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c++: Don't form a templated TARGET_EXPR in finish_compound_literal

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The atom_cache in normalize_atom relies on the assumption that two
equivalent (templated) trees (in the sense of cp_tree_equal) must use
the same template parameters (according to find_template_parameters).

This assumption unfortunately doesn't always hold for TARGET_EXPRs,
because cp_tree_equal ignores an artificial target of a TARGET_EXPR, but
find_template_parameters walks this target (and its DECL_CONTEXT).

Hence two TARGET_EXPRs built by force_target_expr with the same
initializer and under different settings of current_function_decl will
compare equal according to cp_tree_equal, but find_template_parameters
may return a different set of template parameters for them.  This breaks
the below testcase because during normalization we build two such
TARGET_EXPRs (one under current_function_decl=f and another under =g),
and then share the same ATOMIC_CONSTR for the two corresponding atoms,
leading to a crash during satisfaction of g's associated constraints.

This patch works around this issue by removing the source of these
templated TARGET_EXPRs.  The relevant call to get_target_expr_sfinae was
added in r9-6043, and it seems it's no longer necessary (according to
https://gcc.gnu.org/pipermail/gcc-patches/2019-February/517323.html, the
call was added in order to avoid regressing on initlist109.C at the time).

gcc/cp/ChangeLog:

	* semantics.c (finish_compound_literal): Don't wrap the original
	compound literal in a TARGET_EXPR when inside a template.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-decltype3.C: New test.
This commit is contained in:
Patrick Palka 2020-11-12 19:07:40 -05:00
parent 93fc477468
commit de6f64f955
2 changed files with 16 additions and 6 deletions
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7
gcc/cp/semantics.c
View file

@ -3006,12 +3006,7 @@ finish_compound_literal (tree type, tree compound_literal,
/* If we're in a template, return the original compound literal. */
if (orig_cl)
{
if (!VECTOR_TYPE_P (type))
return get_target_expr_sfinae (orig_cl, complain);
else
return orig_cl;
}
return orig_cl;
if (TREE_CODE (compound_literal) == CONSTRUCTOR)
{

15
gcc/testsuite/g++.dg/cpp2a/concepts-decltype3.C Normal file
View file

@ -0,0 +1,15 @@
// { dg-do compile { target c++20 } }
template <class T> concept C = requires(T t) { t; };
template <class T> using A = decltype((T{}, int{}));
template <class T> concept D = C<A<T>>;
template <class T, class U> void f() requires D<T>;
template <class T> void g() requires D<T>;
void h() {
f<int, int>();
g<int>();
}