| Message ID | 20231218195021.1244349-1-ppalka@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | c++: bad direct reference binding [PR113064] | expand |
On 12/18/23 14:50, Patrick Palka wrote: > Bootstrappde and regtested on x86_64-pc-linux-gnu, does this look OK for > trunk? OK. > -- >8 -- > > When computing a direct conversion to reference type fails and yields a > bad conversion, reference_binding incorrectly commits to that conversion > rather than attempting a conversion via a temporary. This leads to us > rejecting the first testcase because the direct bad conversion to B&& via > the && conversion operator prevents us from considering the (good) > conversion via a temporary and the & conversion operator (and similarly > for the second more elaborate testcase). This patch fixes this by > making reference_binding not prematurely commit to such a bad direct > conversion. We still fall back to such a bad direct conversion if using > a temporary also fails (otherwise the diagnostic for cpp0x/explicit7.C > regresses). > > PR c++/113064 > > gcc/cp/ChangeLog: > > * call.cc (reference_binding): Still try a conversion via a > temporary if a direct conversion was bad. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp0x/rv-conv4.C: New test. > * g++.dg/cpp0x/rv-conv5.C: New test. > --- > gcc/cp/call.cc | 22 ++++++++++++++++++---- > gcc/testsuite/g++.dg/cpp0x/rv-conv4.C | 16 ++++++++++++++++ > gcc/testsuite/g++.dg/cpp0x/rv-conv5.C | 23 +++++++++++++++++++++++ > 3 files changed, 57 insertions(+), 4 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp0x/rv-conv4.C > create mode 100644 gcc/testsuite/g++.dg/cpp0x/rv-conv5.C > > diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc > index 6ac87a298b2..b5d90359160 100644 > --- a/gcc/cp/call.cc > +++ b/gcc/cp/call.cc > @@ -1739,6 +1739,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, > tsubst_flags_t complain) > { > conversion *conv = NULL; > + conversion *bad_direct_conv = nullptr; > tree to = TREE_TYPE (rto); > tree from = rfrom; > tree tfrom; > @@ -1925,13 +1926,23 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, > z_candidate *cand = build_user_type_conversion_1 (rto, expr, flags, > complain); > if (cand) > - return cand->second_conv; > + { > + if (!cand->second_conv->bad_p) > + return cand->second_conv; > + > + /* Direct reference binding wasn't successful and yielded > + a bad conversion. Proceed with trying to use a temporary > + instead, and if that also fails then we'll return this bad > + conversion rather than no conversion for sake of better > + diagnostics. */ > + bad_direct_conv = cand->second_conv; > + } > } > > /* From this point on, we conceptually need temporaries, even if we > elide them. Only the cases above are "direct bindings". */ > if (flags & LOOKUP_NO_TEMP_BIND) > - return NULL; > + return bad_direct_conv ? bad_direct_conv : nullptr; > > /* [over.ics.rank] > > @@ -1972,6 +1983,9 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, > there's no strictly viable candidate. */ > if (!maybe_valid_p && (flags & LOOKUP_SHORTCUT_BAD_CONVS)) > { > + if (bad_direct_conv) > + return bad_direct_conv; > + > conv = alloc_conversion (ck_deferred_bad); > conv->bad_p = true; > return conv; > @@ -1995,7 +2009,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, > conv = implicit_conversion (to, from, expr, c_cast_p, > flags, complain); > if (!conv) > - return NULL; > + return bad_direct_conv ? bad_direct_conv : nullptr; > > if (conv->user_conv_p) > { > @@ -2018,7 +2032,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, > = reference_binding (rto, ftype, NULL_TREE, c_cast_p, > sflags, complain); > if (!new_second) > - return NULL; > + return bad_direct_conv ? bad_direct_conv : nullptr; > conv = merge_conversion_sequences (t, new_second); > gcc_assert (maybe_valid_p || conv->bad_p); > return conv; > diff --git a/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C b/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C > new file mode 100644 > index 00000000000..fea2e57531a > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C > @@ -0,0 +1,16 @@ > +// PR c++/113064 > +// { dg-do compile { target c++11 } } > + > +struct B { }; > + > +struct A { > + operator B() &; // #1 > + operator B&&() &&; // #2 > +}; > + > +void g(B&&); > + > +int main() { > + A a; > + g(a); > +} > diff --git a/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C b/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C > new file mode 100644 > index 00000000000..dcb6fc6f76f > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C > @@ -0,0 +1,23 @@ > +// PR c++/113064 > +// { dg-do compile { target c++11 } } > + > +struct no_copy { > + no_copy() = default; > + > + no_copy(const no_copy&) = delete; > + no_copy(no_copy&&); > + > + no_copy& operator=(const no_copy&) = delete; > + no_copy& operator=(no_copy&&); > +}; > + > +struct A { > + operator no_copy() &; > + operator no_copy&&() && = delete; > +}; > + > +int main() { > + no_copy nc; > + A a; > + nc = a; > +}
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc index 6ac87a298b2..b5d90359160 100644 --- a/gcc/cp/call.cc +++ b/gcc/cp/call.cc @@ -1739,6 +1739,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, tsubst_flags_t complain) { conversion *conv = NULL; + conversion *bad_direct_conv = nullptr; tree to = TREE_TYPE (rto); tree from = rfrom; tree tfrom; @@ -1925,13 +1926,23 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, z_candidate *cand = build_user_type_conversion_1 (rto, expr, flags, complain); if (cand) - return cand->second_conv; + { + if (!cand->second_conv->bad_p) + return cand->second_conv; + + /* Direct reference binding wasn't successful and yielded + a bad conversion. Proceed with trying to use a temporary + instead, and if that also fails then we'll return this bad + conversion rather than no conversion for sake of better + diagnostics. */ + bad_direct_conv = cand->second_conv; + } } /* From this point on, we conceptually need temporaries, even if we elide them. Only the cases above are "direct bindings". */ if (flags & LOOKUP_NO_TEMP_BIND) - return NULL; + return bad_direct_conv ? bad_direct_conv : nullptr; /* [over.ics.rank] @@ -1972,6 +1983,9 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, there's no strictly viable candidate. */ if (!maybe_valid_p && (flags & LOOKUP_SHORTCUT_BAD_CONVS)) { + if (bad_direct_conv) + return bad_direct_conv; + conv = alloc_conversion (ck_deferred_bad); conv->bad_p = true; return conv; @@ -1995,7 +2009,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, conv = implicit_conversion (to, from, expr, c_cast_p, flags, complain); if (!conv) - return NULL; + return bad_direct_conv ? bad_direct_conv : nullptr; if (conv->user_conv_p) { @@ -2018,7 +2032,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags, = reference_binding (rto, ftype, NULL_TREE, c_cast_p, sflags, complain); if (!new_second) - return NULL; + return bad_direct_conv ? bad_direct_conv : nullptr; conv = merge_conversion_sequences (t, new_second); gcc_assert (maybe_valid_p || conv->bad_p); return conv; diff --git a/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C b/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C new file mode 100644 index 00000000000..fea2e57531a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C @@ -0,0 +1,16 @@ +// PR c++/113064 +// { dg-do compile { target c++11 } } + +struct B { }; + +struct A { + operator B() &; // #1 + operator B&&() &&; // #2 +}; + +void g(B&&); + +int main() { + A a; + g(a); +} diff --git a/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C b/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C new file mode 100644 index 00000000000..dcb6fc6f76f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C @@ -0,0 +1,23 @@ +// PR c++/113064 +// { dg-do compile { target c++11 } } + +struct no_copy { + no_copy() = default; + + no_copy(const no_copy&) = delete; + no_copy(no_copy&&); + + no_copy& operator=(const no_copy&) = delete; + no_copy& operator=(no_copy&&); +}; + +struct A { + operator no_copy() &; + operator no_copy&&() && = delete; +}; + +int main() { + no_copy nc; + A a; + nc = a; +}