Re: [PATCH] c++: recalculating local specs via build_extra_args [PR114303]

[Patrick Palka <ppalka@redhat.com>]

On Tue, 26 Mar 2024, Patrick Palka wrote:

> On Mon, 11 Mar 2024, Patrick Palka wrote:
> 
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look
> > OK for trunk and release branches?
> 
> Ping.

Ping.

> 
> > 
> > -- >8 --
> > 
> > r13-6452-g341e6cd8d603a3 made build_extra_args walk evaluated contexts
> > first so that we prefer processing a local specialization in an evaluated
> > context even if its first use is in an unevaluated context.  But this
> > means we need to avoid walking a tree that already has extra args/specs
> > saved because the list of saved specs appears to be an evaluated
> > context.  It seems then that we should be calculating the saved specs
> > from scratch each time, rather than potentially walking the saved specs
> > list from an earlier partial instantiation when calling build_extra_args
> > a second time around.
> > 
> > 	PR c++/114303
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* constraint.cc (tsubst_requires_expr): Clear
> > 	REQUIRES_EXPR_EXTRA_ARGS before calling build_extra_args.
> > 	* pt.cc (tsubst_stmt) <case IF_STMT>: Call build_extra_args
> > 	on the new IF_STMT instead of t which might already have
> > 	IF_STMT_EXTRA_ARGS.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* g++.dg/cpp1z/constexpr-if-lambda6.C: New test.
> > ---
> >  gcc/cp/constraint.cc                             |  1 +
> >  gcc/cp/pt.cc                                     |  2 +-
> >  .../g++.dg/cpp1z/constexpr-if-lambda6.C          | 16 ++++++++++++++++
> >  3 files changed, 18 insertions(+), 1 deletion(-)
> >  create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if-lambda6.C
> > 
> > diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> > index 49de3211d4c..8a3b5d80ba7 100644
> > --- a/gcc/cp/constraint.cc
> > +++ b/gcc/cp/constraint.cc
> > @@ -2362,6 +2362,7 @@ tsubst_requires_expr (tree t, tree args, sat_info info)
> >  	 matching or dguide constraint rewriting), in which case we need
> >  	 to partially substitute.  */
> >        t = copy_node (t);
> > +      REQUIRES_EXPR_EXTRA_ARGS (t) = NULL_TREE;
> >        REQUIRES_EXPR_EXTRA_ARGS (t) = build_extra_args (t, args, info.complain);
> >        return t;
> >      }
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index 8cf0d5b7a8d..37f2392d035 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -18718,7 +18718,7 @@ tsubst_stmt (tree t, tree args, tsubst_flags_t complain, tree in_decl)
> >  	  IF_COND (stmt) = IF_COND (t);
> >  	  THEN_CLAUSE (stmt) = THEN_CLAUSE (t);
> >  	  ELSE_CLAUSE (stmt) = ELSE_CLAUSE (t);
> > -	  IF_STMT_EXTRA_ARGS (stmt) = build_extra_args (t, args, complain);
> > +	  IF_STMT_EXTRA_ARGS (stmt) = build_extra_args (stmt, args, complain);
> >  	  add_stmt (stmt);
> >  	  break;
> >  	}
> > diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if-lambda6.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if-lambda6.C
> > new file mode 100644
> > index 00000000000..038c2a41210
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if-lambda6.C
> > @@ -0,0 +1,16 @@
> > +// PR c++/114303
> > +// { dg-do compile { target c++17 } }
> > +
> > +struct A { static constexpr bool value = true; };
> > +
> > +int main() {
> > +  [](auto x1) {
> > +    return [&](auto) {
> > +      return [&](auto x3) {
> > +        if constexpr (decltype(x3)::value) {
> > +          static_assert(decltype(x1)::value);
> > +        }
> > +      }(A{});
> > +    }(0);
> > +  }(A{});
> > +}
> > -- 
> > 2.44.0.165.ge09f1254c5
> > 
> > 
>