[PATCH] c++: ICE when mangling operator name [PR98545]

[Marek Polacek]

On Tue, Jan 19, 2021 at 03:47:47PM -0500, Jason Merrill via Gcc-patches wrote:
> On 1/13/21 6:39 PM, Marek Polacek wrote:
> > r11-6301 added some asserts in mangle.c, and now we trip over one of
> > them.  In particular, it's the one asserting that we didn't get
> > IDENTIFIER_ANY_OP_P when mangling an expression with a dependent name.
> > 
> > As this testcase shows, it's possible to get that, so turn the assert
> > into an if and write "on".  That changes the mangling in the following
> > way:
> > 
> > With this patch:
> > 
> > $ c++filt _ZN1i1hIJ1adS1_EEEDTcldtdefpTonclspcvT__EEEDpS2_
> > decltype (((*this).(operator()))((a)(), (double)(), (a)())) i::h<a, double, a>(a, double, a)
> > 
> > G++10:
> > $ c++filt _ZN1i1hIJ1adS1_EEEDTcldtdefpTclspcvT__EEEDpS2_
> > decltype (((*this).(operator()))((a)(), (double)(), (a)())) i::h<a, double, a>(a, double, a)
> > 
> > clang++/icc:
> > $ c++filt _ZN1i1hIJ1adS1_EEEDTclonclspcvT__EEEDpS2_
> > decltype ((operator())((a)(), (double)(), (a)())) i::h<a, double, a>(a, double, a)
> > 
> > I'm not sure why we differ in the "(*this)." part
> 
> Is there a PR for that?

I just opened 98756, because I didn't find any.  I can investigate where that
(*this) comes from, though it's not readily clear to me if this is a bug or not.

> > but at least the
> > suffix "onclspcvT__EEEDpS2_" is the same for all three compilers.  So
> > I hope the following fix makes sense.
> > 
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	PR c++/98545
> > 	* mangle.c (write_expression): When the expression is a dependent name
> > 	and an operator name, write "on" before writing its name.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	PR c++/98545
> > 	* g++.dg/abi/mangle76.C: New test.
> > ---
> >   gcc/cp/mangle.c                     |  3 ++-
> >   gcc/testsuite/g++.dg/abi/mangle76.C | 39 +++++++++++++++++++++++++++++
> >   2 files changed, 41 insertions(+), 1 deletion(-)
> >   create mode 100644 gcc/testsuite/g++.dg/abi/mangle76.C
> > 
> > diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
> > index 11eb8962d28..bb3c4b76d33 100644
> > --- a/gcc/cp/mangle.c
> > +++ b/gcc/cp/mangle.c
> > @@ -3349,7 +3349,8 @@ write_expression (tree expr)
> >     else if (dependent_name (expr))
> >       {
> >         tree name = dependent_name (expr);
> > -      gcc_assert (!IDENTIFIER_ANY_OP_P (name));
> > +      if (IDENTIFIER_ANY_OP_P (name))
> > +	write_string ("on");
> 
> Any mangling change needs to handle different -fabi-versions; see the
> similar code in write_member_name.

Ah, I only looked at the unguarded IDENTIFIER_ANY_OP_P checks.  But now
I have a possibly stupid question: what version should I check?  We have
Version 11 for which the manual already says "corrects the mangling of
sizeof... expressions and *operator names*", so perhaps I could tag along
and check abi_version_at_least (11).  Or should I check Version 15 and
update the manual?
 
> And why doesn't this go through write_member_name?

We go through write_member_name:

#0  fancy_abort (file=0x2b98ef8 "/home/mpolacek/src/gcc/gcc/cp/mangle.c", line=3352, 
    function=0x2b99751 "write_expression") at /home/mpolacek/src/gcc/gcc/diagnostic.c:1884
#1  0x0000000000bee91b in write_expression (expr=<overload 0x7fffea02eb20>)
    at /home/mpolacek/src/gcc/gcc/cp/mangle.c:3352
#2  0x0000000000beb3e2 in write_member_name (member=<baselink 0x7fffea043ae0>)
    at /home/mpolacek/src/gcc/gcc/cp/mangle.c:2892
#3  0x0000000000beee70 in write_expression (expr=<component_ref 0x7fffea043b40>)
    at /home/mpolacek/src/gcc/gcc/cp/mangle.c:3405
#4  0x0000000000bef1be in write_expression (expr=<call_expr 0x7fffe9ede118>)
    at /home/mpolacek/src/gcc/gcc/cp/mangle.c:3455
#5  0x0000000000be858a in write_type (type=<decltype_type 0x7fffea04b348>)
    at /home/mpolacek/src/gcc/gcc/cp/mangle.c:2343

so in write_member_name MEMBER is a BASELINK so we don't enter the
identifier_p block.

Marek