https://gcc.gnu.org/g:7543dd4654ae17ff44240b037e2a5ef14aca292d
commit r17-1271-g7543dd4654ae17ff44240b037e2a5ef14aca292d Author: Marek Polacek <[email protected]> Date: Wed May 27 13:23:49 2026 -0400 c++: reference tparm refers to temporary object [PR107124] [temp.arg.nontype] tells us that a temporary object is not an acceptable template-argument when the corresponding template parameter has reference type. So template<const int& CRI> struct B { }; B<1> b; is ill-formed. In the test below we have a tparm `const int &I` and we are trying to deduce `I` from `A<0>`. Since a temporary would be required for the template argument, this should be a deduction failure. PR c++/107124 gcc/cp/ChangeLog: * cp-tree.h: Adjust comments to mention maybe_build_nontype_implicit_conv instead of maybe_convert_nontype_argument. * pt.cc (maybe_convert_nontype_argument): Rename to... (maybe_build_nontype_implicit_conv): ...this. (convert_nontype_argument_maybe_dependent): New, factored out of... (convert_template_argument): ...here. (unify) <case TEMPLATE_PARM_INDEX>: Call convert_nontype_argument_maybe_dependent and return unify_invalid if it failed. Don't call strip_typedefs_expr. gcc/testsuite/ChangeLog: * g++.dg/template/deduce11.C: New test. * g++.dg/template/deduce12.C: New test. Reviewed-by: Jason Merrill <[email protected]> Diff: --- gcc/cp/cp-tree.h | 4 +-- gcc/cp/pt.cc | 58 ++++++++++++++++++++------------ gcc/testsuite/g++.dg/template/deduce11.C | 15 +++++++++ gcc/testsuite/g++.dg/template/deduce12.C | 12 +++++++ 4 files changed, 65 insertions(+), 24 deletions(-) diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index 65f112714d14..bf477a67a349 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -5138,7 +5138,7 @@ get_vec_init_expr (tree t) (TREE_LANG_FLAG_0 (IMPLICIT_CONV_EXPR_CHECK (NODE))) /* True if NODE represents a dependent conversion of a non-type template - argument. Set by maybe_convert_nontype_argument. */ + argument. Set by maybe_build_nontype_implicit_conv. */ #define IMPLICIT_CONV_EXPR_NONTYPE_ARG(NODE) \ (TREE_LANG_FLAG_1 (IMPLICIT_CONV_EXPR_CHECK (NODE))) @@ -5148,7 +5148,7 @@ get_vec_init_expr (tree t) (TREE_LANG_FLAG_2 (IMPLICIT_CONV_EXPR_CHECK (NODE))) /* True if NODE represents a conversion forced to be represented in - maybe_convert_nontype_argument, i.e. for an alias template. */ + maybe_build_nontype_implicit_conv, i.e. for an alias template. */ #define IMPLICIT_CONV_EXPR_FORCED(NODE) \ (TREE_LANG_FLAG_3 (IMPLICIT_CONV_EXPR_CHECK (NODE))) diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index b334882de818..4683b57f34b6 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -8740,7 +8740,7 @@ is_compatible_template_arg (tree parm, tree arg, tree args) conversion for the benefit of cp_tree_equal. */ static tree -maybe_convert_nontype_argument (tree type, tree arg, bool force) +maybe_build_nontype_implicit_conv (tree type, tree arg, bool force) { /* Auto parms get no conversion. */ if (type_uses_auto (type)) @@ -8780,6 +8780,33 @@ dependent_implicit_conv_p (tree type, tree expr, bool forced) && value_dependent_expression_p (expr))); } +/* Convert the non-type template parameter ARG to the indicated TYPE. + If one of them is dependent, create an appropriate conversion. + FORCE_CONV is true in a forced context (i.e. alias or concept). */ + +static tree +convert_nontype_argument_maybe_dependent (tree type, tree arg, + bool force_conv, + tsubst_flags_t complain) +{ + if (dependent_implicit_conv_p (type, arg, force_conv)) + { + tree val = canonicalize_expr_argument (arg, complain); + return maybe_build_nontype_implicit_conv (type, val, force_conv); + } + + /* We used to call digest_init here. However, digest_init will report + errors, which we don't want when complain is zero. More importantly, + digest_init will try too hard to convert things: for example, + `0' should not be converted to pointer type at this point according to + the standard. Accepting this is not merely an extension, since + deciding whether or not these conversions can occur is part of + determining which function template to call, or whether a given + explicit argument specification is valid. */ + return convert_nontype_argument (type, convert_from_reference (arg), + complain); +} + /* Convert the indicated template ARG as necessary to match the indicated template PARM. Returns the converted ARG, or error_mark_node if the conversion was unsuccessful. Error and @@ -9060,23 +9087,8 @@ convert_template_argument (tree parm, && same_type_p (TREE_TYPE (orig_arg), t)) orig_arg = TREE_OPERAND (orig_arg, 0); - if (!dependent_implicit_conv_p (t, orig_arg, force_conv)) - /* We used to call digest_init here. However, digest_init - will report errors, which we don't want when complain - is zero. More importantly, digest_init will try too - hard to convert things: for example, `0' should not be - converted to pointer type at this point according to - the standard. Accepting this is not merely an - extension, since deciding whether or not these - conversions can occur is part of determining which - function template to call, or whether a given explicit - argument specification is valid. */ - val = convert_nontype_argument (t, orig_arg, complain); - else - { - val = canonicalize_expr_argument (orig_arg, complain); - val = maybe_convert_nontype_argument (t, val, force_conv); - } + val = convert_nontype_argument_maybe_dependent (t, orig_arg, force_conv, + complain); if (val == NULL_TREE) val = error_mark_node; @@ -26567,10 +26579,12 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict, && !TEMPLATE_PARM_PARAMETER_PACK (parm)) return unify_parameter_pack_mismatch (explain_p, parm, arg); - { - bool removed_attr = false; - arg = strip_typedefs_expr (arg, &removed_attr); - } + arg = convert_nontype_argument_maybe_dependent (tparm, arg, + /*forced=*/false, + complain); + if (!arg || arg == error_mark_node) + return unify_invalid (explain_p); + TREE_VEC_ELT (INNERMOST_TEMPLATE_ARGS (targs), idx) = arg; return unify_success (explain_p); diff --git a/gcc/testsuite/g++.dg/template/deduce11.C b/gcc/testsuite/g++.dg/template/deduce11.C new file mode 100644 index 000000000000..c7671c043974 --- /dev/null +++ b/gcc/testsuite/g++.dg/template/deduce11.C @@ -0,0 +1,15 @@ +// PR c++/107124 +// { dg-do compile { target c++11 } } + +template<int> +struct A {}; + +template<const int &I> +constexpr int f (A<I>) { return 0; } + +template<typename T> +constexpr int f (T) { return 1; } + +const int a = 42; +static_assert (f (A<0>{}) == 1, ""); +static_assert (f (A<a>{}) == 1, ""); diff --git a/gcc/testsuite/g++.dg/template/deduce12.C b/gcc/testsuite/g++.dg/template/deduce12.C new file mode 100644 index 000000000000..0bd2762edd42 --- /dev/null +++ b/gcc/testsuite/g++.dg/template/deduce12.C @@ -0,0 +1,12 @@ +// PR c++/107124 +// { dg-do compile { target c++11 } } + +template<int> +struct A {}; + +template<const int &I> +constexpr int f (A<I>) { return 0; } + +constexpr int i = f (A<0>{}); // { dg-error "no matching function for call" } +// { dg-message "(candidate|does not bind directly|could not convert)" "candidate note" { target c++17 } .-1 } +// { dg-message "(candidate|not a valid template argument)" "candidate note" { target c++14_down } .-2 }
