
     case INIT_EXPR:
     case MODIFY_EXPR:
+      gcc_assert (jump_target == NULL || *jump_target == NULL_TREE);
       r = cxx_eval_store_expression (ctx, t, lval,
 				     non_constant_p, overflow_p);
       break;
@@ -4065,6 +4107,22 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
       break;
 
     case COND_EXPR:
+      if (jump_target && *jump_target)
+	{
+	  /* When jumping to a label, the label might be either in the
+	     then or else blocks, so process then block first in skipping
+	     mode first, and if we are still in the skipping mode at its end,
+	     process the else block too.  */
+	  r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 1),
+					    lval, non_constant_p, overflow_p,
+					    jump_target);
+	  if (*jump_target)
+	    r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 2),
+					      lval, non_constant_p, overflow_p,
+					      jump_target);
+	  break;
+	}
+      /* FALLTHRU */
     case VEC_COND_EXPR:
       r = cxx_eval_conditional_expression (ctx, t, lval,
 					   non_constant_p, overflow_p,
@@ -4340,7 +4398,7 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
   bool overflow_p = false;
   hash_map<tree,tree> map;
 
-  constexpr_ctx ctx = { NULL, &map, NULL, NULL, NULL,
+  constexpr_ctx ctx = { NULL, &map, NULL, NULL, NULL, NULL,
 			allow_non_constant, strict };
 
   tree type = initialized_type (t);
@@ -4460,7 +4518,7 @@ is_sub_constant_expr (tree t)
   bool overflow_p = false;
   hash_map <tree, tree> map;
 
-  constexpr_ctx ctx = { NULL, &map, NULL, NULL, NULL, true, true };
+  constexpr_ctx ctx = { NULL, &map, NULL, NULL, NULL, NULL, true, true };
 
   cxx_eval_constant_expression (&ctx, t, false, &non_constant_p,
 				&overflow_p);

gcc/testsuite/ChangeLog

+2016-09-28  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/77467
+	* g++.dg/cpp1y/constexpr-77467.C: New test.
+
 2016-09-28  Martin Sebor  <msebor@redhat.com>
 
 	PR c/77762

gcc/testsuite/g++.dg/cpp1y/constexpr-77467.C

+// PR c++/77467
+// { dg-do compile { target c++14 } }
+
+constexpr int
+foo (const int x, const unsigned n) noexcept
+{
+  switch (n)
+    {
+    case 0:
+      return 1;
+    case 1:
+      return x;
+    default:
+      const auto m = (n >> 1);
+      const auto y = foo (x, m);
+      return ((m << 1) == n) ? y * y : x * y * y;
+    }
+}
+
+static_assert (foo (3, 2) == 9, "");
+static_assert (foo (2, 3) == 8, "");
+
+constexpr int
+bar (int x)
+{
+  int a = x;
+  switch (x)
+    a = x + 1;
+  return a;
+}
+
+static_assert (bar (0) == 0, "");
+static_assert (bar (1) == 1, "");
+
+constexpr int
+baz (const int x, int y) noexcept
+{
+  switch (x)
+    {
+    case 0:
+      return 1;
+    case 1:
+      return x;
+    case 2:
+      if ((y += 2) == 0)
+	{
+	case 3:
+	  y += 4;
+	  break;
+	}
+      else
+	{
+	case 4:
+	  y += 8;
+	  break;
+	}
+      break;
+    case 5:
+      for (y = 0; y < 3; y++)
+	{
+	case 7:
+	  if (y == -4)
+	    y += 3;
+	  if (y == -3)
+	    continue;
+	  if (y == -2)
+	    {
+	      y += 18;
+	      break;
+	    }
+	  if (y == 2)
+	    {
+	    case 6:
+	      y += 12;
+	    default:
+	      y++;
+	      break;
+	    }
+	}
+      break;
+    case -1:
+    case -2:
+      switch (y)
+	{
+	case 19:
+	  y += 2;
+	  break;
+	case 20:
+	  y += 3;
+	  if (x == 2)
+	    case 21:;
+	  y += 2;
+	  if (x == 3)
+	    default:;
+	  y += 4;
+	  break;
+	}
+      return x + y + 1;
+    }
+  return x + y;
+}
+
+static_assert (baz (0, 7) == 1, "");
+static_assert (baz (1, 7) == 1, "");
+static_assert (baz (2, -2) == 6, "");
+static_assert (baz (2, 0) == 12, "");
+static_assert (baz (3, 1) == 8, "");
+static_assert (baz (4, 2) == 14, "");
+static_assert (baz (5, -20) == 20, "");
+static_assert (baz (6, 5) == 24, "");
+static_assert (baz (7, -5) == 22, "");
+static_assert (baz (7, -4) == 22, "");
+static_assert (baz (7, -3) == 23, "");
+static_assert (baz (7, -2) == 23, "");
+static_assert (baz (7, -1) == 22, "");
+static_assert (baz (7, 0) == 22, "");
+static_assert (baz (7, 2) == 22, "");
+static_assert (baz (7, 6) == 14, "");
+static_assert (baz (8, 9) == 18, "");
+static_assert (baz (8, -2) == 7, "");
+static_assert (baz (-1, 19) == 21, "");
+static_assert (baz (-1, 20) == 29, "");
+static_assert (baz (-1, 21) == 27, "");
+static_assert (baz (-1, 5) == 9, "");
+static_assert (baz (-2, 19) == 20, "");
+static_assert (baz (-2, 20) == 28, "");
+static_assert (baz (-2, 21) == 26, "");
+static_assert (baz (-2, 5) == 8, "");