[C++ PATCH] PR c++/86678 - constexpr function with non-constant after return.
Jason Merrill
jason@redhat.com
Sat Sep 8 15:58:00 GMT 2018
In this testcase, the call to f() can never be a constant
expression, but that's not a problem because it isn't always
reached by calls to g. We were wrongly rejecting this because
potential_constant_expression_1 lacked the jump tracking that
cxx_eval_constant_expression has. So this patch adds a simpler
version of that tracking.
Tested x86_64-pc-linux-gnu, applying to trunk.
* constexpr.c (potential_constant_expression_1): Add jump_target.
(breaks): Check for BREAK_STMT.
(continues): Check for CONTINUE_STMT.
---
gcc/cp/constexpr.c | 66 +++++++++++++++----
.../g++.dg/cpp1y/constexpr-return4.C | 10 +++
gcc/cp/ChangeLog | 7 ++
3 files changed, 70 insertions(+), 13 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-return4.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 6c2689064f3..68cdd8dc88e 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -3893,6 +3893,7 @@ breaks (tree *jump_target)
return *jump_target
&& ((TREE_CODE (*jump_target) == LABEL_DECL
&& LABEL_DECL_BREAK (*jump_target))
+ || TREE_CODE (*jump_target) == BREAK_STMT
|| TREE_CODE (*jump_target) == EXIT_EXPR);
}
@@ -3900,8 +3901,10 @@ static bool
continues (tree *jump_target)
{
return *jump_target
- && TREE_CODE (*jump_target) == LABEL_DECL
- && LABEL_DECL_CONTINUE (*jump_target);
+ && ((TREE_CODE (*jump_target) == LABEL_DECL
+ && LABEL_DECL_CONTINUE (*jump_target))
+ || TREE_CODE (*jump_target) == CONTINUE_STMT);
+
}
static bool
@@ -4123,7 +4126,7 @@ static tree
cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
bool lval,
bool *non_constant_p, bool *overflow_p,
- tree *jump_target)
+ tree *jump_target /* = NULL */)
{
constexpr_ctx new_ctx;
tree r = t;
@@ -4149,7 +4152,7 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
return NULL_TREE;
}
}
- if (t == error_mark_node)
+ if (error_operand_p (t))
{
*non_constant_p = true;
return t;
@@ -5398,10 +5401,10 @@ check_automatic_or_tls (tree ref)
static bool
potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
- tsubst_flags_t flags)
+ tsubst_flags_t flags, tree *jump_target)
{
#define RECUR(T,RV) \
- potential_constant_expression_1 ((T), (RV), strict, now, flags)
+ potential_constant_expression_1 ((T), (RV), strict, now, flags, jump_target)
enum { any = false, rval = true };
int i;
@@ -5412,6 +5415,14 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
if (t == NULL_TREE)
return true;
location_t loc = cp_expr_loc_or_loc (t, input_location);
+
+ if (*jump_target)
+ /* If we are jumping, ignore everything. This is simpler than the
+ cxx_eval_constant_expression handling because we only need to be
+ conservatively correct, and we don't necessarily have a constant value
+ available, so we don't bother with switch tracking. */
+ return true;
+
if (TREE_THIS_VOLATILE (t) && !DECL_P (t))
{
if (flags & tf_error)
@@ -5449,13 +5460,21 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
case USING_DECL:
case USING_STMT:
case PLACEHOLDER_EXPR:
- case BREAK_STMT:
- case CONTINUE_STMT:
case REQUIRES_EXPR:
case STATIC_ASSERT:
case DEBUG_BEGIN_STMT:
return true;
+ case RETURN_EXPR:
+ if (!RECUR (TREE_OPERAND (t, 0), any))
+ return false;
+ /* FALLTHROUGH */
+
+ case BREAK_STMT:
+ case CONTINUE_STMT:
+ *jump_target = t;
+ return true;
+
case PARM_DECL:
if (now)
{
@@ -5544,7 +5563,8 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
constexpr substitution might not use the value. */
bool sub_now = false;
if (!potential_constant_expression_1 (x, rval, strict,
- sub_now, flags))
+ sub_now, flags,
+ jump_target))
return false;
i = 1;
}
@@ -5578,7 +5598,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
substitution might not use the value of the argument. */
bool sub_now = false;
if (!potential_constant_expression_1 (x, rv, strict,
- sub_now, flags))
+ sub_now, flags, jump_target))
return false;
}
return true;
@@ -5753,6 +5773,8 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
return false;
if (!RECUR (DO_BODY (t), any))
return false;
+ if (breaks (jump_target) || continues (jump_target))
+ *jump_target = NULL_TREE;
return true;
case FOR_STMT:
@@ -5764,6 +5786,8 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
return false;
if (!RECUR (FOR_BODY (t), any))
return false;
+ if (breaks (jump_target) || continues (jump_target))
+ *jump_target = NULL_TREE;
return true;
case RANGE_FOR_STMT:
@@ -5773,6 +5797,8 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
return false;
if (!RECUR (RANGE_FOR_BODY (t), any))
return false;
+ if (breaks (jump_target) || continues (jump_target))
+ *jump_target = NULL_TREE;
return true;
case WHILE_STMT:
@@ -5780,6 +5806,8 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
return false;
if (!RECUR (WHILE_BODY (t), any))
return false;
+ if (breaks (jump_target) || continues (jump_target))
+ *jump_target = NULL_TREE;
return true;
case SWITCH_STMT:
@@ -5963,7 +5991,6 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
case PAREN_EXPR:
case NON_DEPENDENT_EXPR:
/* For convenience. */
- case RETURN_EXPR:
case LOOP_EXPR:
case EXIT_EXPR:
return RECUR (TREE_OPERAND (t, 0), want_rval);
@@ -6173,7 +6200,8 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
return RECUR (TREE_OPERAND (t, 1), want_rval);
for (i = 1; i < 3; ++i)
if (potential_constant_expression_1 (TREE_OPERAND (t, i),
- want_rval, strict, now, tf_none))
+ want_rval, strict, now,
+ tf_none, jump_target))
return true;
if (flags & tf_error)
error_at (loc, "expression %qE is not a constant expression", t);
@@ -6204,7 +6232,10 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
tree *target = &TREE_OPERAND (t, 0);
/* Gotos representing break and continue are OK. */
if (breaks (target) || continues (target))
- return true;
+ {
+ *jump_target = *target;
+ return true;
+ }
if (flags & tf_error)
error_at (loc, "%<goto%> is not a constant expression");
return false;
@@ -6224,6 +6255,15 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
#undef RECUR
}
+bool
+potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
+ tsubst_flags_t flags)
+{
+ tree target = NULL_TREE;
+ return potential_constant_expression_1 (t, want_rval, strict, now,
+ flags, &target);
+}
+
/* The main entry point to the above. */
bool
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-return4.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-return4.C
new file mode 100644
index 00000000000..8f29628148f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-return4.C
@@ -0,0 +1,10 @@
+// PR c++/86678
+// { dg-do compile { target c++14 } }
+
+constexpr bool always_true() { return true; }
+int f() { return 1; }
+constexpr int g() {
+ if (always_true())
+ return 0;
+ return f();
+}
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 70c462cad78..87a575e6034 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,10 @@
+2018-09-08 Jason Merrill <jason@redhat.com>
+
+ PR c++/86678 - constexpr function with non-constant after return.
+ * constexpr.c (potential_constant_expression_1): Add jump_target.
+ (breaks): Check for BREAK_STMT.
+ (continues): Check for CONTINUE_STMT.
+
2018-09-07 Marek Polacek <polacek@redhat.com>
PR c++/87152 - range-based for loops with initializer broken in templates.
base-commit: 2a4787da69071b5d5bc178795accca264073b7e4
--
2.17.1
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