On 1/14/22 19:22, Marek Polacek wrote:
This is a "canonical types differ for identical types" ICE, which started with r11-4682. It's a bit tricky to explain. Consider:template <typename T> struct S { S<T> bar() noexcept(T::value); // #1 S<T> foo() noexcept(T::value); // #2 }; template <typename T> S<T> S<T>::foo() noexcept(T::value) {} // #3 We ICE because #3 and #2 have the same type, but their canonical types differ: TYPE_CANONICAL (#3) == #2 but TYPE_CANONICAL (#2) == #1. The member functions #1 and #2 have the same type. However, since their noexcept-specifier is deferred, when parsing them, we create a variant for both of them, because DEFERRED_PARSE cannot be compared. In other words, build_cp_fntype_variant's tree v = TYPE_MAIN_VARIANT (type); for (; v; v = TYPE_NEXT_VARIANT (v)) if (cp_check_qualified_type (v, type, type_quals, rqual, raises, late)) return v; will *not* find an existing variant when creating a method_type for #2, so we have to create a new one. But then we perform delayed parsing and call fixup_deferred_exception_variants for #1 and #2. f_d_e_v will replace TYPE_RAISES_EXCEPTIONS with the newly parsed noexcept-specifier. It also sets TYPE_CANONICAL (#2) to #1. Both noexcepts turned out to be the same, so now we have two equivalent variants in the list! I.e., +-----------------+ +-----------------+ +-----------------+ | main | | #2 | | #1 | | S S::<T379>(S*) |----->| S S::<T37c>(S*) |----->| S S::<T37a>(S*) |----->NULL | - | | noex(T::value) | | noex(T::value) | +-----------------+ +-----------------+ +-----------------+ Then we get to #3. As for #1 and #2, grokdeclarator calls build_memfn_type, which ends up calling build_cp_fntype_variant, which will use the loop above to look for an existing variant. The first one that matches cp_check_qualified_type will be used, so we use #2 rather than #1, and the TYPE_CANONICAL mismatch follows. Hopefully that makes sense.
Why doesn't the TYPE_CANONICAL (v) == v check prevent this?
As for the fix, I didn't think I could rewrite the method_type #2 with #1 because the type may have escaped via decltype. So my approach is to elide #2 from the list, so when looking for a matching variant, we always find #1 (#2 remains live though, which admittedly sounds sort of dodgy). Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/11? PR c++/101715 gcc/cp/ChangeLog: * tree.c (fixup_deferred_exception_variants): Remove duplicate variants after parsing the exception specifications. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/noexcept72.C: New test. * g++.dg/cpp0x/noexcept73.C: New test. --- gcc/cp/tree.c | 16 +++++++++++++++- gcc/testsuite/g++.dg/cpp0x/noexcept72.C | 21 +++++++++++++++++++++ gcc/testsuite/g++.dg/cpp0x/noexcept73.C | 13 +++++++++++++ 3 files changed, 49 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/noexcept72.C create mode 100644 gcc/testsuite/g++.dg/cpp0x/noexcept73.C diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c index 7f7de86b4e8..2efad49e7c1 100644 --- a/gcc/cp/tree.c +++ b/gcc/cp/tree.c @@ -2804,8 +2804,9 @@ fixup_deferred_exception_variants (tree type, tree raises)/* Though sucky, this walk will process the canonical variantsfirst. */ + tree prev = NULL_TREE; for (tree variant = TYPE_MAIN_VARIANT (type); - variant; variant = TYPE_NEXT_VARIANT (variant)) + variant; prev = variant, variant = TYPE_NEXT_VARIANT (variant)) if (TYPE_RAISES_EXCEPTIONS (variant) == original) { gcc_checking_assert (variant != TYPE_MAIN_VARIANT (type)); @@ -2827,6 +2828,19 @@ fixup_deferred_exception_variants (tree type, tree raises) v = build_cp_fntype_variant (TYPE_CANONICAL (variant), rqual, cr, false); TYPE_CANONICAL (variant) = v; + + /* If VARIANT became a duplicate (cp_check_qualified_type-wise) + of an existing variant in the variant list of TYPE after we + have parsed its exception specification, elide it. Otherwise, + build_cp_fntype_variant would use it, leading to "canonical + types differ for identical types." */ + for (v = TYPE_MAIN_VARIANT (type); v; v = TYPE_NEXT_VARIANT (v)) + if (v != variant + /* The main variant will not have TYPE_RAISES_EXCEPTIONS + so PREV should never be null. */ + && cp_check_qualified_type (v, variant, var_quals, + rqual, cr, false)) + TYPE_NEXT_VARIANT (prev) = TYPE_NEXT_VARIANT (variant); } else TYPE_RAISES_EXCEPTIONS (variant) = raises; diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept72.C b/gcc/testsuite/g++.dg/cpp0x/noexcept72.C new file mode 100644 index 00000000000..f1455b3b46b --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept72.C @@ -0,0 +1,21 @@ +// PR c++/101715 +// { dg-do compile { target c++11 } } + +template <typename T> struct S { + S<T> bar() noexcept(T::value); // #1 + S<T> foo() noexcept(T::value); // #2 +}; + +template <typename T> S<T> S<T>::foo() noexcept(T::value) {} // #3 + +template <typename T> struct S2 { + S2<T> bar1() noexcept(T::value); + S2<T> bar2() noexcept(T::value); + S2<T> bar3() noexcept(T::value); + S2<T> bar4() noexcept(T::value); + S2<T> bar5() noexcept(T::value); + S2<T> baz() noexcept(T::value2); + S2<T> foo() noexcept(T::value); +}; + +template <typename T> S2<T> S2<T>::foo() noexcept(T::value) {} diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept73.C b/gcc/testsuite/g++.dg/cpp0x/noexcept73.C new file mode 100644 index 00000000000..24524f3592a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept73.C @@ -0,0 +1,13 @@ +// PR c++/101715 +// { dg-do compile { target c++11 } } + +template <typename T> struct S { }; + +template<typename T> +struct A +{ + A& foo(A&&) noexcept((S<T>::value)); + A& assign(A&&) noexcept((S<T>::value)); +}; +template<typename T> +A<T>& A<T>::foo(A&&) noexcept((S<T>::value)) {} base-commit: 952b7dbb418198f86d7829aaf9d7f9fc7714a8b3
