[C++ PATCH v2] PR c++/93324 - ICE with -Wall on constexpr if.

[Marek Polacek]

On Sun, Jan 19, 2020 at 10:00:42PM +0100, Jakub Jelinek wrote:
> On Sun, Jan 19, 2020 at 03:34:48PM -0500, Marek Polacek wrote:
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > 
> > 	* semantics.c (is_std_constant_evaluated_p): Check fndecl.
> > 
> > 	* g++.dg/cpp1z/constexpr-if33.C: New test.
> > ---
> >  gcc/cp/semantics.c                          |  4 ++--
> >  gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C | 16 ++++++++++++++++
> >  2 files changed, 18 insertions(+), 2 deletions(-)
> >  create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C
> > 
> > diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
> > index 3669b247e34..9051a2863e0 100644
> > --- a/gcc/cp/semantics.c
> > +++ b/gcc/cp/semantics.c
> > @@ -734,8 +734,8 @@ is_std_constant_evaluated_p (tree fn)
> >      return false;
> >  
> >    tree fndecl = cp_get_callee_fndecl_nofold (fn);
> > -  if (fndecl_built_in_p (fndecl, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
> > -			 BUILT_IN_FRONTEND))
> > +  if (fndecl && fndecl_built_in_p (fndecl, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
> > +				   BUILT_IN_FRONTEND))
> >      return true;
> >  
> >    if (!decl_in_std_namespace_p (fndecl))
> 
> Shouldn't it instead do
>   if (fndecl == NULL_TREE)
>     return false;
> before the fndecl_built_in_p check?
> 
> While decl_in_std_namespace_p apparently will return false for NULL
> argument, relying on that is werid.

Can do that, too.

-- >8 --
This is a crash with constexpr if, when trying to see if the call in
the if-statement is std::is_constant_evaluated.

cp_get_callee_fndecl_nofold can return NULL_TREE and fndecl_built_in_p
doesn't expect to get a null tree, so check FNDECL first.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

	* semantics.c (is_std_constant_evaluated_p): Check fndecl.

	* g++.dg/cpp1z/constexpr-if33.C: New test.
---
 gcc/cp/semantics.c                          |  3 +++
 gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C | 16 ++++++++++++++++
 2 files changed, 19 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 3669b247e34..3b88f1520bc 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -734,6 +734,9 @@ is_std_constant_evaluated_p (tree fn)
     return false;
 
   tree fndecl = cp_get_callee_fndecl_nofold (fn);
+  if (fndecl == NULL_TREE)
+    return false;
+
   if (fndecl_built_in_p (fndecl, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
 			 BUILT_IN_FRONTEND))
     return true;
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C
new file mode 100644
index 00000000000..e5ef659932b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if33.C
@@ -0,0 +1,16 @@
+// PR c++/93324 - ICE with -Wall on constexpr if.
+// { dg-do compile { target c++17 } }
+// { dg-options "-Wall" }
+
+struct {
+  template <int>
+  static constexpr bool a() { return 0; }
+} e;
+
+template <typename>
+void d()
+{
+  auto c(e);
+  using b = decltype(c);
+  if constexpr (b::a<2>());
+}

base-commit: bcfc2227c556f2801a657ce3007374732baa8333
-- 
2.24.1