Re: [PATCH] c++: fix ICE with -Wduplicated-cond [PR107593]

[Marek Polacek <polacek@redhat.com>]

On Fri, Jan 27, 2023 at 05:15:00PM -0500, Patrick Palka wrote:
> On Thu, 26 Jan 2023, Marek Polacek via Gcc-patches wrote:
> 
> > Here we crash because a CAST_EXPR, representing T(), doesn't have
> > its operand, and operand_equal_p's STRIP_ANY_LOCATION_WRAPPER doesn't
> > expect that.  (o_e_p is called from warn_duplicated_cond_add_or_warn.)
> > 
> > In the past we've adjusted o_e_p to better cope with template codes,
> > but in this case I think we just want to avoid attempting to warn
> > about inst-dependent expressions; I don't think I've ever envisioned
> > -Wduplicated-cond to warn about them.
> > 
> > The ICE started with r12-6022, two-stage name lookup for overloaded
> > operators, which gave dependent operators a TREE_TYPE (in particular,
> > DEPENDENT_OPERATOR_TYPE), so we no longer bail out here in o_e_p:
> > 
> >   /* Similar, if either does not have a type (like a template id),
> >      they aren't equal.  */
> >   if (!TREE_TYPE (arg0) || !TREE_TYPE (arg1))
> >     return false;
> > 
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > 
> > 	PR c++/107593
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* parser.cc (cp_parser_selection_statement): Don't do
> > 	-Wduplicated-cond when the condition is dependent.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* g++.dg/warn/Wduplicated-cond3.C: New test.
> > ---
> >  gcc/cp/parser.cc                              |  3 +-
> >  gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C | 38 +++++++++++++++++++
> >  2 files changed, 40 insertions(+), 1 deletion(-)
> >  create mode 100644 gcc/testsuite/g++.dg/warn/Wduplicated-cond3.C
> > 
> > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> > index 4cdc1cd472f..3df85d49e16 100644
> > --- a/gcc/cp/parser.cc
> > +++ b/gcc/cp/parser.cc
> > @@ -13209,7 +13209,8 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p,
> >  	    /* Add the condition.  */
> >  	    condition = finish_if_stmt_cond (condition, statement);
> >  
> > -	    if (warn_duplicated_cond)
> > +	    if (warn_duplicated_cond
> > +		&& !instantiation_dependent_expression_p (condition))
> >  	      warn_duplicated_cond_add_or_warn (token->location, condition,
> >  						&chain);
> 
> I noticed warn_duplicated_cond_add_or_warn already has logic to handle
> TREE_SIDE_EFFECTS conditions by invaliding the entire chain.  I wonder
> if we'd want to do the same for instantiation-dep conditions?

warn_duplicated_cond_add_or_warn lives in c-family/c-warn.cc so I can't
use instantiation_dependent_expression_p there.  Sure, I could write a
C++ wrapper but with my patch we just won't add CONDITION to the chain
which I thought would work just as well.

Marek