On Thu, Jan 20, 2022 at 03:23:24PM -0500, Jason Merrill wrote:
> On 1/18/22 11:05, Marek Polacek wrote:
> > 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)?
>
> I meant to ask why TYPE_CANONICAL (#3) got set to #2 instead of #1?
>
> And to answer my own question, it's because the check I mention is in
> fixup_deferred_exception_variants, and #3 doesn't go through there at all;
> the loop in build_cp_fntype_variant assumes no duplicate variants, which
> your patch fixes.
Right, fixup_deferred_exception_variants is only called for fn decls in
unparsed_noexcepts.
> > 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);
>
> I think we don't two loops through the variants. It ought to work to
> replace the existing loop with yours; if we find v, we prune and use its
> TYPE_CANONICAL.
Ah yes, good idea; I don't actually need to wait till TYPE_RAISES_EXCEPTIONS
is set on variant! The following seems to work just as well.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
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.
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).
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.cc | 16 ++++++++++++++--
gcc/testsuite/g++.dg/cpp0x/noexcept72.C | 21 +++++++++++++++++++++
gcc/testsuite/g++.dg/cpp0x/noexcept73.C | 13 +++++++++++++
3 files changed, 48 insertions(+), 2 deletions(-)
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.cc b/gcc/cp/tree.cc
index bcd44e73921..17436f0512d 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -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));
@@ -2815,12 +2816,23 @@ fixup_deferred_exception_variants (tree type, tree
raises)
cp_cv_quals var_quals = TYPE_QUALS (variant);
cp_ref_qualifier rqual = type_memfn_rqual (variant);
+ /* If VARIANT would become a dup (cp_check_qualified_type-wise)
+ of an existing variant in the variant list of TYPE after its
+ exception specification has been parsed, elide it. Otherwise,
+ build_cp_fntype_variant could use it, leading to "canonical
+ types differ for identical types." */
tree v = TYPE_MAIN_VARIANT (type);
for (; v; v = TYPE_NEXT_VARIANT (v))
if (TYPE_CANONICAL (v) == v
+ && v != variant
&& cp_check_qualified_type (v, variant, var_quals,
rqual, cr, false))
- break;
+ {
+ /* The main variant will not match V, so PREV will never
+ be null. */
+ TYPE_NEXT_VARIANT (prev) = TYPE_NEXT_VARIANT (variant);
+ break;
+ }
TYPE_RAISES_EXCEPTIONS (variant) = raises;
if (!v)
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: d2ad748eeef0dd260f3993b8dcbffbded3240a0a
--
2.34.1
