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| author | Patrick Palka <ppalka@redhat.com> | 2021-09-14 11:22:12 -0400 |
|---|---|---|
| committer | Patrick Palka <ppalka@redhat.com> | 2021-09-14 11:22:12 -0400 |
| commit | de07cff96abd43f6f65dcf333958899c2ec42598 (patch) | |
| tree | 05fbbb6484dff791c6a2a5fd8f82ad60ba12fe00 /gcc/cp/constexpr.c | |
| parent | 818c505188ff5cd8eb048eb0e614c4ef732225bd (diff) | |
| download | gcc-de07cff96abd43f6f65dcf333958899c2ec42598.zip gcc-de07cff96abd43f6f65dcf333958899c2ec42598.tar.gz gcc-de07cff96abd43f6f65dcf333958899c2ec42598.tar.bz2 | |
c++: empty union member activation during constexpr [PR102163]
Here, the union's constructor is defined to activate its empty data
member _M_rest, but during constexpr evaluation of this constructor the
subobject constructor call O::O(&_M_rest, 42) doesn't produce a side
effect that actually activates the member, so the union still appears
uninitialized after its constructor has run. This patch fixes this by
using a dummy MODIFY_EXPR in this situation, whose evaluation ensures
the member gets activated.
PR c++/102163
gcc/cp/ChangeLog:
* constexpr.c (cxx_eval_call_expression): After evaluating a
subobject constructor call for an empty union member, produce a
side effect that makes sure the member gets activated.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-empty17.C: New test.
Diffstat (limited to 'gcc/cp/constexpr.c')
| -rw-r--r-- | gcc/cp/constexpr.c | 34 |
1 files changed, 28 insertions, 6 deletions
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index 0c2498a..d3c075c 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -2787,12 +2787,34 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t, &jump_target); if (DECL_CONSTRUCTOR_P (fun)) - /* This can be null for a subobject constructor call, in - which case what we care about is the initialization - side-effects rather than the value. We could get at the - value by evaluating *this, but we don't bother; there's - no need to put such a call in the hash table. */ - result = lval ? ctx->object : ctx->ctor; + { + /* This can be null for a subobject constructor call, in + which case what we care about is the initialization + side-effects rather than the value. We could get at the + value by evaluating *this, but we don't bother; there's + no need to put such a call in the hash table. */ + result = lval ? ctx->object : ctx->ctor; + + /* If we've just evaluated a subobject constructor call for an + empty union member, it might not have produced a side effect + that actually activated the union member. So produce such a + side effect now to ensure the union appears initialized. */ + if (!result && new_obj + && TREE_CODE (new_obj) == COMPONENT_REF + && TREE_CODE (TREE_TYPE + (TREE_OPERAND (new_obj, 0))) == UNION_TYPE + && is_really_empty_class (TREE_TYPE (new_obj), + /*ignore_vptr*/false)) + { + tree activate = build2 (MODIFY_EXPR, TREE_TYPE (new_obj), + new_obj, + build_constructor (TREE_TYPE (new_obj), + NULL)); + cxx_eval_constant_expression (ctx, activate, lval, + non_constant_p, overflow_p); + ggc_free (activate); + } + } else if (VOID_TYPE_P (TREE_TYPE (res))) result = void_node; else |