Hi!
cxx_eval_switch_expr assumes that SWITCH_EXPR's body is always a
STATEMENT_LIST, but that doesn't have to be the case.
As the testcase shows, if there are any variable declarations in the
switch body, it can be also a BIND_EXPR, which cxx_eval_constant_expression
handles properly, and as bar in the testcase shows, it can be also just
a single statement (as try isn't allowed in constexpr functions, I think
we just want to do what cxx_eval_statement_list would do on such a statement
if it was wrapped into a STATEMENT_LIST - ignore it, as the case NNN: or
default:
is not present.
Bootstrapped/regtested on x86_64-linux and i686-linux? What about older
branches?
2016-09-05 Jakub Jelinek <ja...@redhat.com>
PR c++/77467
* constexpr.c (cxx_eval_switch_expr): Call cxx_eval_constant_expression
instead of cxx_eval_statement_list, for body other than STATEMENT_LIST
or BIND_EXPR don't evaluate the body at all.
* g++.dg/cpp1y/constexpr-77467.C: New test.
--- gcc/cp/constexpr.c.jj 2016-08-30 08:42:06.000000000 +0200
+++ gcc/cp/constexpr.c 2016-09-05 11:34:30.185518395 +0200
@@ -3572,8 +3572,12 @@ cxx_eval_switch_expr (const constexpr_ct
*jump_target = cond;
tree body = TREE_OPERAND (t, 1);
- cxx_eval_statement_list (ctx, body,
- non_constant_p, overflow_p, jump_target);
+ /* If body is a statement other than STATEMENT_LIST or BIND_EXPR,
+ it should be skipped. E.g. switch (a) b = a; */
+ if (TREE_CODE (body) == STATEMENT_LIST
+ || TREE_CODE (body) == BIND_EXPR)
+ cxx_eval_constant_expression (ctx, body, false,
+ non_constant_p, overflow_p, jump_target);
if (breaks (jump_target) || switches (jump_target))
*jump_target = NULL_TREE;
return NULL_TREE;
--- gcc/testsuite/g++.dg/cpp1y/constexpr-77467.C.jj 2016-09-05
11:19:30.593750642 +0200
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-77467.C 2016-09-05
11:37:11.929477518 +0200
@@ -0,0 +1,33 @@
+// 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, "");
Jakub
