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author | Marek Polacek <polacek@redhat.com> | 2022-05-25 18:11:31 -0400 |
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committer | Marek Polacek <polacek@redhat.com> | 2022-07-01 12:07:34 -0400 |
commit | ecd11acacd6be57af930fa617d7c31ecb40e7f74 (patch) | |
tree | 78da6f3fa4cbeec13ab2abf2b93d7a8c98015863 /gcc | |
parent | 9a668532fb19e7c57aa595a26ce3f0d95f9cbb1b (diff) | |
download | gcc-ecd11acacd6be57af930fa617d7c31ecb40e7f74.zip gcc-ecd11acacd6be57af930fa617d7c31ecb40e7f74.tar.gz gcc-ecd11acacd6be57af930fa617d7c31ecb40e7f74.tar.bz2 |
c++: fix broken copy elision with nested TARGET_EXPRs [PR105550]
In this problem, we are failing to properly perform copy elision with
a conditional operator, so this:
constexpr A a = true ? A{} : A{};
fails with:
error: 'A{((const A*)(&<anonymous>))}' is not a constant expression
The whole initializer is
TARGET_EXPR <D.2395, 1 ? TARGET_EXPR <D.2393, {.p=(const struct A *) &<PLACEHOLDER_EXPR struct A>}> : TARGET_EXPR <D.2394, {.p=(const struct A *) &<PLACEHOLDER_EXPR struct A>}>>
where the outermost TARGET_EXPR is elided, but not the nested ones.
Then we end up replacing the PLACEHOLDER_EXPRs with the temporaries the
TARGET_EXPRs represent, which is precisely what should *not* happen with
copy elision.
I've tried the approach of tweaking ctx->object, but I ran into gazillion
problems with that. I thought that I would let cxx_eval_constant_expression
/TARGET_EXPR create a new object only when ctx->object was null, then
adjust setting of ctx->object in places like cxx_bind_parameters_in_call
and cxx_eval_component_reference but that failed completely. Sometimes
ctx->object has to be reset, sometimes it cannot be reset, 'this' needed
special handling, etc. I gave up.
Instead, this patch strips TARGET_EXPRs from the operands of ?: like
we do in various other places in constexpr.c.
PR c++/105550
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_conditional_expression): Strip TARGET_EXPRs.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/nsdmi-aggr16.C: Remove FIXME.
* g++.dg/cpp1y/nsdmi-aggr17.C: Remove FIXME.
* g++.dg/cpp0x/constexpr-elision1.C: New test.
* g++.dg/cpp1y/constexpr-elision1.C: New test.
Diffstat (limited to 'gcc')
-rw-r--r-- | gcc/cp/constexpr.cc | 7 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/cpp0x/constexpr-elision1.C | 16 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/cpp1y/constexpr-elision1.C | 53 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C | 5 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C | 5 |
5 files changed, 80 insertions, 6 deletions
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index 0dc94d9..5f7fc6f 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -3507,6 +3507,13 @@ cxx_eval_conditional_expression (const constexpr_ctx *ctx, tree t, val = TREE_OPERAND (t, 1); if (TREE_CODE (t) == IF_STMT && !val) val = void_node; + /* A TARGET_EXPR may be nested inside another TARGET_EXPR, but still + serve as the initializer for the same object as the outer TARGET_EXPR, + as in + A a = true ? A{} : A{}; + so strip the inner TARGET_EXPR so we don't materialize a temporary. */ + if (TREE_CODE (val) == TARGET_EXPR) + val = TARGET_EXPR_INITIAL (val); return cxx_eval_constant_expression (ctx, val, lval, non_constant_p, overflow_p, jump_target); } diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-elision1.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-elision1.C new file mode 100644 index 0000000..9e7b9ec --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-elision1.C @@ -0,0 +1,16 @@ +// PR c++/105550 +// { dg-do compile { target c++11 } } + +template <typename, typename> struct pair { + constexpr pair(int, int) {} +}; +template <typename _Tp, typename _Compare> +pair<const _Tp &, const _Tp &> minmax(const _Tp &__a, const _Tp &__b, + _Compare) { + return 0 ? pair<const _Tp &, const _Tp &>(__b, __a) + : pair<const _Tp &, const _Tp &>(__a, __b); +} +typedef int value_type; +typedef int compare_type; +template pair<const value_type &, const value_type &> +minmax(const value_type &, const value_type &, compare_type); diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-elision1.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-elision1.C new file mode 100644 index 0000000..b225ae2 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-elision1.C @@ -0,0 +1,53 @@ +// PR c++/105550 +// { dg-do compile { target c++14 } } + +struct A { + const A *p = this; +}; + +struct B { + const B *p = this; + constexpr operator A() const { return {}; } +}; + +constexpr A +bar (A) +{ + return {}; +} + +constexpr A baz() { return {}; } + +struct E { + A a1 = true ? A{} : A{}; + A a2 = true ? A{} : B{}; + A a3 = false ? A{} : B{}; + A a4 = false ? B{} : B{}; + A a5 = A{}; + A a6 = B{}; + A a7 = false ? B{} : (true ? A{} : A{}); + A a8 = false ? (true ? A{} : B{}) : (true ? A{} : A{}); + A a9 = (A{}); + A a10 = (true, A{}); + A a11 = bar (A{}); + A a12 = baz (); + A a13 = (A{}, A{}); +}; + +constexpr E e{}; + +constexpr A a1 = true ? A{} : A{}; +constexpr A a2 = true ? A{} : B{}; +constexpr A a3 = false ? A{} : B{}; +constexpr A a4 = false ? B{} : B{}; +constexpr A a5 = A{}; +constexpr A a6 = B{}; +constexpr A a7 = false ? B{} : (true ? A{} : A{}); +constexpr A a8 = false ? (true ? A{} : B{}) : (true ? A{} : A{}); +constexpr A a9 = (A{}); +constexpr A a10 = (true, A{}); +constexpr A a11 = bar (A{}); +//static_assert(a10.p == &a10, ""); // bug, 105619 +constexpr A a12 = baz (); +//static_assert(a11.p == &a11, ""); // bug, 105619 +constexpr A a13 = (A{}, A{}); diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C index dc6492c..5e66bdd 100644 --- a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C +++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C @@ -40,9 +40,8 @@ struct E { A d = true ? (false ? A{} : A{}) : (false ? A{} : A{}); }; -// FIXME: When fixing this, also fix nsdmi-aggr17.C. -constexpr E e; // { dg-bogus "" "PR105550" { xfail *-*-* } } -SA (e.a.p == &e.a); // { dg-bogus "" "PR105550" { xfail *-*-* } } +constexpr E e; +SA (e.a.p == &e.a); E e1 = { }; diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C index fc27a2c..ca9637b 100644 --- a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C +++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C @@ -56,9 +56,8 @@ struct F { A a = true ? A{x} : A{x}; }; -// FIXME: Doesn't work due to PR105550. -//constexpr F f; -//SA (f.a.p == &f.a); +constexpr F f; +SA (f.a.p == &f.a); SA (e.x == 42); F f2 = { }; F f3 = { 42 }; |