From 077dd9b3f17710da8af6adce816754ddceb57b5a Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Mon, 13 Apr 2020 16:53:02 -0400 Subject: [PATCH] c++: More self-modifying constexpr init [PR94470] In this PR we're incorrectly rejecting a self-modifying constexpr initializer as a consequence of the fix for PR78572. It looks like however that the fix for PR78572 is obsoleted by the fix for PR89336: the testcase from the former PR successfully compiles even with its fix reverted. But then further testing showed that the analogous testcase of PR78572 where the array has an aggregate element type is still problematic (i.e. we ICE) even with the fix for PR78572 applied. The reason is that in cxx_eval_bare_aggregate we attach a constructor_elt of aggregate type always to the end of the new CONSTRUCTOR, but that's not necessarily correct if the CONSTRUCTOR is self-modifying. We should instead be using get_or_insert_ctor_field to insert the constructor_elt in the right place. So this patch reverts the PR78572 fix and makes the appropriate changes to cxx_eval_bare_aggregate. This fixes PR94470, and we now are also able to fully reduce the initializers of 'arr' and 'arr2' in the new test array57.C to constant initializers. gcc/cp/ChangeLog: PR c++/94470 * constexpr.c (get_or_insert_ctor_field): Set default value of parameter 'pos_hint' to -1. (cxx_eval_bare_aggregate): Use get_or_insert_ctor_field instead of assuming the the next index belongs at the end of the new CONSTRUCTOR. (cxx_eval_store_expression): Revert PR c++/78572 fix. gcc/testsuite/ChangeLog: PR c++/94470 * g++.dg/cpp1y/constexpr-nsdmi8.C: New test. * g++.dg/cpp1y/constexpr-nsdmi9.C: New test. * g++.dg/init/array57.C: New test. --- gcc/cp/ChangeLog | 9 +++++++++ gcc/cp/constexpr.c | 19 +++++++------------ gcc/testsuite/ChangeLog | 7 +++++++ gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi8.C | 11 +++++++++++ gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi9.C | 16 ++++++++++++++++ gcc/testsuite/g++.dg/init/array57.C | 16 ++++++++++++++++ 6 files changed, 66 insertions(+), 12 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi8.C create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi9.C create mode 100644 gcc/testsuite/g++.dg/init/array57.C diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog index 9de64c0f1ac..3da61dbcfd9 100644 --- a/gcc/cp/ChangeLog +++ b/gcc/cp/ChangeLog @@ -1,3 +1,12 @@ +2020-04-13 Patrick Palka + + PR c++/94470 + * constexpr.c (get_or_insert_ctor_field): Set default value of parameter + 'pos_hint' to -1. + (cxx_eval_bare_aggregate): Use get_or_insert_ctor_field instead of + assuming the the next index belongs at the end of the new CONSTRUCTOR. + (cxx_eval_store_expression): Revert PR c++/78572 fix. + 2020-04-13 Nathan Sidwell PR c++/94426 lambdas with internal linkage are different to no-linkage diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index 5793430c88d..d8636ddb92f 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -3161,7 +3161,7 @@ find_array_ctor_elt (tree ary, tree dindex, bool insert) for the (integer) index of the matching constructor_elt within CTOR. */ static constructor_elt * -get_or_insert_ctor_field (tree ctor, tree index, int pos_hint) +get_or_insert_ctor_field (tree ctor, tree index, int pos_hint = -1) { /* Check the hint first. */ if (pos_hint >= 0 && (unsigned)pos_hint < CONSTRUCTOR_NELTS (ctor) @@ -3860,14 +3860,15 @@ cxx_eval_bare_aggregate (const constexpr_ctx *ctx, tree t, { /* If we built a new CONSTRUCTOR, attach it now so that other initializers can refer to it. */ - CONSTRUCTOR_APPEND_ELT (*p, index, new_ctx.ctor); - pos_hint = vec_safe_length (*p) - 1; + constructor_elt *cep = get_or_insert_ctor_field (ctx->ctor, index); + cep->value = new_ctx.ctor; + pos_hint = cep - (*p)->begin(); } else if (TREE_CODE (type) == UNION_TYPE) /* Otherwise if we're constructing a non-aggregate union member, set the active union member now so that we can later detect and diagnose if its initializer attempts to activate another member. */ - CONSTRUCTOR_APPEND_ELT (*p, index, NULL_TREE); + get_or_insert_ctor_field (ctx->ctor, index); tree elt = cxx_eval_constant_expression (&new_ctx, value, lval, non_constant_p, overflow_p); @@ -4667,13 +4668,7 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, /* And then find/build up our initializer for the path to the subobject we're initializing. */ tree *valp; - if (object == ctx->object && VAR_P (object) - && DECL_NAME (object) && ctx->call == NULL) - /* The variable we're building up an aggregate initializer for is outside - the constant-expression, so don't evaluate the store. We check - DECL_NAME to handle TARGET_EXPR temporaries, which are fair game. */ - valp = NULL; - else if (DECL_P (object)) + if (DECL_P (object)) valp = ctx->global->values.get (object); else valp = NULL; @@ -4769,7 +4764,7 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, vec_safe_push (indexes, index); constructor_elt *cep - = get_or_insert_ctor_field (*valp, index, /*pos_hint=*/-1); + = get_or_insert_ctor_field (*valp, index); index_pos_hints.safe_push (cep - CONSTRUCTOR_ELTS (*valp)->begin()); if (code == UNION_TYPE) diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index e0d3ea91d57..74a7fa10163 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,10 @@ +2020-04-13 Patrick Palka + + PR c++/94470 + * g++.dg/cpp1y/constexpr-nsdmi8.C: New test. + * g++.dg/cpp1y/constexpr-nsdmi9.C: New test. + * g++.dg/init/array57.C: New test. + 2020-04-13 Iain Sandoe * g++.dg/coroutines/coro-pre-proc.C: Update coroutines builtin diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi8.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi8.C new file mode 100644 index 00000000000..6b77432f61a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi8.C @@ -0,0 +1,11 @@ +// PR c++/94470 +// { dg-do compile { target c++14 } } + +struct X +{ + int b = (c=5); + int c = (b=1); +}; + +constexpr X o = { }; +static_assert(o.b == 1 && o.c == 1, ""); diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi9.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi9.C new file mode 100644 index 00000000000..d51465d8439 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-nsdmi9.C @@ -0,0 +1,16 @@ +// PR c++/94470 +// { dg-do compile { target c++14 } } + +struct Y +{ + int a; +}; + +struct X +{ + Y b = (c={5}); + Y c = (b={1}); +}; + +constexpr X o = { }; +static_assert(o.b.a == 1 && o.c.a == 1, ""); diff --git a/gcc/testsuite/g++.dg/init/array57.C b/gcc/testsuite/g++.dg/init/array57.C new file mode 100644 index 00000000000..2f012b7a231 --- /dev/null +++ b/gcc/testsuite/g++.dg/init/array57.C @@ -0,0 +1,16 @@ +// PR c++/78572 +// { dg-do run { target c++11 } } + +static int arr[10] = { arr[3]=5, arr[7]=3, }; + +struct X { int v; }; +static X arr2[10] = { arr2[3]={5}, arr2[7]={3}, }; + +int +main() +{ + const int expected[10] = {5,3,0,5,0,0,0,3,0,0}; + for (int i = 0; i < 10; i++) + if (arr[i] != expected[i] || arr2[i].v != expected[i]) + __builtin_abort(); +} -- 2.30.2