From d21252de6c81ed236d8981d47b9a57dc4f1c6d57 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Wed, 5 Aug 2020 15:05:30 -0400 Subject: c++: cxx_eval_vec_init after zero-initialization [PR96282] In the first testcase below, expand_aggr_init_1 sets up t's default constructor such that the ctor first zero-initializes the entire base b, followed by calling b's default constructor, the latter of which just default-initializes the array member b::m via a VEC_INIT_EXPR. So upon constexpr evaluation of this latter VEC_INIT_EXPR, ctx->ctor is nonempty due to the prior zero-initialization, and we proceed in cxx_eval_vec_init to append new constructor_elts to the end of ctx->ctor without first checking if a matching constructor_elt already exists. This leads to ctx->ctor having two matching constructor_elts for each index. This patch fixes this issue by truncating a zero-initialized array CONSTRUCTOR in cxx_eval_vec_init_1 before we begin appending array elements to it. We propagate its zeroed out state during evaluation by clearing CONSTRUCTOR_NO_CLEARING on each new appended aggregate element. gcc/cp/ChangeLog: PR c++/96282 * constexpr.c (cxx_eval_vec_init_1): Truncate ctx->ctor and then clear CONSTRUCTOR_NO_CLEARING on each appended element initializer if we're initializing a previously zero-initialized array object. gcc/testsuite/ChangeLog: PR c++/96282 * g++.dg/cpp0x/constexpr-array26.C: New test. * g++.dg/cpp0x/constexpr-array27.C: New test. * g++.dg/cpp2a/constexpr-init18.C: New test. Co-authored-by: Jason Merrill --- gcc/cp/constexpr.c | 18 +++++++++++++++++- gcc/testsuite/g++.dg/cpp0x/constexpr-array26.C | 13 +++++++++++++ gcc/testsuite/g++.dg/cpp0x/constexpr-array27.C | 13 +++++++++++++ gcc/testsuite/g++.dg/cpp2a/constexpr-init18.C | 16 ++++++++++++++++ 4 files changed, 59 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-array26.C create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-array27.C create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-init18.C diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index b1c1d24..ab747a5 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -4171,6 +4171,18 @@ cxx_eval_vec_init_1 (const constexpr_ctx *ctx, tree atype, tree init, pre_init = true; } + bool zeroed_out = false; + if (!CONSTRUCTOR_NO_CLEARING (ctx->ctor)) + { + /* We're initializing an array object that had been zero-initialized + earlier. Truncate ctx->ctor, and propagate its zeroed state by + clearing CONSTRUCTOR_NO_CLEARING on each of the aggregate element + initializers we append to it. */ + gcc_checking_assert (initializer_zerop (ctx->ctor)); + zeroed_out = true; + vec_safe_truncate (*p, 0); + } + tree nelts = get_array_or_vector_nelts (ctx, atype, non_constant_p, overflow_p); unsigned HOST_WIDE_INT max = tree_to_uhwi (nelts); @@ -4182,7 +4194,11 @@ cxx_eval_vec_init_1 (const constexpr_ctx *ctx, tree atype, tree init, constexpr_ctx new_ctx; init_subob_ctx (ctx, new_ctx, idx, pre_init ? init : elttype); if (new_ctx.ctor != ctx->ctor) - CONSTRUCTOR_APPEND_ELT (*p, idx, new_ctx.ctor); + { + if (zeroed_out) + CONSTRUCTOR_NO_CLEARING (new_ctx.ctor) = false; + CONSTRUCTOR_APPEND_ELT (*p, idx, new_ctx.ctor); + } if (TREE_CODE (elttype) == ARRAY_TYPE) { /* A multidimensional array; recurse. */ diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-array26.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-array26.C new file mode 100644 index 0000000..274f55a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-array26.C @@ -0,0 +1,13 @@ +// PR c++/96282 +// { dg-do compile { target c++11 } } + +struct e { bool v = true; }; + +template +struct b { e m[N]; }; + +template +struct t : b { constexpr t() : b() {} }; + +constexpr t<1> h1; +constexpr t<42> h2; diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-array27.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-array27.C new file mode 100644 index 0000000..1234cae --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-array27.C @@ -0,0 +1,13 @@ +// PR c++/96282 +// { dg-do compile { target c++11 } } + +struct e { bool v = true; e *p = this; }; + +template +struct b { e m[N][N]; }; + +template +struct t : b { constexpr t() : b() {} }; + +constexpr t<1> h1; +constexpr t<42> h2; diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-init18.C b/gcc/testsuite/g++.dg/cpp2a/constexpr-init18.C new file mode 100644 index 0000000..47ad11f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-init18.C @@ -0,0 +1,16 @@ +// PR c++/96282 +// { dg-do compile { target c++20 } } + +struct e { bool v = true; bool w; }; + +template +struct b { e m[N][N]; }; + +template +struct t : b { constexpr t() : b() {} }; + +constexpr t<1> h1; +static_assert(h1.m[0][0].w == false); + +constexpr t<42> h2; +static_assert(h2.m[17][17].w == false); -- cgit v1.1