On Mon, Jan 17, 2022 at 01:48:48PM -0500, Jason Merrill wrote: > 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?
In other words, I think you're asking: why did fixup_deferred_exception_variants set TYPE_CANONICAL (#2) to #1 (which then differs from TYPE_CANONICAL (#3), which is #2)? The method_type for #1 (I'll mark is as #1 here) is built with it being its own canonical type. The first call to fixup_deferred_exception_variants does not change it: in there, VARIANT is #1, the loop with 'TYPE_CANONICAL (v) == v' cannot find an existing variant that would match, so when we do v = build_cp_fntype_variant (TYPE_CANONICAL (variant), rqual, cr, false); we get #1 so TYPE_CANONICAL (variant) = v; is just TYPE_CANONICAL (#1) = #1; so no change. The second call to fixup_deferred_exception_variants: here we're working with VARIANT #2. Now we again scan the list of variants {main, #2, #1} where we find a match for #2: #1. #1's TYPE_CANONICAL is #1 as per above, so we set TYPE_CANONICAL (#2) = #1; which I think is correct. I think TYPE_CANONICAL (#3) should also be #1, not #2, which my patch attempts to do. Hope this explanation makes some sense, please ask away if it doesn't! > > 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 variants > > first. */ > > + 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 > Marek