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| author | Jason Merrill <jason@redhat.com> | 2020-02-03 11:11:55 -0500 |
|---|---|---|
| committer | Jason Merrill <jason@redhat.com> | 2020-02-03 17:50:36 -0500 |
| commit | 8fda2c274ac66d60c1dfc1349e9efb4e8c2a3580 (patch) | |
| tree | 9c5d0041838e29c8f570733b021348cd3effa683 /gcc/cp/constexpr.c | |
| parent | 19e43cbce353b63a05c3b7c39d83a2e32c9f911f (diff) | |
| download | gcc-8fda2c274ac66d60c1dfc1349e9efb4e8c2a3580.zip gcc-8fda2c274ac66d60c1dfc1349e9efb4e8c2a3580.tar.gz gcc-8fda2c274ac66d60c1dfc1349e9efb4e8c2a3580.tar.bz2 | |
c++: Allow parm of empty class type in constexpr.
Since copying a class object is defined in terms of the copy constructor,
copying an empty class is OK even if it would otherwise not be usable in a
constant expression. Relatedly, using a parameter as an lvalue is no more
problematic than a local variable, and calling a member function uses the
object as an lvalue.
PR c++/91953
* constexpr.c (potential_constant_expression_1) [PARM_DECL]: Allow
empty class type.
[COMPONENT_REF]: A member function reference doesn't use the object
as an rvalue.
Diffstat (limited to 'gcc/cp/constexpr.c')
| -rw-r--r-- | gcc/cp/constexpr.c | 19 |
1 files changed, 15 insertions, 4 deletions
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index 577022e..a39ba41 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -7013,8 +7013,13 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, return true; case PARM_DECL: - if (now) + if (now && want_rval) { + tree type = TREE_TYPE (t); + if (dependent_type_p (type) + || is_really_empty_class (type, /*ignore_vptr*/false)) + /* An empty class has no data to read. */ + return true; if (flags & tf_error) error ("%qE is not a constant expression", t); return false; @@ -7270,10 +7275,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, #endif return RECUR (t, any); - case REALPART_EXPR: - case IMAGPART_EXPR: case COMPONENT_REF: - case BIT_FIELD_REF: case ARROW_EXPR: case OFFSET_REF: /* -- a class member access unless its postfix-expression is @@ -7282,6 +7284,15 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, postfix-expression being a potential constant expression. */ if (type_unknown_p (t)) return true; + if (is_overloaded_fn (t)) + /* In a template, a COMPONENT_REF of a function expresses ob.fn(), + which uses ob as an lvalue. */ + want_rval = false; + gcc_fallthrough (); + + case REALPART_EXPR: + case IMAGPART_EXPR: + case BIT_FIELD_REF: return RECUR (TREE_OPERAND (t, 0), want_rval); case EXPR_PACK_EXPANSION: |